Hi guys:

I'm experimenting with a circuit where I'm flashing an LED at 1kHz. Elsewhere in the circuit I have an unrelated analog (AF) signal from a sensor. It is a very small signal that is later amplified.

My problem is that the 1kHz signal is appearing in the power and ends up in my analog signal. I can see it in the +5 leg with a scope. The LED pulls about 80 mA with each pulse (40 mA RMS). I have bypass-capacitored it with no luck. I also can't seem to filter it from the analog with a HPF. It's small, but so is the signal and both end up in the amplifier output. It just seems to be omnipresent.

What other reasonable options do I have?

Don

 

Supply us with a complete Schematic so that we'll have something o analyse,
along with an explanation of what the LED is supposed to do.
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