Suggest a Diode accross each relay coil (Cathode to +12V) and possibly a
decoupling capacitor say .01mfd as close as possible to PIC VSS & VDD pins.

Daryl Sayers wrote:

> I have built a simple watering system using a PIC 1684. Works well on the
> test bench but am having problems running live.
>
> I am using a 24V power pack (1A). The 24v is to power the solenoids to
> open/close the water valve. I then cut this 24v down to 12v via a 7812
> to power the 12 relays that I use to activate the solenoids. I then
> use a 7805 to get 5v to power the control circuitry.
>
> My problem is that I seem to be getting spikes (back EMF) into my
> control circuitry that is reseting my PIC. I have put a diode across
> each solenoid to limit the spike but this doesnt seem to be enough.
> I put the diodes inside the box I built. Should I put something
> right across the solenoid itself. I was thinking a filter cap. What
> sort of cap and what value should I use.
>
>         12v                24v
>         |                   |
>         |                   |
> RA1-4  |\ ULM2803           |
>   -----|  \---------+       |
>        | /          |       |
>        |/           O  -----+
>                     O  \
>               Relay O   ------+-------------//-------------+
>                     |         |                            O
>                     |        ---        Long Cable         O solenoid
>                     |        /\ Diode   +---//-------------+
>                     |        --         |
>                     |         |         |
>                     |         |         |
>             GND ----+---------+---------+
>
>                     12v
>                     |
> 24V     +--------+  |   +--------+    5v to pic etc
> --------|  7812  |--+---|  7805  |-------
>         +--------+      +--------+    |
>              |               |        |
>              |               |        |+
>              |               |       --- 200uf
>              |               |       ---
>              |               |        |
>              |               |        |
>              |               |        |
>      GND ----+---------------+--------+
>
> --
> Daryl Sayers
> Corinthian Engineering                         Ph: (02) 9906 7866
> Suite 19, 401 Pacific Hwy                     Fax: (02) 9906 1556
> Artarmon, NSW, 2064                         email: daryl@ci.com.au
> Australia                                     www: http://www.cordoors.com.au
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.

--
http://www.piclist.com hint: The PICList is archived three different
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