Post by oldcrow » Thu Mar 26, 2015 12:26 am

TL;DR FAQ:



The circuit board is 8.5" x 11" (216mm x 280mm), the size of the DuinoKit Essentials PC board the aluminum case of which settled the form factor goal for the Crowminius project.



The green things are some 3D-printed shelf clips I made that serve as makeshift pitch/mod levers. I will print better ones meant for this.



There are three LFO LEDs, two are behind the PWM pots (top middle), the 3rd shows the rate of the control osc. and is over by the pitch/mod wheel pots.



The vactrol/LDR is for MIDI modwheel action, which is kind of experimental at the moment.



The A440 reference is not a Wein bridge sine oscillator, but rather is a DDS table-lookup PWM sine tone generated on the MIDI microcontroller.



There will be USB MIDI, once I figure out how to do it. I rigged the hardware as per the V-USB spec but I am not a C programmer by trade. But, eventually.



The power supply will run on a single 12VAC, 250mA wall transformer. The power supply that does not suck mode involves the use of two 12VAC wall transformers so as to provide full-wave rectification.



The DAC is scaled to provide 5 octaves, F1 to F6 over a 4.096-Volt range. The DAC's 2nd channel will operate the filter cutoff for assignable key velocity or whatever.



I did not use ua726s as they are a pain to get and the thought of exposed parts heated to 80C meant someone would get burned. LM3046s are fine; there is a tempco resistor under the three arrays for the VCOs.



The filter resonance pot is in fact a 50K reverse-log type, but I provided for using a linear pot+resistor to cheeseball it.



Yes I will be offering bare boards. They will be $100.00. I have to correct a few cosmetic issues (mostly reversed knob and switch actions) but every part came from Digikey, Jameco, Mouser or Small Bear.



More later.



Crow

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