What would probably be the likely cause of the output bouncing on the lower 4 bits, bits 0,1,2,3, but has good stability on the upper bits. I'm using a junk box Pic 16f807 with one input line to AN0 which is being fed from the output of a LM324 op amp wired as a non-inverting dc gain. The signal to the op amp is coming directly from a thermocouple.
If it's do to noise why does it only bounce on the lower bits?
Pj
Lower bits are the smaller voltage detection bits, right...
It's analog noise from the opamp; digitized, the lower bits wobble.
An LM324 is a terrible opamp for this. But expect noise anyhow, since thermocouples make tiny voltages.
Use a better opamp, and take lots of samples and average.
John
Or use a better ADC. For instance, the AD7792 has an integrated amplifier, and 50/60 Hz filters. With some careful layout, it will get you 16 stable bits.
A low pass filter to reduce the bandwidth will reduce the noise, you only need dc to 0.5Hz at most.
Maybe he only needs 8 or 9 bits... not everything has to be a frick'n gold plated design y'know. Best regards, Spehro Pefhany
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