As mentioned in an earlier post, the resistance on the conductive thread is interfering with the sound. We fixed this by replacing the conductive thread with flexible wires up the sides of the zip, but we really wanted to try another solution.
So we built an amplifier circuit with an LM386N chip:
There are plenty of circuit diagrams online showing how to build amplifier circuits with the LM386 chip series, but the one we used was on this site. The circuit diagram is clear enough but for some reason it too a few tries to get it working (fuzzy brain?). Here’s a Fritzing breadboard illustration of the final circuit:
Note: the chip shown here should be an LM386N! The ceramic capacitor (small blue one in the Fritzing layout) is 0.1μF (10N farad), while the other two electrolytic capacitors are 220μF. The potentiometer is 100K and the yellow wire in the Fritzing illustration is the audio input, so it should be attached to the wire that would normally be the speaker output of the Arduino.
The power (in our case 5V) and ground of the Arduino are, of course, also attached to the power and ground of the amplifier circuit. One more thing: we also added a 220μF capacitor between power and ground to smooth out the extra noise on the circuit and it makes an audible difference!
Next… to test this with the conductive thread lines to the speakers…