repurposing garage door beams

[Apple Boy]

I have a pair of garage door safety beams that I would like to use as
some sort of beam detector in a project. Seems a waste to trash
these and design something new. The trouble is I can't figure out how
these suckers work!

Each one has only two wires going to it. I hooked up a 12v DC and
ground to each sensor and I got each to power up and start blinking
lights. But with only power and ground, how the heck does it send a
signal back to the computer? These are too old to be bluetooth.

I decided to hook up my logic probe to see if there was anything. No
pulses at all whether beam aligned or not.

Next I hooked up my DMM and set it to AC. Read 27v AC on each
sensor's 12v DC line. That's odd. I don't have a scope so I'm not
sure if there is some sort of AC signal being generated (but I would
like to have the $4700 Fluke pocket scope if you want to send one as
an xmas gift).

Finally I whipped out my camera to see if the IR sensor was glowing.
Sure enough it is.

I can't get these open, so I'm not sure what's inside. I already
applied Vulcan force and that failed - there are no visible
fasteners. Are these the impossible black boxes designed by NASA?

 

[Jamie]

I have a pair of garage door safety beams that I would like to use as
some sort of beam detector in a project. Seems a waste to trash
these and design something new. The trouble is I can't figure out how
these suckers work!

Each one has only two wires going to it. I hooked up a 12v DC and
ground to each sensor and I got each to power up and start blinking
lights. But with only power and ground, how the heck does it send a
signal back to the computer? These are too old to be bluetooth.

I decided to hook up my logic probe to see if there was anything. No
pulses at all whether beam aligned or not.

Next I hooked up my DMM and set it to AC. Read 27v AC on each
sensor's 12v DC line. That's odd. I don't have a scope so I'm not
sure if there is some sort of AC signal being generated (but I would
like to have the $4700 Fluke pocket scope if you want to send one as
an xmas gift).

Finally I whipped out my camera to see if the IR sensor was glowing.
Sure enough it is.

I can't get these open, so I'm not sure what's inside. I already
applied Vulcan force and that failed - there are no visible
fasteners. Are these the impossible black boxes designed by NASA?

Maybe IR transmitters like you find with your TV remote?


--
"I'd rather have a bottle in front of me than a frontal lobotomy"

"Daily Thought:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

 

[PeterD]

I have a pair of garage door safety beams that I would like to use as
some sort of beam detector in a project. Seems a waste to trash
these and design something new. The trouble is I can't figure out how
these suckers work!

Each one has only two wires going to it. I hooked up a 12v DC and
ground to each sensor and I got each to power up and start blinking
lights. But with only power and ground, how the heck does it send a
signal back to the computer? These are too old to be bluetooth.

I decided to hook up my logic probe to see if there was anything. No
pulses at all whether beam aligned or not.

Next I hooked up my DMM and set it to AC. Read 27v AC on each
sensor's 12v DC line. That's odd. I don't have a scope so I'm not
sure if there is some sort of AC signal being generated (but I would
like to have the $4700 Fluke pocket scope if you want to send one as
an xmas gift).

Finally I whipped out my camera to see if the IR sensor was glowing.
Sure enough it is.

I can't get these open, so I'm not sure what's inside. I already
applied Vulcan force and that failed - there are no visible
fasteners. Are these the impossible black boxes designed by NASA?

Both commons go together. (to ground?)
Both positives go together. (to positive?)

Whatever signal that tells the master unit that the slave (receiver)
sees the light from the master (transmitter) is superimposed on the
positive side.

Try connecting them to a supply, and monitoring the difference in the
signal when they see each other, vs when they don't.

 

[Frithiof Andreas Jensen]

But with only power and ground, how the heck does it send a
signal back to the computer? These are too old to be bluetooth.

They could be designed to run from a current-limited supply so when a sensor
detects something it pulls - f.x. 30 mA instead of the usual f.x. 10. Try
and stick a 100 Ohm resistor in series with the 12 V and measure the voltage
after it (or across - if that is easier).

 

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Any chance it could be an RF signal. Not Bluetooth , but say 433Mhz or
something like that.