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1  Using Arduino / General Electronics / Re: DIY RFID Security System Help (Flyback voltage?) on: October 02, 2011, 01:53:30 pm
Quote
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.
2  Using Arduino / General Electronics / Re: DIY RFID Security System Help (Flyback voltage?) on: October 02, 2011, 09:20:02 am
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?
3  Using Arduino / General Electronics / DIY RFID Security System Help (Flyback voltage?) on: October 01, 2011, 09:14:18 pm
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!
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