CoViano

Playing the CoViano. Or is there a better way of embedding an uploaded video file (perhaps with thumbnail)?

Very simple amplifier using again a LM358 and finally a BC635 to drive the speaker.

Definitely no high end audio. But it works.

Building an audio mixer with 13 inputs is not so easy and I wanted it to look nice. I came up with the idea of mounting the speaker kind of in the center of a ring-segment of resistors.

I added some horizontal 10M resistors for stability.

Next step - next jig (again printed from PLA):

This jig helped soldering the components of the tone generators a lot. After some practice I managed to solder between 3 and 4 in an hour. Compare this to the prototype!

And of course the circuit:

The CNY70 and the 1k resistor at the output were added later. I mostly connected LEDs of two CNY70s in series with 33R to my +5V supply voltage. If this was not possible, I used 68R.

The capacitor at the output was added much later. After I had soldered everything together the sound was much noisier than before with individual tone generators. So I added the capacitors. However, since everything was already soldered together this was not easy. Some are therefore really askew. But I was happy when I had managed to solder them without damaging some other parts.

For the astable use pins 2 and 6 of the 555 need to be connected. I designed a jig in OpenSCAD and printed it in PLA.

I happened to have pliers which had the perfect width for the wire to be bent for this task. Quickly, the wire was bent for a lot of these wire bridges.

I fixed the jig to my desk using adhesive putty (the yellowish dots on the bottom of it). In this way, I could easily move it to a different position and it stuck again to the desk. This adhesive putty is one of my favourite tools.

Finally, I had a lot of prepared 555s.

I started on a breadboard with the simple 555 circuit to find out roughly which R/C pairs would be suitable for the frequency range. Initial calculations using the information from the datasheet helped, too. Adding a LM358 and a CNY70 I found a way of implementing a variable gain amplifier such that the signal at the output was low enough that I could not hear it on the speaker when nothing was close to the CNY70. Choosing the 220k resistor a got some dynamics and finally saturated the amplifier. Working with square waves is easy. A sine wave would require much more work.

With the circuit being finalized, I built a first prototype. It took me more than two hours to build. But it worked. There's a video of the testing in the files section. The design was somehow resembling a piano key. However, I figured out that it would be rather difficult to implement many of it into the final circuit (output near the CNY70, supply and ground in the same plane).

So keeping basic arrangements of the components I developed another design.