Garage door opener safety sensors

[Disco]

How do those safety sensors work? They usually have two wires that connect to both units - transmitter and receiver. These wires must carry the power to the sensors and the signal back to the main unit. I don't want to disconnect them, I just want to understand how they work so I can trouble shoot - The only way I have found is to install a new set to see if thats the problem - any way I can see a signal on the wire?

[bodgy]

First off I have to say I haven't first hand knowledge of Garage door openers but here are a few things that could be used to sense whether the door has reached either of its limits.<p>A Limit switch - works exactly like a momentary push button switch, just has heavy duty contacts/insulation and normally a longer plunger.
Lifts use these.<p>A Micro switch - works similar to above<p>First two options the cheaper options<p>A Hall Effect sensor - senses a magnet on the door<p>A proximity sensor - unlikely, though these are used on auto gates.<p>Infra Red - possible, not sure this would pass a safety test without additional circuitry<p>I'd go with a simple switch affair. Also if the door opener is going towards the Rolls Royce model, you will find it has a current sense resistor or device on the control board, so when the door reaches the stop the motor will draw more current that will trip the current sensor and switch power from the motor.<p>colin

[Chris Smith]

Lots of child safety switches on garage doors [federal law] are infra red detectors. <p>Any one in the way of the door closing stops the door from dropping on them. <p>This is to prevent children from being crushed, as well as not so smart adults.

[bodgy]

Safety devices take all the fun out of life <p>In the UK some years ago someone successfully sued Vauxhall (GM) for not having a written warning in the manual that if a child sticks its fingers in the car window opening while pressing the power button, kiddie winkles fingers will get crushed.<p>SOAP BOX/ RANT ON<p>Says a lot for the intelligence of some adults, and just proves that people as a society, are becoming lazy in applying brain power and experience to situations, and rely on other people do to their thinking for them.<p>SOAP BOX/ RANT OFF <p>colin

[Chris Smith]

Too many children over here ended up as half lings by our brutal heavy swinging doors. <p>You should see the swinging iron gates that don’t require sensors! <p>If the gate don’t get you the motor will cut you in half!

[haklesup]

The transmitter is a lamp of some sort. It may be infrared or it may be plain white light and a lens. The reciever is a photosensor sensitive to the light from the transmitter. The TX is simply aimed at the RCVR or the door won't work. If the beam is broken, the logic circuit turns off the motor and/or reverses the door.<p>An additional force sensor should also be installed in the gear box so that if the door encounters resistance (your car for example), it will reverse. Procedures for adjusting and testing both of these should be in the manual.<p>If the beam is infrared, you can get these little plastic cards (from radio shack among others) that will glow when held in front of the beam. you can use it to confirm functionality of the transmitter.

[unknown_entity]

Hmm, reminds me of the time when somebody at work shut the bay doors an one of the vans. The only thing that stopped it was the overloads on the motor.

[Bernius1]

My experience with those sensors is that if they
are off by .2 seconds of arc, the "check" LED on
the side will light, but the door will not close.
On my death bed I probably will remember those lost 20 minutes of life. Bodgy, I like your entry. Sort of like...
REM attempt communique
{DO WHILE}
engage in witty banter
file in lost cranial memory block
{GOTO}
bathroom
{RETURN}
{GOSUB}
sandwich
{CLS} (as opposed to'C.R.S.')
END

[keymaker]

I Just, toak hose CLAMp fac,ed therme TOGETEHR THAT WAY,
and
BUT I WODNDRED WHY DIDNTL SPLICIGN THE WIRES WORK<<<<

[bodgy]

Er Keymaker has your grasp of English or American temporarily deserted you? <p>I couldn't quite get your point - but it could be due to the 2 glasses of wine I had earlier! <p>colin

[frhrwa]

Hey Keymaker... I want some of that stuff...

[keymaker]

Jesus
Sorry about that<p>I really am curious to know why facing them worked but splicing the wires wouldn't,, because it would have worked really well I was going to put a jumper on at the terminals if it worked<p>Would have been so much easier

[haklesup]

Keymaker- good to see you're feeling better :p <p>Shorting the wires for the reciever might work but it may also want a load, experiment with a resistor or diode if a simple short dosen't work. Leave the transmitter leads open because all that is a voltage source for the light (beam)<p>The oldest openers only have the force sensor, next came incandescent lamps and finally infrared LED (less prone to false triggering by stray light). Some may use IR laser but I doubt it. <p>If the IR LED is modulated (like in a remote control) then you may not be able to tamper with the reciever. You may be able to couple the transmitter and reciever through an opto coupler but that's just a thought, try the simple approach first.<p>I expect that manufacturers would have a motivation to make systems that are tamper resistant because it limits their legal liability. Just don't tell your insurance agent about the mod.

[Bernius1]

OK Now the usual THEORETCAL TANGENT ! If you sense across the terminals, send & receive, for voltage; first DC, then AC; & if DC volts reads 66% of AC volts (NO, not auto-ranging!) ,does that prove a SIGNAL,vs. a DC VOLTAGE ???????
( AC range says 2v, DC says 1.35v)