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Discrete Analogue to Digital converter

Knighthawk_140

Hello.

I have made a 14bit single slope adc

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

  • in reply to dougw

    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

  • in reply to Knighthawk_140

    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.

  • in reply to dang74

    Constant current linear charging of a capacitor over timeimage 

  • in reply to Knighthawk_140

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

  • in reply to dang74

    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. 

  • in reply to Knighthawk_140
    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?

  • in reply to Jan Cumps

    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

  • in reply to Knighthawk_140

    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 Slight smile

    MK

  • in reply to michaelkellett

    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 

  • in reply to Knighthawk_140

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

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  • in reply to Knighthawk_140

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

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