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Author Topic: reverse polarity protection on $50 robot  (Read 2387 times)

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Offline cooldogTopic starter

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reverse polarity protection on $50 robot
« 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
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Offline Razor Concepts

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Re: reverse polarity protection on $50 robot
« Reply #1 on: December 21, 2008, 07:01:14 PM »
A diode? I just fried my mega168 because of reverse polarity  :-\
« Last Edit: December 21, 2008, 07:01:50 PM by Razor Concepts »

Offline paulstreats

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Re: reverse polarity protection on $50 robot
« Reply #2 on: December 21, 2008, 07:16:29 PM »
Just a single diode between the +5v and the power regulator should be fine

Offline Trumpkin

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Re: reverse polarity protection on $50 robot
« Reply #3 on: December 21, 2008, 09:07:16 PM »
A diode would lower the voltage though.
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Offline Ro-Bot-X

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Re: reverse polarity protection on $50 robot
« Reply #4 on: December 21, 2008, 09:30:14 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.
« Last Edit: December 21, 2008, 09:31:21 PM by Ro-Bot-X »
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Offline Admin

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Re: reverse polarity protection on $50 robot
« Reply #5 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 . . .

Offline Soeren

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Re: reverse polarity protection on $50 robot
« Reply #6 on: January 17, 2009, 09:02:54 AM »
Hi,

A diode would lower the voltage though.


This won't
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
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Offline airman00

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Re: reverse polarity protection on $50 robot
« Reply #7 on: January 17, 2009, 11:54:14 AM »
or get a schotkky - only like .3V drop
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Offline Webbot

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Re: reverse polarity protection on $50 robot
« Reply #8 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.

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