| Electronics > Projects, Designs, and Technical Stuff |
| 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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