Fun with Robots, IR Decoding, LED Matrix, etc.

Fig 1: Three experiment--two with the samsung remote on the left, one with the Radio Shack remote on the right--to control a +Adafruit Industries 8x8 Bicolor LED Matrix

I haven't posted in a while because several interests have kept me very busy. This all started withe the +Parallax Board of Education (BOE) Robot kit. I asked for and received on for Christmas a couple of years ago and let it ripen until I was ready.  I decided that it would make a good project to do with my 7-year-old granddaughter when she visits this summer--but first, I should make sure that I can build it without a lot of fumbling. Fumbling is good, but watching me figure out what dumb thing I did is not always interesting to a 7yr-old. I followed the tutorial and learned quite a bit, The last project that I did used infrared for proximity sensing to avoid obstacles. At the same time, +Adafruit Industries, via The Desk of Lady Ada, provided some great information on IR. So, I decided to play and learn further.

Fig 2: +Parallax BOE Bot with 2 IR transmitters aand 2 IR receivers

IR Decoding the Hard Way

Following the +Adafruit Industries tutorial on IR Sensing, I was able to decode only some of the buttons on my Samsung TV Remote (see Figure 1). Using the remote is a 2-step process: first decode the signals send by the buttons, then use the decoded signals in a different sketch that takes action based on the buttons. Using this method (see the Raw IR Decoder and ircommander code on github), I was able to decode some of the buttons and use them in a sketch.  

Quick diversion:  I have had big plans to use a 32x32 LED Matrix that I bought in a parking assistant project that will display faces to convey the emotions evoked by a car getting increasingly closer. I decided to use the 8x8 bicolor matrix and backpack to prove the concept, and use the remote to signal which face to display. Figure 1 shows the initialized yellow face (looks orange to me). So, I needed to follow the tutoral for the matrix and backback library.

I was able to merge code from the bicolor8x8 example code in the Adafruit LED Backpack library with code from the ircommander sketch referenced above. After adding the decoded remote buttons to a newly created library (see the IR Sensor tutorial and the project video cited at the end of this post), I was able to change the face on the matrix based on the remote buttons.

I found both the coding aspect and the operation of the technique to be less than perfect.  Maintaining a separate library with very long sequences of numbers just to test what button  was pressed seems a bit much. In operation, the code seems to reset itself randomly, and only respond to buttons when it feels like. This may be me, and I will investigate, but read on to see a much neater technique.

IR Decoding an Easier Way

After working through the above, I watched Lady Ada work through Chris Young's IRLib2 in one of the Desk of Lady Ada epdisodes cited above.  Chris, aka cyborg5, is a frequent visitor to the Adafruit Show and Tell, and has done a lot of great work (see his blog).  Both the decoding and the processing techniques are simplifies greatly, and his library handles several IR protocols. The IRLIB2 tutorial describes it all very well.  You wind up with one simple code that you supply in a sketch so you can determine what button was pressed--straightforward, and I was able to decode all the buttons with no missed presses. From there it was a matter of simplifying the sketch I wrote earlier to display faces on the LED matrix.  Again, the project video shows all this.

Controlling Motors with IR

Since we started with robots, I thought it would be interesting to control motors with IR.  It was a simple matter to modify the IRLib2 sketch above to direct the continuous rotation servos.  I took code from the BOE-Bot project, and code from the Adafruit_PWMServoDriver library tutorial, and it went smoothly.  The servos in the BOE-Bot are different from the Adafruit ones, so I had to go to the data sheet to see what values to use to get them to move as I wanted. I was able to decode all the buttons on the Samsung remote, and used the arrow keys to simulate moving the robot forward, back, left, and right.

I first did this without the PWM Servo FeatherWing. Because the feather is 3V logic, I needed a level shifter to handle the signals from the board to the servos. That worked, but added a few connections and I used the Arduino servo library as opposed to the Adafruit library which allowed for simpler code.

Another thing I needed to worry about was timer conflicts. I had come across this before, in my Donkey Project, but Chris' tutorial gave a straightforward explanation and solution. The problem is that the servo library uses Timer1 and on the 32u4 Feather IRLib2 does too. It was necessary to go into one of the associated libraries and change one line of code to re-assign the timer.  You'll get better instruction in the tutorial than I can give here.  Again, the project video shows the results.

Controlling 2 FS90R continuous rotation servos from an Adafruit BLE Feather and PWM Servo FeatherWing

Trying a Different Remote

A while back, Radio Shack sold some MAKE project kits, including robotics. During an earlier RS bankruptcy, I acquired a RS remote at a big discount and still had it in inventory, so I decided to try it out. Using the IRLib2 approach to decoding, I found the the protocol was not one of supported ones. A look at the datasheet for the PT2248 chip in the remote revealed that ot used the Toshiba protocol. So, I had to go back to the hard way, and I got that to work.  See the video.

IR Affects the BOE-Bot

Just for grins, I took out the BOE-Bot, let it runon the floor, and chased it with a remote.  The bot's IR retrievers detected the transmissions, and the bot reacted accordingly (moving left or right as if it had detected an obstacle).

Project Video

See the project video on YouTube

@Make: Electronics Experiment 34 - Hardware Meets Software

I've been away from this book (Make: Electronics by +charles platt ) for a couple of months.  I have really enjoyed the experiments, and I had planned to finish the book by Christmas 2015 so I could start on the sequel (Make: More Electronics).  US Holidays, grandchildren, and my new interest in amateur radio have gotten in the way.

I opened the book again this week, and started to plan for Experiment 34.  I had been looking forward to it, because it offers the opportunity to mess with a different microcontroller, the PICAXE.  As you can see from other projects on this blog, I have been using +Arduino  for a lot of projects and I really like it. So, I have some experience with microcontrollers, and the software side is no problem--I've been programming for over 40 years in a variety of languages in a variety of environments.

When I got into this experiment, I ran into one of my irritations with the book: the parts lists do not always list all the parts.  In this case, it turns out that PICAXE needs a specific USB cable to upload code.  Not a problem, except that it costs US$20.  If I had seen that when I ordered the parts for this chapter,  would have ordered one.  Now, I'm at the point where I'm not sure if I would ever use PICAXE for any other projects. I have a bunch of Arduinos amd Arduino-like boards, mostly from  +Adafruit Industries, and I'm very happy with the IDE and available tutorials.  I think I would rather spend the money on the next book.

There IS one possibility here: I am looking at ways to make a PICAXE cable.  That might be a worthwhile learning endeavor. I'll look into that more deeply. If I do make a cable and get it to work, I'll do Experiments 34 and 35.  If not, I'll declare myself finished  with the book.  I had already decided to skip Experiment 36 ("The Lock, Revisted") because I don't really have a use for the lock and I think I understand everything Charles is teaching for it.

Give me a couple of weeks.  I'll post my decision then.

@Make: Electronics Experiment 33 - Moving in Steps

This chapter ends with the concept for another robot, this time one that responds to light with photoresistors. I decided not to go all the way with that, because I just spent a whole lot of time on the last cart (much of it on fabrication), and because I plan to follow Charles' upgrade of Experiment 32 as published in Make Magazine (March 2015).

Actually, I had a little trouble with this. First, Charles said to use 12V motors, and I could only find 5V.  I found a set of that came with UL2003A driver boards on Amazon. I did not get the results I expected on the breadboard just using LEDs...I expected to see the cycle of pulses repeat, but it only did one cycle at a time.  I checked the connections many times, with no success.  This particular breadboard has been flaky in the past, but I'm, not willing to rewire the whole thing.

I drove the stepper using an Arduino Uno and some code I found in a tutorial on Instructables.

I made a video.

On to the Picaxe in Experiment 34!

@MAKE #Electronics Experiment 32: Robot Cart (Part III - Cart is together)

The saga continues...

I put the pieces of the cart together as shown here:

I attached the hinge to the body only to expand the pilot holes to make it easier when I put the movable wheel assembly together (see upper right).  The wheel at the lower right has the mounting wheel for the motor ready to go.

Next step was the wheel assembly.  I needed 1" #6 bolts to put the 3 pieces together (each piece is 1/4").  Once I got it together I realized that it was upside down (the holes for the axle needed to be on the bottom), so took it all apart and reassembled.

Next was the driving wheel. The pre-drilled holes in the mounting wheel were not big enough for any screws I had or could get quickly, so I reamed them and used #4 sheet metal screws (needed 1/2"--another shopping trip).  Pan head screws won't do because the wheel needs to clear the motor. Even with flat-head screws I had to file down a small plastic cylinder on the motor, which has no use that I can discern.

Now I was ready to mount the motor. I was clueless here, but I thought ahead enough to buy a mounting bracket, which attaches to the motor with a #4 machine screw (again, 1/2" flat-head). I measured the cylindrical piece to the motor--it's 3/4". I drilled a 3/4" hole in the ABS side (3/4" from the bottom like the other wheels, and over enough so that the wheel did not extend beyond the front of the body--2.25" in). I had to file the hole to get the motor through it, but it's in and stays put. The bracket doesn't do much, but if I need to secure the motor later on, I can screw it to a piece of plywood that I secure to the frame.

The motor is a Solarbotics GM2 Offset Shaft Gear Motor. I used a Solarbotics GMW mounting wheel, and GMB28 Mounting Bracket.

Next was the limit switches.  They need to be in the front with the sensors out so that when they hit something the switch will activate the timer sequence and flop the relay for 5 seconds, reversing the motor. (See my post, including a video, on the circuit.) I drilled the holes (1/8") on both sides but only mounted one, using 3/4" #4 machine screws and nuts.  I'm keeping the other connected to the breadboard circuit for the final pre-completion test.

Next Steps:

• test the circuit again
• construct the circuit on an +Adafruit Industries Perma Proto Board and mount it on standoffs in an Altoids Tin with insulation on the bottom
• test and rework as necessary
• solder everything up and go

Here's what it looks like at this point:

Right view. Note the limit switch on the front.

Front view (driving wheel, motor. limit switch)

Rear view (moveable wheel assembly, hinge)

Left view (motor protruding through hole)

@MAKE #Electronics Experiment 32: Robot Cart (Part IIA-Better)

3rd attempt at the cart.  Used a hand saw this time, and my handy drill. I marked Xs on the pieces I want to cut out to remind me what I'm doing.

Cart is now fabricted.  You can see some damage from bending the frame, but it will do for now.  I may redo it if I like the final product and want to showcase it.

OK, so I can't follow directions. It's a good thing I bought 10 sheets of ABS, because I have ruined 2 now, and may need another.  I got through my measuring, drilling and cutting, only to see that I pu the cuts on the wrong side.  So, I measured and drilled again...that's the top photo..and took the step to mark the pieces that wanted to cut out.

I made the cuts. used my heat gun to soften the plastic, and bent the sides.  I left the final cuts (removing the short pieces on what would become the top) so I could bend those into a position to cut them.  It was ugly.

I'd like to say that I started on the wrong side on purpose (one side is textured and the other smooth), but it was by mistake. It turned out to be almost OK because I had significant shaping and deburring to do, using my Harbor Freight Dremelish tool.

When I bent the frame back to put the textured side out, there was some damage (see lower photo).  It's usable as-is, so I'm going with it.  If I really like the cart when it's done. I'll redo the frame.

Next:
By some 14" plywood, the hardware (hinge, bolts, nuts, screws), and maybe some 3" disks to use as wheels,  as suggested by James Floyd Kelly.

@MAKE #Electronics Experiment 32: Robot Cart (Part II)

So, carpentry and fabrication are not my strong suits. Evidently I'm not real strong on following directions, either. Anyway, this is pass one, and I'll keep at it.

The good news:  I proved that I can use the 12"x12"x1/8" sheets of ABS (that I bought from Amazon about a year a go thinking they's come in handy) for the main cart body.  They're not thick enough to screw into, so I'll add 1/4" plywood, or maybe see if I can find 1/4" ABS.  I was able to cut the sheet to 9"x8", drill holes for rounding corners, then cut the rest, and use my heat gun to soften it for bending into shape See Fig. 5-92 on p. 275.

Problems:

1. I used the wrong saw. That's why the cuts look ugly.  I knew that, but I bought a reciprocating saw at Harbor Freight and have been dying to use it.  I'm going to a hand saw, maybe a coping saw. 
2. I drilled 3 of the holes in the wrong place. The idea is to have 1/2" diameter holes to round the 4 corners of the cut ABS, but you need to drill the holes in the inside of the cut, not the outside (that's why you see some holes that don't appear to be random--they are just wrong).

Other than that it's great.  I'm ready for pass two, and I learned a lot.

@MAKE #Electronics Experiment 32: Robot Cart

I'm ready to start on this. First step was to gather the materials.  The parts list on page 268 is incomplete, although on p. 276 there's a "you will also need..." See the schematic on p.277 and this blog post by +James Floyd Kelly  (it's on experiment 31, but references shopping for 32). The 50K potentiometer shown in the schematic controls the time the motor runs in reverse before going forward again.

Make: Electronics by Charles Platt, Figure 5-98. p.277 (in the edition I have)

Also, the erratum on p. 277 mentions adding a diode or transistor. I'm going to try a diode (handsonelectronics says diode).

I found that my DPDT relays on hand are not appropriate. Some are latching relays bought for experiment 20, and the other was 12V, so I ordered two 5V DPDT non-latching relays from Amazon.

Charles spends a great deal of time on fabrication and not much on the circuit.  Since I care more about the circuit, and there are some issues with it, I'm going to build that first. I'm going to try to use plastic for fabrication. I have some 12"X12" pieces of ABS, and the shell of a multi-function printer that I tore-down.

Here's the concept:
When switched on, the cart moves forward until one of the microswitches hits something, it cuts power to 555 Trigger Pin 2, causing the the Output Pin 3 to pulse the relay, which then flops, reversing voltage to the motor, which reverses. The timer cycle (determined by 555 Threshold Pin 6 and Discharge Pin 7 as powered by the capacitor/resistor combination along with the Pot). When the cycle ends, the Output Pin 3 goes low and the relay flops back, causing the motor to reverse again (making it go forward).

The time it reverses starts at ~5 seconds (47uf cap*100000Ohm resistor = 47//1000000*100000 = 4.7). The Pot did not make much difference, if any. I thought it did, but it turned out that I had unhooked the 100K resistor. DUH.

I had other DUH moments in this, but I was helped immeasurably but people running into the same problems I did, particularly +James Floyd Kelly .  Thank you James. First, I bought a 5V gearmotor from robotshop .com. I fussed around for way too long trying to figure out how to wire it--then I noticed the two copper tabs on the neck.  Second, I was getting weird buzzing from the relay, and the motor was not reversing. I remember the symptoms from James' blog. My relay had different pinouts from the schematic. There are 8 pins. If you number them 1-8 starting with 1 at upper left and go counter clock-wise, I needed to switch pins 2 and 3 on one side and 7 and 6 on the other.  I could not find a datasheet for this relay, but I had a similar issue once before with another DPDT relay, so I guessed.

Third problem was the diode,  The motor would not reverse, but fortunately I had seen this before (thanks James), so I added the diode across pins 1 and 8 of the relay with the cathode towards pin 8.

I also struggled with wiring the switches.  I tested it with just the switches, power supply, and a meter, and came up with:
555 Trigger Pin 2  to switch1 NO prong, connected to switch 2 NO
Both NC Prongs connected to GND
Both COM prongs (on the side--at least on mine) connected to GND

If neither switch is pressed, current is flowing to the trigger pin through the 10K pull-up resistor making it high and thus the output pin is low. When either switch is pressed, the trigger pin goes low, making the output pin high, and flopping the relay and reversing then motor.  The output pin stays high until the 47uf capacitor dishcarges (4.7sec) to the threshold pin, making it high and setting the output pin back to low, flopping the relay back and the moving the motor in the original direction.

It works.  Here's the video.

@MAKE #Electronics Experiment 31: One Radio, No Solder, No Power with thanks to @sqfield (+Simon Field)

This is one of those things I've wanted to do for over 55 years.  If I'd only had more motivation and more support, I would have.  Water under the bridge, so here's my attempt now.

First of all, contrary to Charles' title, there was solder: I was too aggressive with my stripping to create the tapes in the coil, and cut the wire, so I had to solder the two pieces together and add some heat shrink for insulation.

Parts ready for assembly: coil with taps ever 50in, wrapped around vitamin bottle, spool of solid core 22awg hookup wire for ground--40ft left after the coil, germanium diode (on top of the white spool), 100ft og 16awg stranded wire for antenna, piezoelectric earphone, hose clamp to connect ground wire to water pipe. The earphone I bought (from SciToys) has a plug on the end, so I bought a jack for it from Radio Shack and connect the ground and earphone wires to it.

This is +charles platt 's experiment, but he directs the reader to scitoys.com for parts. This website, run by +Simon Field, has a wealth of fun projects.

Before adding the coil and the antenna, I tried a couple of suggestions from SciToys. First, I touched one end of the diode to a water pipe for ground and the other to the ground contact on the phono jack. I held the audio input (left, because it's a stereo jack and the left is where the contact on the mono earphone is) to use my body as an antenna. Got nothing.  Next, I taped the hookup wire to the water pipe and cut off a length of wire that would allow me sit in a chair on my patio, and connected that to the ground on the jack with an alligator clip.  I connected one end of the diode to audio input and held the other end, again being the antenna. Still nothing.

There is an AM tower within about 3 miles, so I think I should be able to get something. Next, I tried adding the coil and the 16awg antienna.  There is lightning in the area for the next couple of days, so I stayed inside: I ran about 60-70ft of wire up the basement stairs through the living room and around the family room. Then, I went back to my basement workshop and assembled what you see in the photo below.

The black and red wires at the bottom go to the water pipe and upstairs.  The green alligator clip lead goes from ground on the jack to the taps on the coil. The red alligator clip lead goes from the diode to audio input on the jack. The paper clip hanging from the tap (upper left) marks where I heard something.

When the weather clears I'll try the antenna outside, but here's what I got:

• I heard static right away in the earphone
• When I moved from tap to tap, the static went away--silence
• At one pint, on one tap, I heard some Spanish--SUCCESS! I couldn't get it back, but I'm happy

I will post again after I move outside. I have some other components too, like a variable capacitor and a coil+ferrite rod, so I will plan adding those while I'm waiting for the weather to clear.

@MAKE #Electronics Experiment 30: Fuzz

From Make: Electronics, by Charles Platt. Sebastopol, CA: Maker Media, Inc, 2009, p 259.

In Experiment 30, we are creating distortion rather than filtering.  It's really an extension of Experiment 29, using a schematic similar to part 2. The differences are:

1. The 10K and 33K resistors on TEA2025B IN1 pin 10 are replaced by an 820 Ohm resistor. The audio input still comes in at this point.
2. There are no filters. The speaker connections go directly to OUT1 (pin 2) and OUT2 (pin 15) of the amp. 
3. The 680K resistor on 555 and 500Ohm Pot on output pin 3 of the 555 are replaced by a .1uf cap, going to the base pin of a 2N2222 transistor (Q1). The rest of the 555 connections are unchanged. The 100K Pot still adjusts frequency.
4.  The big difference is the addtion of the transistors.  The collector of Q1 is connected to power through a 33K resistor. The emitter of Q1 is connected to a 1K resistor and 1uf capacitor, which are also connected to the emitter of Q2.  Q2's base pin is connected to the 33K resistor, power, and Q1's collector. Q2's emitter is connected to a 100K pot through an 8K2 and 390 Ohm resistor and .22uf cap, with the other side of the pot connected to the audio input.

The transistors amplify the waveform coming from the 555, as adjusted by Pot1.  This signal overwhelms the amp, causing distortion to a degree determined by Pot2, which Charles calls the "fuzz adjuster."

I spent some time with the datasheet for the TEA2025B.  It's a stereo amp that we used in "bridge mode" for these Experiments 29 and 30.  The leads to the single speaker are connected to OUT1 and OUT2 (pins 2 and 15), and the audio input goes to IN1 (pin 10). In stereo mode, each speaker would have one lead connected to an output and the other to GND, and the additional audio input would connect to IN2 (Pin 7), which would have the same .22uf cap + resistor combination as IN1,

Another interesting experiment.  I plan to fuss around more with the TEA2025 and associated resistor and capacitor values, just for grins.

One curiosity: as reported here and by +Eric Buijs, the TEA2025 overheats, and overheats a lot at 9V.  I was having trouble getting go0d results from this experiment, so I decided to swap out the chip. It hat melted the breadboard under it, and the new chip gave me what I expected (including overheating).  The datasheet says it will take up to 15V, but at least 2 of us have experienced overheating.

@MAKE #Electronics Experiment 29: Filtering Frequencies Part II

Note: first, apologies to +Eric Buijs who noted that the TEA2025B runs hot at 9V.  I either did not notice or did not perceive that in part 1. However, in part 2 I experienced the same thing. Using an adjustable wall wart, I was able to apply different voltages.  9V works best, but it runs at safer temps at 7,5V and 6V. Besides the heat, the biggest difference is the volume coming out of the speaker (see video at link below).

Part 2 of this experiment involves adding a 555 timer in astable mode (with resistors and capacitors) and two pots: a 500 Ohm for volume control (between output pin 3 of the 555 and the input of the TEA2025B) and a 100K to manipulate the waveform (between 555 discharge pin 7 and threshold pin 6). I skipped the buttons for this exercise, and connected it with each filter and with no filter at all. The differences are discernible.

I did not have a 500Ohm pot, so I used a 1K.  It really only worked as a volume control at 9V.

Charles says to disconnect the audio source and use the timer as input to the amp.  I also added my cell phone playing Pandora back in.  It works for that, too.

A very worthwhile experiment. I'm looking forward to doing more with audio.

Here's the video.

@MAKE #Electronics Experiment 29: Filtering Frequencies Part I

I know very little about audio, etc., so this experiment is very interesting to me.  When I was 10-12 years old, I read about people making hi-fis, ham radios, and the like, and thought I'd like to do that someday.  With neither persistence nor guidance, that interest was never nurtured, but it was always somewhere within me. Thank you Charles for helping to bring it back. 

The photo below shows the breadboard, nearly complete according to the instructions.  The two momentary, normally open push-button switches are for the two filters. The coil is not shown--110ft of 20 gauge hook-up wire, which I had to unwind./rewind to get access to both ends. I used two 22uf electrolytic capacitors, back-to-back, instead of the 10uf NP cap Charles had in the schematic.  I could not find .15uf caps, so I used .22uf. I took the speaker out of an old Sony Trinitron TV before I took it to the dump (also got some pots and other useful stuff). Since I'm totally ignorant, I wasn't following Charles' instructions for connecting audio, so I bought some plugs to fit into the adapter. Once I took the plug apart and saw the connections, I understood what he meant. Since I spent the money (US$4.99 for eight at Radio Shack), I'll use it. Besides, it gives me an excuse to solder. The box for the speaker is a US$1.99 pencil box from K-Mart.  I use them for project boxes, but this seemed like a good application.

Breadboard almost ready, speaker taken from an old TV set, RCA adapter from Radio Shack, and a pencil box from K-Mart

The next photo is the speaker box after I drilled holes. Not the tidiest of jobs, but I think it will work.

Pencil box ready to be a speaker enclosure

Next step, hook up the filters and the music (I'll plug the adapter into my cell phone and play something on Pandora).

The idea is to bring mono input into the amplifier chip. The output goes through either a high-pass (caps) or low-pass filter (coil) to the speaker. I used the RCA adapter to get sound from my cell phone, plugged into one of the jacks in that adapter, and wired the plug to ground and to the 33K resistor/amp input.

Everything hooked up as expected. There is a big difference with and without the coil, not so much with and without the caps. The coil provided more difference after I removed the 33K resistor (also less noise). I will try using smaller caps. In the next post I will add the 555 timer and pots.  I'll add video there too.

This was another simple, but informative experiment.  I love this book. See you in part 2.

@Make #Electronics Experiments 26-28--Fun with Coils

These three experiments, like #25, are pretty short. Since they're related, I decided to do them all together.  I thought of doing this starting with 25, but I did not have all the parts I needed (lacking the spool of magnet wire).  Now that I have what I need, I'm ready.

Here's a video of the three experiments.  Following is a discussion of each part and links to individual (shorter) videos.

Experiment 26: Tabletop Power Generation

This one is neat. It's in two parts:

1. Use a 3/4-inch neodymium magnet to generate alternating current
   By stripping the ends of a 100ft coil of 26-gauge magnet wire on a spool, connecting the ends to an LED, and then moving the magnet up and down through the spool, we generate electricity to light the LED. The LED flashes only on one direction--reverse the connections and it only flashes in the other (alternating current).
   Video.
2. Use a diode to rectify AC current and store in a capacitor
   Using the same coil as in part 1, we use a 1N4001 signal diode and 100uf electrolytic capacitor in series to replace the LED.  We connect a multimeter across the leads of the capacitor to measure volts.  When we move the magnet up and down through the coil, it generates electricity, but the diode blocks one direction, so it's DC.  The capacitor charges up until we stop moving the magnet (I got it to about 2.5V), then it slowly discharges.
   Video.

Experiment 27: Loudspeaker destruction
I fudged this a little because I did not have a 2" speaker. The 1 1/4" Radio Shack cheapie was good enough for demonstration.  The whole point is that there's a coil and a magnet and the inputs to the speaker causes vibrations which are received as sound.
Video.

Experiment 28: Making a Coil React
In this experiment , we power a circuit from 12V DC, passing through a momentary tactile switch, a 220 Ohm resistor, two low-current LEDs oriented in opposite directions, and on through a coil.  When the button is pushed, the coil initially blocks flow so the circuit finds a path through one of the LEDs.  Once the coil;s self-inductance is overcome, it accepts current and the LED goes out.  When we release the button, the current that was stored in the coil releases and lights the other LED.
Video.

@Make #Electronics Experiment 25: Magnetism

Experiment 25 is a very simple grade school experiment on electricity and magnetism.

Charles includes it because it's neat and because he's introducing self-inductance, the third property of passive components (with resistance and capacitance),

I cut 6 feet of 22-gauge hook -up wire and wrapped it ~60 times around a screwdriver. I then attached alligator clips to the ends of the wire. When I connected the other ends of the clips to the poles of a AA battery, the paper clip moves towards the screwdriver. More fun!

Here's the video

Next we go on to generate electricity with a magnet (assuming that I can find 100 feet of magnet wire),

@MAKE Electronics Experiment 24: Gonna Skip It

I've been away, and recovering from being away, for a couple of weeks, so I'm just getting back to my journey of discovery with Charles Platt as my guide.

Experiment 24 involves enhancing the intrusion alarm from experiment 15.  All the enhancements are worthwhile, but I never implemented the system (my wife was not enthusiastic about adding the reed switches to windows and string wires around the house). So, the enhancements would be a learning exercise only. That's not bad--these are all learning exercises--but I think I've got the concepts and I'm ready to move on.

Here's what Charles proposes:

1. Delayed activation
   Use a 555 timer mounted in a separate box with a button to activate the circuit and the 12V power to the alarm passing through it. Before leaving the house (e.g.) you push the button, activating the circuit which cuts the power to the alarm for 30 seconds. That gives you 30 seconds to open and close the door (which in this case has the reed switches) without triggering the alarm,  After 30 seconds, the power to the alarm is restored and the next time the door is open the alarm will be triggered.
2. Keypad Deactivation
   In experiment 15, once the alarm is triggered it makes noise until the power is cut.  By adding a latching relay and keypad system a la experiment 20, we can turn it off without cutting power
3. Delay before deactivating
   It would be nice to have some time when entering the house before the alarm sounds.  The solution here is to add another 555 circuit, in bistable mode.  This is interesting, becuase in addition to using the threshold/trigger mechanism, it is necessary to be sure the the circuit starts and stays going without being reset, so there is a smaller capacitor on the reset pin to make sure it starts LOW (output inhibited) and becomes HIGH (output allowed) faster than the output is triggered.  If we did not do this, we're leaving it to a 50/50 chance that the output is H or L. This feature allows us to control that.

A worthwhile exercise, but I'm ready to move into Chapter 5.

@MAKE Electronics Experiment 23: Nice Dice

This is an interesting and challenging experiment. Challenging because I sometimes have problems getting from schematics to breadboards, and I always have in the back of my mind that I may have cooked a chip.  No cooking this time, just stupid wiring tricks.  But, I got it to work.

We started with a 555 timer to send pulses to the a 74LS92 counter chip and 3 LEDs to count from 0-5 in binary, Note that the LSs are TTL chips as opposed to the HC CMOS chips we've been using.

Since the idea is to emulate dice, we need 7 LEDs, one for each dot on a die. We did that by adding a 74LS27 quad-gate triple input NOR chip, along with 4 diodes too protect inputs from flowing back into outputs.  In this version we had low-current LEDs tied to GND through 4.7KOhm resistors. This LEDs were not too bright (like me). By connecting the middle dot, to one output. each of the to diagonal pairs to 2 more outputs, and the two middle side LEDs to another, we were able to produce 7 combinations from the 4 outputs by connecting thim. The middle lights on 1, 3, and 5.  The middle sides light on 6 only.  One diagonal lights on 2, 3. 4, 5, and 6, and the other lights on 4, 5, and 6.

Next step was to add an inverter.  In the previous set up, the NOR chip needed to power the LEDs, What we want is for it to sink power, but to do that we needed to reverse the logic.  We used normal LEDs connected to power through 100Ohm resistors, and connected the inverter outputs to the negative side if the LEDs.  This was much better, because the LEDs are much brighter. 

Making the right connections from the NOR to the inverter to the LEDs turned out to be a challenge, but I stuck with it.

Finally, I replaced the 10uf capacitor between pins 7 and 8 of the timer with a .01uf, making the lights flash 1000 times faster and the change not visible (to me, at least).

So, you hold down the pushbutton and all LEDs appear to be lit. Release the button, and you have a roll of the die. Nice dice

Here's the video.

@MAKE Electronics Experiment 22: DeBouncing and Flip-Flop

This experiment is deceptively straightforward. The only issue I had was a bad chip.

First, I mentioned in the last experiment that the slide switch was not breadboard friendly.  The pins are not long enough and with only one row of pins it's not stable. I tried taking it apart with the intention of making a breakout board, but that proved to be harder than it should be (I should have left it together).  So, I went to Radio Shack and found this. The advantage is that it's a DPDT and  has 2 rows of pins, making it more stable.

So with a better switch, I tackled the experiment. Both circuits do the same thing. Debouncing means ignoring errant button pushes. Since latching logic gates set in the first impulse, anything further is ignored.  We latch by feeding the outputs of each gate to one of the inputs to the other.  The second input is connected to a pull-down (NOR) or pull-up (NAND) resistor and to one side of the switch. The pole of the switch (we only use one) is connected to Vcc (NOR) or GND (NAND).
Each output also powers a low current LED when it's HIGH.

NOR output is LOW unless both inputs are LOW.  When the switch is towards a gate's input, that input goes H, making the output  L. That gate's LED is off, and one input to the second gate is L. Since the switch is away from the second gate, that input is also L, making the output H, turning on the LED and making one input back to the other gate H, keeping it's output L and it's LED off. Switch to the other gate and one input goes H, making output L  and both inputs to the other gate L and it's output H and LED on.  It can only be in one state or the other. Debounced.

NAND works similarly.  NAND output is H unless both inputs are H.  The switch is connected to GND and each gate has 1 input connected to a side of the switch and a pull-up resistor. So, one input is H unless the switch is closed to that side, in which case it's output goes H,turning on the LED and feeding H to one input of the other gate.  Since the switch is open to that side, it's pull-up resistor makes the other input H, making the output L, turning off it's LED and feeding L back to the non-switch input of the other gate, keeping it's output H until the switch is moved (or power to the circuit is cut).

Fun and interesting. Here's the video.

@MAKE Electronics Experiment 21: Game Show Button Controller

After the last experiment this one is pretty straightforward. One 74HC32 quad OR chip, 2 timers, one SPDT switch, 2 tactile buttons, 2 LEDs, 3 10K resistors, 2 330 Ohm resistors. The wiring's the thing.

I couldn't get it to work at first, but it was just a loose connection. That, and my "breadboard-friendly" SPDT slide switch wasn't so breadboard friendly. I had to bend up the tabs on the side to get it to fit the breadboard at all, and the legs still weren't long enough. But it works.

Anyway, the switch is for Art Fleming to activate and deactivate the contestants buttons.  The buttons are tied to Vcc through a pull-up resistor. A jumper from one side of the switch to the side of button 1 1 not connected to Vcc and then a second jumper from there to the corresponding button on button 2. The other side of B1 goes to OR Gate1, input 1. The same for B2, the corresponding side goes to OR Gate 2, input1.  Both input2s are connected to Gate3 output. Gate3 inputs are connected to the output pins of the 555s.

So, in order for the output of either 555 to go H, the input on trigger pin 2 must be L. The trigger pins are tied to the outputs of OR Gates 1 and 2.  OR output is H if either input is H.  One input is tied to 555 output, which is L until triggered by it's corresponding OR Gate. Button outputs are H if no action is taken, so the 555s are not triggered. When a button is pushed, the voltage from the button goes negative, making both inputs L, and the corresponding output L, thus triggering the corresponding 555 output. Both 555 outputs are connected to LEDs, so the LED lights and stays on until reset.  Once one 555 output is H, Gate 3 output is H, and neither button has any effect because the corresponding outputs will be H.

When Art Fleming activates the contestants buttons and asks a question, the first contestant to press the button lights his/her LED and locks the other contestant out.  The other side of the slide switch is connected to the 555 reset pins (4), so when Art slides back the LED turns off.  When he's ready for the next question, he flips the switch back and the cycle repeats.

Here's the video.

@MAKE Electronics Experiment 20: Keypad Security System Epilogue Part II: Making it Work

Getting past the fact that the 555 won't supply enough voltage, ever, the next question is how can we amplify it. The answer is with a transistor.  It took me way longer than it should have to get it to work, because of wiring problems and cooked transistors.

First the wiring:  instead of taking 555 Output Pin 3 to the + side of the relay coil, I connected it to the base pin of a 2N2222A transistor (NPN BJT).  I then connected + side the relay coil to the 5V rail, and the - side of the coil to the collector pin of the transistor.  The emitter pin goes to GND. Initially, I left the LED in the circuit, but since that's connected to GND, the circuit was always completed. I'm sure there's a place I can put it, but it works without it.

After few wrong connections, I still could not get it to work. I was absolutely sure that it was wired correctly.   During this process I must have cooked a transistor or two, In desperation, I replaced the transistor again, and it worked.

So, that's the answer:  insert a transistor, properly wired, and the voltage that was too low to trip the relay is enough to activate the transistor, allowing 5V to flow from the 5V rail through the relay to the collector, and when the 555 is triggered, the output pin will supply enough voltage to the base pin of the transistor to allow current to flow through to the emitter, completing the circuit.


Here's the video

I'm glad I got this to work.  I hate to leave something incomplete..

@MAKE Electronics Experiment 20: Keypad Security System (Epilogue--May be the Book's Fault!)

As I noted that 555 Output Pin 3 voltage will be lower than the Vcc on Power Pin 8 by up to 1.7V.  That probably should have been the first thing I checked, but...  Anyway, I was puzzled by this--how can we flip a 5V relay if we design a 5V input into a chip that cannot put out 5V.  I went the book page on the O'Reilly website and got this response:

Your Errata Submission for Make: Electronics

arduino

x

booktech@oreilly.com	11:53 PM (10 hours ago)
to me, plattland

Hi Virgil Machine,

Thank you for submitting errata! The author of Make: Electronics, Charles Platt, has written you the following response.

------------------

I think you're right but I am traveling right now and do not have a copy of the book. I will try to address this soon.

------------------

We appreciate the time you took to write.

Kind regards,
O'Reilly Customer Service
--
O'Reilly Media, Inc.
http://support.oreilly.com

--------------------------------------------

Your Errata Submission:

Type: Serious technical mistake
Page: 200
Location: Questions, 1st paragraph
Description:
Many have had trouble getting the relay to activate due to insufficient voltage. This paragraph says that the reason for using a 555 was to deliver enough voltage. However, according to Charles' Encyclopedia, Vol 2, the voltage on the output pin will be up to 1.7V less than the input.  Since input is 5V, and that's what the relay needs, how can that be? In my case, I'm giving 4.86V to pin 8 and getting 3..77 volts on pin 3.  Is this an error or am I missing something?

So, this may be a dead end.  I have to figure out how to increase the voltage...one person reports having success with a transistor, but I can't get that to work--I may not be understanding his wiring directions. More learning to do.

@MAKE Electronics Experiment 20: Keypad Security System (Part III--still not working)

This has taken a while. Snow, family visiting, setting up my new generator, an fuel oil spill in my basement, and other events have dominated my attention.

When last we left this, I was convinced that the keypad was sucking current from the circuit. I used this one.  The only videos I've seen of people getting this to work use momentary buttons instead of the keypad, I tried to substitute buttons--that didn't help. Testing various locations with my meter, I see that's not the problem

I checked the voltage coming into the first part of the circuit, and then then through the operation. I put a meter set to continuity connected to the relay. If the upper coil on the relay gets 5V, there should be continuity, and 5V to the lower coil should reset it. As you can see in the video, holding the '*' key and entering the code causes the indicator light to turn on for ~1s as designed, but the relay does not flop.  The voltage meter shows <4V coming out of the 555--not enough for the relay. If I hit the relay with a jumper wire connected to the 5V rail, the relay flops and there is continuity until I press the '#' key or hit the lower coil with 5V,

Testing various locations with my meter, I see that's not the problem.  Here's the video.

The 555 has 4.86V going in on pin 8 and only ~3.7 going out on pin 3.  That's the problem, and I don't know what to do about it. I fussed with capacitor and resistor values with no change.  For the video, I wound up with ad 1000uf capacitor and a 10K resistor, so pin 3 would have output for longer and I could see it on the meter. I tried various combinations of 2.2, 10, 100, and 1000uf capacitors and 1K, 10K, and 100K resistors--the output stayed under 4V.

Researching, I found this web page, which says that the output on pin 3 will be ~1.7V less than the input on pin 8. Charles' Encyclopedia of Electronic Components Volume 2 says the same thing. I'm going to move on.