[sdiy] Idea for DCO

[Stewart Pye]

Hi,

I've been thinking about attempting to build a VCO that has the 
integrator capacitor reset by a microcontroller. For now lets assume the 
VCO design is similar to the ASM1. It would still have the expo 
converter, but it could be built using standard (cheap) transistors and 
no tempco resistor. The expo converter is just there to charge the 
integrator capacitor. The comparator would be omitted as the discharge 
FET would be triggered by the microcontroller. The linear CV would go 
into a 16 bit DAC and the micro would calculate time period required for 
the reset pulse.

There would be a timer interrupt keeping track of the capacitor reset 
timing. In the background you sample the ADC, convert it to the value 
needed to be loaded into the count register and keep storing the value 
until it's time to reset the VCO. When it is time to reset the VCO you 
take the timer reload value of the last sample and put that into the 
count register. So the next cycle will have its period determined by the 
last ADC sample taken.

Has anybody tried something like this before? Am I missing any obvious 
flaws in this scheme.

Regards,
Stewart.