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Need Help - Ultrasonic AFE
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ogden:

--- Quote from: coppercone2 on August 01, 2019, 09:50:06 pm ---I really need to try to glue two etched pcbs together

--- End quote ---

Bad idea. You really want to use double-sided PCB's. I like those with photoresist on both sides, but you may apply photoresist film on component side yourself and cover bottom with tape or paint. Perhaps you missed what I said - that I do not etch traces that goes on the bottom, I trace them on the top using wires so bottom is nothing else but plain copper GND plane you never expose to the etch.


--- Quote ---I made a new PCB and used different op, that is much slower than MCP6292, the filter side still oscillates,
ive added caps between VCC and GND and the problem still stick.

--- End quote ---

How unfortunate. I blame layout where output of 2nd opamp is close to input of first. When you short input of the first filter (r11 to the gnd) - does it still generate? Your PCB must clean, w/o any residue.
mzdenkov:

--- Quote ---How unfortunate. I blame layout where output of 2nd opamp is close to input of first. When you short input of the first filter (r11 to the gnd) - does it still generate? Your PCB must clean, w/o any residue.
--- End quote ---

When inverting input of the first opamp is shorted to the grond the whole circuit stops oscillating...
On the R11 there is small oscillation before shorting, and i think that amplifies a lot at the end.

Ive attached the new version, it aint much, but i thought that it will work
ogden:
Try to decrease gain of one or both filter stages. It may fix feedback problem and at least let you proceed further with project. You definitely shall straighten-up component placement such a way that input is on the one end of PCB and output - on the other.

Useful tool: https://www.analog.com/designtools/en/filterwizard/
StillTrying:

--- Quote from: ogden on August 02, 2019, 12:13:49 pm ---You definitely shall straighten-up component placement such a way that input is on the one end of PCB and output - on the other.

--- End quote ---

I think that half the time, but in listening mode the US transducer is the actual input.


--- Quote from: mzdenkov on August 02, 2019, 12:03:51 pm ---When inverting input of the first opamp is shorted to the ground the whole circuit stops oscillating...
--- End quote ---

Not too surprising, but if it never oscillates with just T1's base-emitter shorted I think that would be good sign.

If you''re using the transmitting signal are you sure it switches off after a few cycles.
SiliconWizard:
And what happens if you short TRND+ and TRND-?
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