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Hi.
I'm trying to read directly from a PIR sensor (3.3mVpp) using a PIC.
I read in Microchip AN700 it's possible using Delta-Sigma Converter to increase resolution (to 20 bits !!!!) then sense small signals, like this one.
How i can do that? I'm a little confused...
Äh,
flux-compensator ?
Sorry but i don't understand... ???
I have used a pic and a cs5524 (24 bit a/d ) this uses shift in / out commands. I had 19 bits efffectivly. Remember your input circuits need to be layed out carefully to take advantage of available dynamic range.
regards
leonel, have a look at the MCP355x series of Delta-Sigma Converters. I have done some work with the MCP3553 and am planning on incorporating into a new design. They are fully differential and the MCP3553 has a 16Ms. update rate. The series is made by Microchip.
Dave Purola,
N8NTA
Using MCP3553 probably will work, but my circuit is to be supplied with 4 batteries of 1.5V, +-700mAh. MCP3553 has 170uA of current supply it's a little too much.
I would like to have a consume of about +-20uA.
leonel, In shutdown mode it only draws 1 uA...... In sleep mode it only draws 10uA......
Dave Purola,
N8NTA
You're right Dave. I took a better look after, and i read what you say.
Probably i will follow you're advise, but first i will see if there are another cheaper solution... (but i don't think so...)
Thank you.
Have you thought of amplifying the sensor's output with an op-amp before you feed it into the A/D?
A gain of 1000 isn't hard to do with one or two stages. Your 3.3mV p-p would then be 3.3V p-p.
yes, i already thought... It was my first solution.
But micro-power opamps are expensive, and consumes a little more than MCP3553.