connecting multiple inputs to an adc chip?

mosquito56

Is there an easy way to connect multiple input voltages·to one output? Think of a rotary switch but electronic in nature.· All this micro-tech is new to me.
Thanx

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Mike Green

There's what's called an analog multiplexor. In your case where the output is an ADC, you're better off getting a multiple channel ADC which has a multiplexor built-in and designed already to work with the other components.

RobotWorkshop

Depending upon the requirements something as simple as a 4066 CMOS chip may do the job.

Paul Baker

Analog switches (the primitive element in an analog multiplexer) have thier own design considerations to take into account when using them in analog circuits. It's not hugely difficult, but for someone of your experience I would recommend getting an ADC whiich has multiple channels, they use multiplexors as well, but they are integrated in the chip and have already been correctly implemented for you.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

mosquito56

Sorry, my bad, didn't include enough info. I want to hook up 12 thermocouples to one op-amp and feed that to the MAX1270. Since thermocouples neeed an op-amp and at least 2 resistors I now have 12 thermcouples, 12 op-amps, 24 resistors. Each op-amp would need to be calibrated seperately. What a mess.

· I have one thermocouple working with an adc0831.

Robotworkshop, thanx, checking into cmos now.

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Beau Schwabe

Do you want a summation of all of your thermocouples? There needs to be more detail on how you want to monitor your thermocouples.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

LoopyByteloose

It seems to me that the thermocouples have a very small output·(unless they include built-in op amps--thermopiles do)·and switching between them before amplification would really reduce the quality of their information. Having all 12 on seperate op amps would provide you with better readings from each one as the losses involved in multiplexing would disappear.

These don't have to all be in separte ICs.· ADCs come in multiple channels and op amps are often provided at 4 to a package.· Computer CAD design of a board will make the wiring work.

Having an 8 channel and 4 channel ADC[noparse][[/noparse]or just one·12 channel if such is·available] makes it all contained in one or two ICs with much less loss of signal quality.· I suspect the amount of software code for reading the 12 channels will be nearly the same as using a separate multiplexing chip and only one ADC.· The multiple ADCs will store all thier readings in their·individual channel·memory registers until you get to it.· Seems like·data sampling·would be more stable as sampling intervals could be in sync.·

Sometimes parallel is really the only way to go.

You can have 4 op amps to a package [noparse][[/noparse]LM324 for example], maybe more. That just leaves you with 24 resistors. If they are surface mounted, there really isn't much to fool with.· I think that comes down to 4 or 5 ICs total, a tiny board.

You might look into Eagle CAD software [noparse][[/noparse]the free version] to put this all on a circuit board.· Assembly will get even easier.

It might be easier to write code for three 4 channel ADCs as the same code could be looped 3 times.

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PLEASE CONSIDER the following:

Do you want a quickly operational black box solution or the knowledge included therein?······

···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Post Edited (Kramer) : 3/20/2008 4:40:37 PM GMT