# photo diode sensor measurement with ADS1232

I’m going to use this chip for Measure the output voltage of a photo diode (100 m V to 800 m V)!!!

Is it possible?

No, that 24 bit ADC is intended for low impedance sources such as bridge sensors, and requires a specially designed circuit board.

See this introduction to photodiode amplifier circuits.

what is a suitable 24 bit A/D converter chip with 10 to 100 sample/SEC for this goal?

Why do you want a 24-bit ADC? That's a very high resolution - what application do you have that would need this? Also not likely that your photodiode's output is that reproducible to come near that resolution, I wouldn't be surprised if the noise level eats up the first 8 bits of your signal, meaning you could get a just as accurate measurement using a 16-bit ADC.

I'd use a high-impedance OpAmp to buffer the signal, so you can read it with just about any ADC. To increase precision a bit you can add a gain to your OpAmp circuit, to get the maximum closer to the maximum of your ADC (e.g. a 4x gain for 0-3.3V, 6x gain for 0-5V).

wvmarle:
Why do you want a 24-bit ADC? That's a very high resolution - what application do you have that would need this? Also not likely that your photodiode's output is that reproducible to come near that resolution, I wouldn't be surprised if the noise level eats up the first 8 bits of your signal, meaning you could get a just as accurate measurement using a 16-bit ADC.

I'd use a high-impedance OpAmp to buffer the signal, so you can read it with just about any ADC. To increase precision a bit you can add a gain to your OpAmp circuit, to get the maximum closer to the maximum of your ADC (e.g. a 4x gain for 0-3.3V, 6x gain for 0-5V).

thanks for replay
my goal is turbidity measuring and range of changes is 0.01 NTU that is needed to 24 bit res.

You’re asking for a range of more than 8 orders of magnitude. What photo diode are you planning to use? Does it even have nearly this range? A response image of light intensity vs produced current on Wikipedia gives less than one order of magnitude difference. That’s not hopeful for your project.

No matter what, you’ll have to build some kind of circuit as a photo diode produces current (it’s basically a small solar cell), and an ADC needs voltage. So you must provide an appropriate load, such as a resistor, and then measure the resulting voltage.

0.01 NTU, other than that I don’t know the unit, doesn’t mean much in itself. If you mean that this should be the resolution, at 24-bits you’re looking at a range of 0-160,000 NTU.

Certainly, it should be possible. Your question is too general, what side is more troubling you - hardware or software?
For hardware I would start from data sheet, figure 44, connecting PHDiode instead of thermocouple.
Software is also should not be too complicated, interface looks similar to HX711, and internet has a lot of arduino libraries.
TI has basic firmware driver at their ftp server: