Simple Polarity Tester

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Dudley LeRoux 167,031 2 13
This tester can be used to check the polarity of any power source, and is therefore very useful when installing automotive equipment, alarm systems or anything else you can think of. Because this circuit is so simple and cheap, even frying one with an over voltage is not a big deal.


Schematic for polarity tester


Total Qty.
R111K 1/4W Resistor
D11Green LED
D21Red LED
D4, D5, D6, D741N4001 Silicon Diode1N4004, 1N4005, 1N4007
MISC1Board, Wire, Case, Probes


  1. Email Dudley LeRoux with questions, comments, etc.
  2. To use the circuit, just connect your probes to the source under test. If D1 lights up, the left most probe (on the schematic) is connected to positive. The opposite is true if the left probe is negative. If both LEDs are on, the source being probed is AC.
  3. Be careful when using this tester not to probe a source greater than about 12V.

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Simple Polarity Tester
Tuesday, January 31, 2012 3:37:30 PM
I'm wondering if you could use a selector switch, where the input is the node D1 and D2 share and each different output goes through a different value resistor and then into the node that D5 and D6 share. This would make it able to handle different and higher voltage ranges?
Simple Polarity Tester
Monday, January 17, 2011 6:28:51 PM
simple yet effective
Simple Polarity Tester
Sunday, April 13, 2008 5:23:09 AM
Excellent. Used it to sucessfully add more visible large additional turn indicator light above dash board on car.
Simple Polarity Tester
Monday, November 12, 2007 9:21:45 PM
thank u and many other good people on the web that share wat they make your polarity tester has made things eeser for me and works great thanks once again nick italy
Simple Polarity Tester
Saturday, November 10, 2007 9:59:43 PM
Nice. However, you don't need all that rectifier! Do you? Only two, reverse parallel LEDs and resistor. So it gets even cheaper and easier to fit in a plastic pen. :-) |----------|<---------| o-----////-----| |-------------o |----------->|--------|
Rick Selva
Simple Polarity Tester
Friday, October 12, 2007 7:18:15 PM
I'm looking for a polaraty tester that can read plus and mines this is to check a product when is plus or minus the unit should have to probes so when i touch it if going to tell if it can out plus or minus.
moses michael d
Simple Polarity Tester
Tuesday, September 25, 2007 10:09:12 AM
This circuit is true but i need more explanation please.
Simple Polarity Tester
Friday, September 07, 2007 10:04:32 AM
what is the probe
Simple Polarity Tester
Thursday, August 02, 2007 4:25:04 AM
Found useful but why not be design to rate voltage in case the voltage is higher.
grey hog
Simple Polarity Tester
Friday, May 25, 2007 5:45:09 PM
you crazy specify the uses! hello polarity tester duh
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