Reverse engineering ELRO HA51 wireless

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What is it

It's a alarm system, used with wireless accessories. We have a central and a remote control:

Elro HA51.jpgElro HA51 remote.jpg

Setup

We opened the device, no internal alarm trigger's where used. The system contains 2 board:

  • Logic board
  • 433 receiver

We hooked up a logic analyzer on the 433 receiver board to "snif" the datastreams:
We opened the remote to change the dipswitches: Elro HA51 remoteinside.jpgElro HA51 remoteinsidedips.jpg

After sniffing a few times this the result:
"Put alarm off" with all dips off:
File:Elro HA51 433 alloff alarmoff.jpg
"Put alarm off" with all dips on:
File:Elro HA51 433 allon alarmoff.jpg
As you can see, the first pulse is always short, the next 8 pulses is the code of the system, dip "off" is a small pulse, a wide pulse is dip "on".