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Topic: DIY RFID Security System Help (Flyback voltage?) (Read 1 time) previous topic - next topic

datruesurfer

Hi,

I'm trying to build a DIY RFID security system based on a post I saw on the old Arduino forum: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1267227582/24#24

I have:

Arduino Duemilanove
HID ProxPoint RFID Card Reader
SPDT Relay
Electronic Door Strike (opens on 5v, 2a of current)
5v Power Supply (powers door strike)

I modify lines 8 and 9 of the sketch to match Serial Number and Site Code of my HID Key Fob and upload it to the Arduino. When I scan the fob the strike opens for three seconds and closes as it should. My problem is when I try to repeat the process with the same fob the strike will not open unless I scan it at least three times. When I unplug the power supply for the door strike and just have the relay with nothing live attached to it I am able to scan the fob multiple times and the relay will switch on and off normally. This leads me to believe I need a diode or a resistor somewhere but I'm not sure what i need exactly or where I should put it. Can someone help me out here? I have attached a drawing to get a better idea what I have now.

Thanks!

tkbyd

If you have a relay and an Arduino connected, and no diode...

UNPLUG IT RIGHT NOW... don't plug it in again until you have read...

http://www.arunet.co.uk/tkboyd/ec/ec1relay.htm

What you need is simple, but you DO NEED it!

datruesurfer

That looks like exactly what I have. Its interesting because I have tried two Arduino's in the same scenario and they both work fine after being connected to the relay with no diodes whatsoever. It looks like I need to put the diode between the positive and negative terminals of the coil, right? Also, what kind of diode should I use?

Grumpy_Mike

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It looks like I need to put the diode between the positive and negative terminals of the coil, right?

Well right except that relay coils don't have positive and negative terminals unless they have an internal flyback diode fitted.

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what kind of diode should I use?

Normally one capable of carrying the current of the motor (peak not continuous), basically a 1N4004 will do in most cases.

datruesurfer

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Well right except that relay coils don't have positive and negative terminals unless they have an internal flyback diode fitted.


I don't understand... Here is a schematic of the relay I'm using: http://media.digikey.com/pdf/Catalog%20Drawings/Relays/ART-T70%20SCHEMATIC.jpg

Aren't pins 5 and 2 the positive and negative terminals of the coil? I know the relay will not activate unless I have both connected.

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