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Working on existing PCB which has reset issues. Have been able to solve all reset problems except the following: Using a PCB mount T9AS1D22-24, upon micro going low on Q3 base (K3-A coil de-energize), micro will occasionally reset.
Have attached circuit for viewing. Anyone have suggestions on how to better filter this?

Relay giving me fits is http://www.mouser.com/ds/2/418/NG_DS_1308242_T9A_0915-719064.pdf

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    \$\begingroup\$ This picture is scaled down so values are very hard to read. \$\endgroup\$ – Janka Jul 13 '17 at 15:30
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    \$\begingroup\$ You only use a half-wave rectifier to source both the µC and the relay circuit. This is very bold of you. It should work if you replace the 1000µF cap by a 10000µF one. Better use a full bridge. \$\endgroup\$ – Janka Jul 13 '17 at 15:32
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    \$\begingroup\$ Maybe you need some high frequency decoupling on the relay coil as well, some good ceramic 1uF and 0.1uF caps might help. \$\endgroup\$ – John D Jul 13 '17 at 15:51
  • \$\begingroup\$ Iupdated the image to make it easier to see the values \$\endgroup\$ – becjasl Jul 13 '17 at 15:52
  • \$\begingroup\$ @becjasl The text size for the part values is still too small for easy reading. Using dark blue on black is a bad contrast, just use black text on white background. \$\endgroup\$ – Uwe Jul 13 '17 at 16:00
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In my experience, issues with relays causing problems typically come back to the protection across the relay coil. I would try a capacitor across the relay coil. While diodes are, I believe, a bit more typical, I have fixed many relay issues with capacitors. See Protecting microcontroller from inductive loads, which looks at the difference between protection methods.

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First, check to make sure the flyback catch diode D18 is really there, not broken, and the connection intact. Without it, this is exactly the kind of symptom you'd expect, in addition to Q3 eventually getting fried.

Second, make sure the PIC is properly bypassed and that MCLR isn't floating. Make sure there is a 1 µF or so bypass cap from every power pin directly to the nearest ground pin. Note that power pins include AVdd, not just Vdd. All the Vss pins must be tied together solidly right under the PIC.

Otherwise, this is probably due to noise caused by the switching itself. The relay contacts and what is connected to them should be kept away from the low voltage circuitry. Proper grounding of your circuit will also minimize the problems caused by nearby transients.

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