lørdag 22. mars 2014

First multi-sub-oscillator board populated

The first 4 x sub oscillator board has been populated. This is the top board, a second pcb with four more sub oscillators will be mounted below it. This time I've made sure connections from the lower board actually go through the top board, so no cables have to be attached to the lower board (as opposed to the oscillator boards where you have to connect cables to both boards.

This is the rev 1 board which has the same bug as the single sub oscillator, so I have soldered 100nF caps to the flip flop feedback lines to make them flip and flop like it should.

Quad sub oscillator
Close up, note the tiny 100nF caps soldered directly onto the smd components' legs.

New panels

This week I've finished five new panels and prepared prints for three more. I've done two more oscillator panels, two sub oscillators and one 7-saw controller. I've also printed two more sub oscillators and one controller. Since the edges of the first oscillator panel didn't get as sharp as I wanted when folding the plastic around the edges, I've decided to cut the foil along the edges this time.
Plexi glass panels before attaching the adhesive film

Three oscillator modules - the first one to the left has plastic folded around the edges while the new ones are square cut for a sharper edge. I've also realized that I will run out of orange potmeter caps. Unfortunately, Re'an has stopped producing these so it's hard to get more. I've found some similar looking ones on Ebay, they seem to be 1mm wider but it may work out ok.
Finished sum oscillator and 7-saw control panels

Close-up of the sub oscillator. Note the input polarity switch, setting this to the opposite of the input wave will give that cool saw-within-saw wave shown in an earlier post

tirsdag 11. mars 2014

Tiny but crucial bug fix on the suboscillator board

A couple of weeks back I populated the first single suboscillator board, but much to my dismay it didn't work. I didn't have time to inspect it further, but I suspected it was related to the CD4013 flip flop as I had some trouble getting it to work originally. I ordered some more from a different source and they arrived yesterday.

I swapped the old chip for the new one, but it still didn't work. I then rebuilt the first part of the circuit on a breadboard, and it sort-of worked, but both flip flops in the package seemed to flip and flop at the same frequency, which they definitely shouldn't.

Today, I tried adding in a 2k2 resistor between the D and not-Q ports, as well as a 100nF cap from D to ground, a trick I found somewhere online when I originally designed the circuit. This made the circuit work again.

Doing this on the PCB would require me to cut some traces, which would be a lot of trouble, especially on the SMD-based quad suboscillator.

Luckily, when i replaced the 2k2 resistor with a wire, while leaving the cap in place, it still worked :) I soldered two caps onto the pcb as well, and it too worked like it should. I have not tried the board at various frequencies, but for the time being it seems to work fine.

While searching for solutions to my problem, I came across this post named "cd4013 weird shit" - that really sums up my thoughts about this whole problem too...

The fully populated sub oscillator board. It looks a bit like a bug of sorts, don't you think?

A closeup of the 100nF capacitor. Also note the beautiful curved cutouts, I just love the boards OSHPark are able to produce!