ADC Chip
Philldapill
Posts: 1,283
Hey, I have a TI ADS1211P ADC chip that I'm trying to learn to use. It seems to be a fairly complicated little ADC with programable features. I've attached the datasheet for easy reference.
My first question, is about the Xin pin. The datasheet says the minimum frequency should be 500khz, 10mhz maximum. I need a data rate of about 10hz. If possible, and if it even matters, I'd like to drive the Xin with a pin from the prop. If I understand correctly, the Xin is usually connected to a crystal or resonator, along with Xout as feedback. Couldn't I just use a pin from the prop, oscillating at 500khz, to drive the clock(Xin) of the ADC? If so, would that take an entire cog? I mean, even if done in assembly, the prop would have to toggle the pin on/off at 1mhz. I'm not that familiar with assembly, but it seems this should be doable...
Second question. This datasheet is pretty extensive and to be honest, I don't have much time at the moment with midterms. Would anyone like a few of these chips? I'll be happy to send a couple(or more) for free, if you'll whip up some code to control one. These are 24bit, Delta-Sigma ADC's with a datarate of about 21bits at 100hz. PM me if interested, or just post.
Thanks guys for all the help(And in some cases, repeated help [noparse]:)[/noparse])
Post Edited (Philldapill) : 3/15/2008 3:28:27 AM GMT
My first question, is about the Xin pin. The datasheet says the minimum frequency should be 500khz, 10mhz maximum. I need a data rate of about 10hz. If possible, and if it even matters, I'd like to drive the Xin with a pin from the prop. If I understand correctly, the Xin is usually connected to a crystal or resonator, along with Xout as feedback. Couldn't I just use a pin from the prop, oscillating at 500khz, to drive the clock(Xin) of the ADC? If so, would that take an entire cog? I mean, even if done in assembly, the prop would have to toggle the pin on/off at 1mhz. I'm not that familiar with assembly, but it seems this should be doable...
Second question. This datasheet is pretty extensive and to be honest, I don't have much time at the moment with midterms. Would anyone like a few of these chips? I'll be happy to send a couple(or more) for free, if you'll whip up some code to control one. These are 24bit, Delta-Sigma ADC's with a datarate of about 21bits at 100hz. PM me if interested, or just post.
Thanks guys for all the help(And in some cases, repeated help [noparse]:)[/noparse])
Post Edited (Philldapill) : 3/15/2008 3:28:27 AM GMT
Comments
Check the application note for the counters (AN001) for details.
Do it the way all of us do it, by doing it yourself and I'm sure that we would pitch in to "assist".
It's many years since I worked with this chip but maybe somebody else has a different experience.
*Peter*
*Peter*
With the chip, I had a known 1V source. I read it with the ADC, and it was a little high. I was actually using a 10K pot to step down 30V to a 5V range, so I suppose the actual voltage was 6V, but 1V at the ADC. Anyway, the ADC was reading it high. I then increased the voltage up to about 4V, and now the ADC read it low. Any idea what is going on? When i say low, I mean like around 50mv-100mV. Any ideas?
Your test method may be flawed anyway, using a pot unbuffered into the chip is not the way to do it. Did you add a small capacitor to the A/D pin to provide the low-impedance that some sampling circuits require? For instance on the MCP3208 12-bit ADC there in the datasheet is figure 4-1 which gives details of the analog input model. There is a 1K switch resistance into 20pF, not much, but enough to upset your readings perhaps. I use a 4.096V external voltage reference with these chips, what do you use?
*Peter*
ww1.microchip.com/downloads/en/AppNotes/00688b.pdf
·