@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 - Together and Working, need to pretty it up

This took WAY too long, due to my fumbling.  Earlier posts and videos showed it working on a breadboard,  I needed to solder the components and circuit to a Perma-Proto Board, then connect the wires from the cart (motor + and -,  switches NO and GND).

Here's a top view of the working product:

Note the 4-pin connector I used to connect the 4 wires mentioned above through a hole in the Altoids tin to the circuit board.  That allows me to unplug the components on the cart to work on the circuit board if (WHEN) I need to, What look like stray wires are stubs for testing.  I'll reduce those during cleanup. The switched 9V battery holder is riding in the cover now.  I'll attach it to  the top of the tin with Velcro after I close it up.  I think I need a new Altoids tin--I kind of butchered this one making holes.

I added the rubber band around the driving wheel after the video for traction. It couldn't run on the hardwood floor without it.

Here's the video.

Stupid Soldering Tricks

There were reasons why it too so long.  I used 3 Perma-Protos. I would get it working, then something would go haywire.  I had a short someplace. I lost about a day fussing wit the power supply (see the right side of the photo above). I had been using 10uf and 1uf capacitors, but looked at the LM7805 datasheet and saw that the sample uses 33uf and ,1uf (same as in the book, p 182).  DUH. It said .33...so I chased that for a while, buit ibn the right components and still had a short.

I could not see anything wrong, so I decided to do a new board.  Worked OK for a while, but eventually wound up with another short.  I was ready to give up and just use a breadboard, but decided to try one more board.  After fussing with all kind of connections, I moved the 555 and reconnected everything pin by pin.  Of course, I started with pin 1 and the problem was on pin 8.  I had decided to use a 3-pin female header across pins 7-8 and the next row to connect the 33uf capacitor, so I could swap other values in and out to adjust the backup time (since I removed the pot).
I must have had a cross connection due to sloppy soldering under the header, because when I soldered in the cap direcly I had no  problem.

Now I was in business, but I had a couple of recurring problems.  I cleaned up some stray solder and it appeared to be OK.  It took a week, but I did it.

Finishing the Fabrication

I had everything working, connecting the cart to the circuit board with alligator leads.  I cut a 4-pin I2C cable in half to use as a connector to the cart, with the cut half to be soldered to the circuit board. I soldered the motor and switch wires to a strip of 4 extra long male header pins, and plugged that into the I2C connector. I tested the circuit after soldering each connection, and used head shrink to insulate the pins. The I soldered all the connections on the motor and switches.

What I need to do

1. Screw the Perma-Proto to the standoffs and close the cover of the Altoids tin
2. Velcro the 9V battery holder to the Altoids tin
3. Use threadlocker on the wheels to keep them from wobbling
4. Maybe screw the drive wheel to the motor (I would need to remove the motor to do that)
5. Tidy up all the wires
6. Put some WD-40 on the hinge so the tail moves more smoothly

 

@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 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 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 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.

@MAKE Electronics Experiment 18 - 7-segment displays, 4026 counters, 555 timers

Here's the latest, from +Make: Electronics. Experiment 18 uses 3 single digit 7-segment displays, 3 4026 decade counter chips (1 for each digit, chained together so they roll over), 3 555 timers to get the circuit to run by itself.

I did a video but it was too big for Blogger to handle. See it in this post on Google Plus.

After I did the video, I added another 555 (actually the other side of the 556), an LED, and some additional resistors and capacitors.  The book gives really clear directions, My only variations were using the 556 (because I thought that would be interesting), using 3 1-digit displays instead of a 3 (my 3s are not individually addressable--only 12 pins as opposed to the 28-pin version Charles used). Also, I turned on the decimal point between digits 2 and 3 just for grins.

This was fun.  I just got a bunch of 7-segment displays from ebay, and it's interesting to see how to control them through chips only--no programming,

On power up, the counter runs. You stop it and clear it, then hit the start switch, After a delay, the LED lights and the counter starts.  You the hit the stop switch to time your reflexes. I almost got there, but I had some sparks and some component is likely fried. Since I got it almost working, I'll move on.

The next exercise is using logic chips, and I really want to do that. I ordered a whole bunch of them from ebay, but not all have arrived yet, including one of the 2 chips I need for this experiment.

While I'm waiting, I think I'll get the 7-segment displays working with arduino. In addition to the 1-digit displays I have some 3- and 4-digit ones., That could be interesting.  Less clutter on the breadboard...kind of cheating, which is why I wanted to do it Charles' way first.

Update 01/26/2014:  it turns out that the only thing I fried was the LED.  I got it working again (there were a couple of loose connections, too).  I think I will go on and fuss with the capacitor values to see if I can get it to count close to real time by 1/100s of seconds. could be fun. That, and the Arduino thing.

Update 1/27/2014:  the closest I could get was replacing R8 (2K2Ohms) with a 10K potentiometer (actually a knob I took from a fried clock radio) and 22 microfarad capacitor for C2.  Spec for C2 was 68uF but all I had was a 47.  Charles said to use a .1uF (then on the next page he said 1, which I think is what he meant because he said a 10 was 10 times the value).  I tried several values from 1 to 100, and settled on 22 because that gave me the most responsiveness from the pot.

This whole thing was really interesting--using different chips in multiple configurations, playing wiht the speed of the timer displayed on the 7-segment devices, etc.