> 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: darylKILLspamci.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.

> I had the oposite, in the bench it did not work and on the final
> prototype it did!  I used separate boards, one for the logic and other
> for the relays that were activated by NPN transistors
>
>                         +12V
>                          |
>                          RL
>                          |
>                          C
> logic  >---->>---1KR-----B
> signal  conector         E
>                          |
>                         GND
>
> Francisco
>
> Martin Peach wrote:
>
> >I have had this kind of problem and no amount of diodes in any configuration
> >helped. Finally I shielded the PIC with metal and that did the trick. The
> >EMF seems to have been radiated inside the box.
> >/\/\/\/*=Martin
> >

> From .....owner-piclistKILLspam.....mitvma.mit.edu Tue Feb 19 12:03:30 2002
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> Date:         Tue, 19 Feb 2002 10:20:08 -0300
> Reply-To: pic microcontroller discussion list <PICLISTspam_OUTmitvma.mit.edu>
> Sender: pic microcontroller discussion list <@spam@PICLISTKILLspammitvma.mit.edu>
> From: Francisco Ares <KILLspamfrancisco.aKILLspamaltec.com.br>
> Subject:      Re: [EE] Power spikes reseting my pic
> To: RemoveMEPICLISTTakeThisOuTmitvma.mit.edu
>
> I had the oposite, in the bench it did not work and on the final
> prototype it did!  I used separate boards, one for the logic and other
> for the relays that were activated by NPN transistors
>
>                         +12V
>                          |
>                          RL
>                          |
>                          C
> logic  >---->>---1KR-----B
> signal  conector         E
>                          |
>                         GND
>
> Francisco
>
>
> Martin Peach wrote:
>
> >I have had this kind of problem and no amount of diodes in any configuration
> >helped. Finally I shielded the PIC with metal and that did the trick. The
> >EMF seems to have been radiated inside the box.
> >/\/\/\/*=Martin
> >