@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.