LTC1298 - fiber optic system

Fairuz

Hie..

Currently I am designing a fiber optic sensor, consist of emitter and detector circuitry. I am using 12 bit serial ADC -·LTC1298, LT1006 op amp·and Basic Stamp2 Microcontroller. The system is powered with 9V battery and 7805 voltage regulator. The problem that I face, when the first time I run the system, without emitter turning on, I am expecting the output display (output from my ADC)·should be around 40-60. But it happen that the initial output was around 1200. From where to voltage to my ADC coming from since the sensor suppose to detect no light? Furthermore, once my 9V supply start to decay and reaching around 6 volt, the system can work as normal.

Hope to get some advice on this matter.
Thanks so much
Fairuz

Post Edited (Fairuz) : 6/16/2008 1:04:04 PM GMT

Chris Savage

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Chris Savage
Parallax Tech Support

Fairuz

Any suggestions or possible error?

Thanks so much for assistance.

Andy Lindsay (Parallax)

It'll probably be easier to spot the problem if you post schematic and source code.

When you say "initial measurement", does that mean that only the very first measuremnt is large and the rest are normal, or does the measurement persist while the emitters are turned off?

I would recommend probing the circuit with a voltmeter. Verify that the voltage at the ADC's input matches the measurement. Also, check the ADC's power to make sure the LTC1298's power input is connected to regulated 5 V (and that the 7805 is regulating properly).

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Andy Lindsay

Education Department
Parallax, Inc.