Wiegan outputs question
T Chap
Posts: 4,245
I am just getting into some secure methods of access control, Wiegand being the simplest lowest cost method to start with. Several companies tell me I cannot connect 2 keypads/reads to a control input but I am doing it and it works. I can understand if the keypads were push pull D0/D1 outputs so you wouldnt want one keypad forcing a voltage on the other keypad output. Anyone ever seen a standard for these outputs to know if they are working for me in parallel because they only pull down? Seems like there would be damage pretty quick if both keypads in parallel are pushpull.
Comments
Wiegand signals are open-collector/drain like I2C. I've used the P1 to monitor Wiegand signals in the access control systems used in and around Los Angeles. As long as the two keypads / RFID readers aren't used at the same time you should have no problems. Even if both are used at the same time, you'll just get garbled data which, hopefully, the access system will filter.
In my simple tests I connected the P1 pins to the D0 and D1 lines with series (4.7K) resistors. I had a test system on my desk for months that never had any problems.
Wiegand inputs and readers are usually 5V pullup on the D1 and D0 lines, transitioning to Gnd to signal a 1 or 0, so no realy harm done so long as the drive circuit on the reader is strong enough.
Access control companies will tell you not to do it but it's almost industry standard to wire two readers together like this so long as you don't need direction of travel or antipassback.
But Wiegand is inherrantly insecure as it's not encrypted, just plain binary and very easy to spoof.
OSDP Readers are much better, and can be encrypted but that will take more work.
Many years ago I constructed a Wiegand to OSDP converter with a Propeller 1 so it is well within it's capabilities.
Thats good news guys! I was hoping to hear this. This is not a high security application but they want a FOB so thats what I a doing. I found a standalone Wiegand controller that lets you swipe a master card, then swipe a new FOB, then swipe the master card again to enter the FOB. To delete, Swipe master twice, then FOB to delete, then master. Or while enrolling a new FOB you can type in a User ID from 0 - 988 then you can delete the User ID just as easy. This system makes is very easy for the end user to add or delete people without my help.
As for encryption, I bought a $12 dollar cloner on amazon you can read a fob and clone it in 5 seconds. So I agree it is simple to steel a FOB. But as for finding a way to connect wires and sniff out the data while someone is pressing a number thats a bit more involved. The system can lock out bad attempts for any length of time so trying to type endless numbers is not simple. In the future I'll look at OSDP for sure.
Thanks