Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: cooldog on December 21, 2008, 06:59:40 PM

Title: reverse polarity protection on $50 robot
Post by: cooldog on December 21, 2008, 06:59:40 PM
i was just wondering if anyone has bothered to implant reverse ploarity protection is the $50 robot or how you would if you wanted to
Title: Re: reverse polarity protection on $50 robot
Post by: Razor Concepts on December 21, 2008, 07:01:14 PM
A diode? I just fried my mega168 because of reverse polarity  :-\
Title: Re: reverse polarity protection on $50 robot
Post by: paulstreats on December 21, 2008, 07:16:29 PM
Just a single diode between the +5v and the power regulator should be fine
Title: Re: reverse polarity protection on $50 robot
Post by: Trumpkin on December 21, 2008, 09:07:16 PM
A diode would lower the voltage though.
Title: Re: reverse polarity protection on $50 robot
Post by: Ro-Bot-X on December 21, 2008, 09:30:14 PM
Quote from: Trumpkin on December 21, 2008, 09:07:16 PM
A diode would lower the voltage though.

Not a biggie if you power your board from a 9V battery and servos from a separate 6V battery. If you power everythig from a single 6V battery (not gonna work with the regular 7805 voltage regulator), then the voltage drop over the diode can make your microcontroller reset when servos start/switch directions when the battery gets a little drained. If you use a 7.2V battery with a LDO regulator, using the diode is fine => this is what I use.
Title: Re: reverse polarity protection on $50 robot
Post by: Admin on January 15, 2009, 11:19:05 PM
Use a PFET for a ~0.1V voltage drop reverse polarity protection ;D

http://www.irf.com/technical-info/designtp/dt94-8.pdf

(see top right schematic, and connect load to your voltage regulator)


That being said, I accidentally reversed power to my $50 Robot for a few seconds but nothing broke . . .
Title: Re: reverse polarity protection on $50 robot
Post by: Soeren on January 17, 2009, 09:02:54 AM
Hi,

Quote from: Trumpkin on December 21, 2008, 09:07:16 PM
A diode would lower the voltage though.

This won't
(http://that.homepage.dk/Img/RevVolProtect.png)
Title: Re: reverse polarity protection on $50 robot
Post by: airman00 on January 17, 2009, 11:54:14 AM
or get a schotkky - only like .3V drop
Title: Re: reverse polarity protection on $50 robot
Post by: Webbot on January 17, 2009, 01:35:30 PM
Or an easier solution (although not fool proof) is to use a 3 pin header for the batter supply. With, say, Gnd in the middle, +ve at one end, and unconnected at the other end. Then if you plug it n the wrong way then 'nothing' happens. Or use polarized header pins/sockets.

 Obviously if the header is left plugged in and you try to connect your 9v battery into the clip the wrong way around then it doesn't help. But better than nothing.