I have a video up on youtube of this working, it is based on a ramp counter, constant current linear ramp with comparator. I used an STC89C52 running at 20Mhz in 6T mode, this is based on the old 8051 microcontroller. With 20x4 LCD
Think of it like a CR timer, C x R = T (time to charge) but instaid of a curved ramp you get a Linear ramp because I = is a constant current.
where R = V/I
then you have C x R = Time.
Sorry i can't give values but thats my secret sauce, being one of the very few to pull off a home built 14bit adc.
if you have a signal generator, then use that to enable / disable the ramp at the input to R2 in my sketch. or just pull low to start ramp and pull high 5V to stop ramp.
Thanks. I guess I was on the right track then. I think commercial ADCs generally have an error that exceeds 1mV... so there is no shame in chasing 3mV or 4mV dragon.
And I guess you are in good company. Your Ramp Generator circuit resembles this one:
thanks, this is loosely based on a 1954 ramp counter principle.
begin, relese clamp start linear ramp charge, start For loop count, in the loop poll to detect comparator if not detected count increments, when comparator change detected stop count, display count value - reset counter and clamp ramp. repeat process.
the more linear the ramp is, the more accurate the ADC becomes.
Thanks for sharing the schematic. I am assuming that while Ramp control is 0V the capacitor charges and when the comparator trips it is detected in software... so my question is... is the ADC value obtained by a counter that runs during the capacitor charge cycle? Or am I completely misunderstanding your design?
but it is awesome to make and understand how these work, hp/agilent/keysight etc started out with dual slope adc and now have things like multislope or way more complex algorithms to significantly improve accuracy, how repeatable is your design both in accuracy and stability?
you should be able to find old schematics and descriptions of the older HP bench meters if you want to understand more about auto cal etc.
Is it just for fun or do you need it for something ?
I've seen people do similar things when they need an unexpected ADC and only have IO pins available. But they don't get very good results with standard pins and the processor supply for reference.
Is it just for fun or do you need it for something ?
I've seen people do similar things when they need an unexpected ADC and only have IO pins available. But they don't get very good results with standard pins and the processor supply for reference.
