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simple analog to analog converter

Joshua Florian
Prodigy 60 points
Other Parts Discussed in Thread: AMC7812

So what I'm looking for is simple enough that it doesn't fall into any category clearly.

I need a very simple object.  It must have 60 different names.

Gated op amp? track and hold forever? ADC/DAC together.  Whatever.

I don't think it's an unreasonable request.  Low tech track and holds don't hold long enough. (need days, not microseconds).  There don't seem to be any conversion packages that fit the bill together on one dye.

I need a run of the mill opamp (or two) with a logic input that will hold for long periods of time.  If conversion is involved internally, 10bits is fine.  Low speed.  Like one pulse per hour.  DC measurement only.

Flabbergasted at how little support I've been able to find for something that seems like it should have been perfected in 1972.

Thanks for everyone's help

  • 0
    TI__Mastermind 46290 points

    Joshua,

    This is certainly a seemingly peculiar request...

    To make sure I've got this correct - you just want to take some analog input and periodically "pause" the analog input indefinitely, right? How many channels would you need?

    The most direct solution would seem to be an ADC and a DAC - or perhaps a micro-controller that has both. Since an integrated DAC is a rarity you might just low-pass filter a PWM for the analog output.

  • 0 in reply to Kevin Duke
    Prodigy 60 points

    That's correct.

    1 channel.

    Was hoping to steer clear of the microcontroller world. (Don't feel like coding for something so inane, overkill, too little space, too much cost, etc)

    Hoping to avoid a continuous clock as well.

    Hoping there was a one-shot flash adc/dac thing or something to that effect.  I guess there's no audience for this.

  • 0 in reply to Kevin Duke
    TI__Mastermind 44550 points

    Hi Joshua,

    Welcome to the E2E Forums!

    What would be the benefit of having a long hold period?
    If you have any small amount of leakage in your circuit, it would degrade the result. I would think you would want to accurately capture the result as a digital value right away and store it in memory where it can be maintained indefinitely!

    What kind of input sensor would you be sampling?
    If you want to look at the sensor's long-term drift over time, then you would compare the sampled results stored in memory over time. If you are trying to average and get a low-noise result, you would want to oversample the signal. What your describing sounds like extreme under sampling.

    Best Regards,
    Chris

  • 0 in reply to Christopher Hall
    Prodigy 60 points

    It's not a benefit, it's a requirement.  I do want to capture as a digital value and store right away.  Indefinitely.  I do not, incidentally, need access to the data at all.  ADC->DAC.  So it's analog on both sides.

    The sensor is a potentiometer with 3.3v across it.  I need a button that will make an op amp connected to the wiper put out....say...1.85v and hold it there until it's pushed again holding....say 2.4v 

    A mickey mouse problem that seems to have no solution short of firmware.  SMH.

  • 0 in reply to Joshua Florian
    TI__Mastermind 46290 points

    Joshua,

    Joshua Florian said:
    Was hoping to steer clear of the microcontroller world. (Don't feel like coding for something so inane, overkill, too little space, too much cost, etc)

    Understood - the micro-controller itself (I'm thinking "bargain-bin"/cheapest MSP430 that has bare-bones what we need) would probably be quite cheap but the development time, tools, etc. associated with such a development can be cumbersome. This probably wins in pure component cost when compared to discrete ADCs and DACs unless we go to higher channel counts where integrated products like the AMC7812 and similar could be viable. A more simplistic op-amp approach could probably win out though...

    You've certainly found a niche of products that doesn't really jump to my mind...It's something I will have to think on  for a bit.

  • 0 in reply to Kevin Duke
    TI__Mastermind 44550 points

    Hi Joshua,

    I'm in agreement with Kevin's assessment, an integrated solution will probably be your cheapest option, but would require some coding.

    If you wanted to avoid the coding, you could try find some kind of parallel latched ADC/DAC combination, like such:

    I'm not too familiar with any particular devices like this, so I don't have a great recommendation. I did some quick searching and the ADC0804 is the closest ADC I could come by, I didn't come by a suitable DAC.

    Hope that helps!

    Best Regards,
    Chris