Discrete Analogue to Digital converter

That sounds cool. Can you post a picture of it or a schematic or do you have a question about it?

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

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.

i'm chassing the 1mV dragon.

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:

https://incbtech.com/circuit-bench/285-ramp-generator-cb392e.html

Of course yours is preceded by a micro and doesn't rely on 60Hz like this one does.

Constant current linear charging of a capacitor over time 

Thanks, I will simulate your circuit to see the voltage ramp to satisfy my own curiosity.

Go for it.

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. 

Knighthawk_140 said:

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.

That's the part I don't get. Why post an experiment on a public forum, and then not share part of it "because secret". it's an ADC. What's the value of keeping this secret?

Hello,

This took me 10 days to figure this out, so I give a 10 day challenge to evey one.

I have just one more thing to see if I can make this rock solid

A challenge would need a more detailed spec:

• Integral non linearity
• Differential non linearity
• Noise
• Temperature drift
• Sampling rate
• Gain error/drift
• Offset
• Calibration interval

It's quite acceptable for any of these parameters to be unspecified but if you don't pin down some of them it's not much of a challenge.

For example - in your design schematic the current source is unlikely to be very linear (see TI document SYLT768.pdf).

Too busy right now to have a go but if I do I'll tell you when my 10 days start 

MK

This was just a diy build in my flat at weekends and evenings, I don't have an environmental chamber in my front room, i was seeing if it was possible to get a 14bit adc stable and fairly linear. If you analyse my video below you will see what I have achieved 

This was just a diy build in my flat at weekends and evenings, I don't have an environmental chamber in my front room, i was seeing if it was possible to get a 14bit adc stable and fairly linear. If you analyse my video below you will see what I have achieved 

Good Morning on this lovely Sunday, here is my ADC ramp in glorious 4K

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RE: Discrete Analogue to Digital converter

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