Using an external ADC Chip ?

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JiM33

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Bonjour à tous.

I've been involved recently into Teensy Dev Board (using Teensy 3.1), and have several projects pending.
One of them would require to measure at least 25 potential lines up to 40 lines.
Teensy board are absolutely awesome, but unfortunately, don't allow 25 to 40 Analog inputs. Hence, i thnk about using external ADC chip.

Am i wrong ? If so, how you guys would do ?
If not, is there any of you guys who'd had experimented some decent ADC chip ? which one ?

Thanks for your feedback.

Cheers
 
Yes, you can use an external ADC chip for this. Choice depends very much on the sampling rate and desired bit depth.
 
A PCF8591 would be a good choice for a lot of purposes I would think. It has a 3-bit address space so you could connect eight of them, they have 4 ADC / DAC's so up to 32 extra.
 
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Bonsoir,

It depends on what you are trying to measure. Chips dedicated to / developed for a particular purpose are usually superior to a general purpose ADC or MCU. For example, the MCP3909 is great for multiphase power measurements, far better than a teensy can be out of the box.

So it depends much on your application. Tell us more about what you are trying to measure and perhaps we'll be in a position to suggest specific hardware for you.
 
Thanks guys for your answers.
Actually my project is about pressure detection to count falling item on a surface from the same height, using a large number of piezos. Hence with weight varies the pressure. Output should makes stats and control a sorting device.
Very similar to an electronic drum kit actually
 
Thanks guys for your answers.
Actually my project is about pressure detection to count falling item on a surface from the same height, using a large number of piezos. Hence with weight varies the pressure. Output should makes stats and control a sorting device.
Very similar to an electronic drum kit actually
 
Ok so now we have an idea what you are trying to do. This guide at Sparkfun shows how it can be done even with an arduino: https://www.sparkfun.com/tutorials/330

since very high precision does not seem to be a requirement, I'd look for a set of ADCs that allow you to sample across a wide set of input lines. I have no experience with this chip but it looks tasty for your application: http://datasheets.maximintegrated.com/en/ds/MAX11638-MAX11643.pdf

It's less than $2 at digikey each and features 8 analog inputs that are arrayed nicely on one side of the chip, ie ideal for a small PCB that you replicate 4x to get 32 analog input lines. It even seems to feature an IRQ line to let you know when each chip is ready to dump its buffer contents.

The interface is SPI, so there is some learning involved to get the chips set up, read, etc. but the teensy should have more than enough data lines to handle all the IRQ and CS lines required.
 
Sir, Merci so very much for the time you took to have an eye to my request.

Here are some points i retrieved that might interest anyone, maybe :
- To this date, the 74HC4607 can be found and allows 16 inputs; for someone who dare to measure up tu 128 piezos, it seems ok, but i didn't tested it yet; i order Texas Instrument ones, but other brand make the same device with very similar specifications (ST, Maxim, Analog Device...),
-The piezo will need a 1Mohms resistor shunt, and some experience showed while working with 5V µC, using some 5,1 Zener diode too could add some security on the captor side.
 
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