Simple automotive switch circuit help


Old 08-22-09, 12:30 PM
Thread Starter
Join Date: Aug 2009
Location: Princeton, NJ
Posts: 1
Received 0 Votes on 0 Posts
Simple automotive switch circuit help

Apparently my brain is getting old. I used to be able to design simple circuits without fuss but I'm in need of some assistance with this one.
The design is to turn a simple SPDT Center off switch (aka on/off/on) into an on/on/off . The switch has just 3 poles. The center pole is isolated when "off" and the up/down connect the center to the outside poles respectively.
Can't this be done with a relay? What I have is a GPS that I would like to have battery/ignition/off . Kind of an on/auto/off if you would. Trouble is my circuit that works is charging the coil of the relay when OFF. This is obviously a problem so if somebody could help with a sketch or good description I'd really appreciate it.
Sponsored Links
Old 08-22-09, 01:45 PM
Join Date: May 2007
Location: USA
Posts: 59
Received 0 Votes on 0 Posts
It's easy with a center-off SPDT switch if you will settle for batt/off/ign. You want to feed the "selected" terminals from the power sources (battery or accessory) and the common goes to the GPS.

v From battery (always hot)
o (Top or Bottom)

o (Common) ------> To GPS

o (Bottom or Top)
^ From accessory power

If you insist on batt/ign/off, use a SP3T switch and don't connect the third "selected" terminal to anything. and other electronic part vendors have SP3T (on-on-on) toggle switches in various sizes, styles and terminal types.

Mouser toggle switch selector. Select SP3T from the Contact Form filter, and your termination style and other filters as desired.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: