So I have a door entry wiegand keypad (12v) that connects to an Arduino.
The Arduino is then connected to 3 latch relays (EA2-5 T) these are 5 volts and the Arduino only gives out a HIGH for 20 milliseconds to set the relay (this will then activate a door strike (I have added diodes across the door strike) for 10seconds [12v]).
delay(20); //pulse latch relay to open door
and 10 seconds later the Arduino will pulse a HIGH for another 20 miliseconds to reset the latch relay and lock the door.
I connect the coils of the latch relay direct to the Output pins of the arduino. (I do use diodes across both coils).
I have used these latch relays with Arduino for many years without any problems. They have saved me from messing with transistors and resistors to protect my Arduino as I thought the 20 milisecond pulse put very little strain on the ardunio vs 10 seconds. Less components to solder.
I use a 12v adaptor which powers the key pad (12v), powers the electric strikes (12v) and the Arduino can handle 12v so I just power it with that!
The problem is not with the arduino –
I moved this exact setup to a photon. (Swapped out the Arduino)
The photon will only accept a max of 5v – fine, so I used a 7805 to bring it down to 5v. I did not bother to use the 2 capacitors across Vin and Vout of the 7805.
Everything seemed to work well for a few minutes – then the 7805 de-soldered itself it got that hot. I found out I should never leave those capacitors off!
A bit later I found out my Photon was also fried! I put it down to the 7805 failing and giving out more than 5v perhaps. I read up on buck converters and ordered some.
The next day I braved it and used my second photon – not taking risks I decided to power through the micro usb and use a 5v power supply.
Disaster, second photon fried! – But why??? Any ideas?
Circuit worked well for a while.
As I was using 2 separate power supplies I knew I had to tie the negatives together or the wiegand serial would not work. There are 2 GND pins on the Photon and I used both of them. I noticed the way I had wired it one of the GND pins was acting as the negative for all of the door strikes, could that have damaged it?
Are the 2 GND pins common?
(can’t afford any more fried photons. Can I place an ammeter between the pins or something to try and track down the problem? also, I think 1 of the negatives broke off the 1 latch relay, not sure if that could have caused it. The arduino could open that door but the photon could not, the other doors were fine.