Garage Door Safety Sensors

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

They are Fail safe, as I read it. Does the door close with out them hooked up? Or with the terminals shorted? They probably use the supply and load it to a certain voltage to trip the door open. Anything else would seem to add cost. Apparently they pulse the module and check the receiver. So they are multiplexed in some fashion. And one or both sensors can trip the door individually.

FYI, I looked at the Liftmaster 8550 and the sensors Liftmaster 41A4373A

Time to break the scope out.

Cheers

--Winston

This kind?

Those work via infrared. Details should be in patents assigned to companies like Genie or Chamberlain. Or hang a scope on it and let the grandkids scoot through the beam :-)

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

Some clues here "Under U.S. federal law (UL 325), garage door openers manufactured for the U.S. since 1993 must include a safety reversing system, such as photoelectric eyes mounted no higher than six inches above the ground, with a light beam spanning the door opening. The garage door opener is required to reverse the door to the open position if the beam is broken.[9] Other examples of safety reversing systems, allowed within the guideline of UL 325, include electric safety edges, which reverse with approximately 15 pounds of downward pressure, and a garage door and opener system without photo eyes, tested together, which reverses upon approximately 15 pounds of pressure.[10]" This is from Wikipedia. See:

What mechanism is used in automatic reversing power windows in cars to reverse direction when there is an obstruction?

Howard

I think they're just simple modulated IR beams with integrated IR demodulators (similar to IR remote control receivers), such as this one:

All the rest of the smarts resides in a microcontroller.

Best regards, Spehro Pefhany

(...)

Short answer: It's like a 'one wire' protocol.

Long answer: The 'transmitter' and 'receiver' are parallel-connected to a medium-pullup 5.5V DC source. The transmitter pulses an IRLED at a 154 Hz rate, 7.7% duty cycle.

The receiver (probably just an IR filtered phototransistor) receives the pulses and pulls the DC source down to nearly zero volts in response to each received IR pulse. The microcontroller in the opener decides if it is getting the pulses sourced by the transmitter.

Blockage of the light will result in a continuous 5.5 V present on the two wires. Continuous 0 V or 5.5 V is considered physical path interference and will prevent the door from closing unless the hard switch in the garage is held closed continuously.

Clever!

--Winston

I think you'll find the transmitter supplies a pulsed IR light carrier in the tens of kHz range to match the reciever.

It would be interesting to see if the carrier is pulsed or not without the receiver- too bad he didn't hook a photodiode to his 'scope. Maybe someone has this type of garage door opener and can take a measurement?

The receiver has an integrated receiver module inside. It pulls its own power supply down (and the transmitter's power supply) when the carrier is detected.

(but presumably there's a diode + cap in each module to keep at least the receiver alive for a few msec. There has to be current limiting in the base unit- maybe a zener shunt regulator and pullup to +24 or whatever.

Best regards, Spehro Pefhany

Okay. patents.

US5465033 illustrates an early higher voltage implementation that has the parallel transmitter/receiver configuration.

Looks like US6906307 is pretty much what is used now- the transmitter circuitry is in one module and the photo detector, amplifier, AGC, detector is in another.

Looks like the transmitter sends continously so long as power is applied (and the beam is not received in the parallel configuration).

It _is_ a clever arrangement- sort of a windowed watchdog timer that depends on the modulated optical path for feedback. Very, very unlikely to accidentally fail in a state which indicates an unblocked door, despite using cheapie parts in most spots (and a few redundant-for-reliability parts around the micro).

Best regards, Spehro Pefhany

I imagine that Chamberlain and Genie, etc. use different frequencies. The patent you cite (US5465033) indicates 1400 Hz in one embodiment. (Column 5, line 39, 46) So apparently they split the difference. :)

I *do* see 30 KHz tossed out as a possible frequency in US6906307, however. The pulse repetition rate does not matter, as long as the respective circuits are adjusted to accommodate it, IMHO.

I'm interested, too.

'Hardwired single-frequency RFID' is how I think of it.

The diode and cap you mention popped into my head as well.

I see they use the phrase 'one wire' to describe the design. Where did I hear that before? :)

I suspect we will find that the transmitter sends it's pulses regardless of whether the pulses are received.

At the risk of revealing the blindingly obvious, a broken wire to either sensor puts the unit in fail- safe mode and forces it to act as if an obstruction is in place. That is nifty IMHO.

Back atcha, Speff.

--Winston

Jim, go to GarageJournal.com and go to the forum 'General Discussion' and search. One fella created an 'emulator' that would replace the safety sensors as an experiment, and there are zillions of posts (OK, maybe a hundred) about these sensors.

But, that schematic will give you all the clues you need to make something up.

AFAIK there are two methods:

- detecting the motor current

- a pressure detection cushion at the bottom of the door

That's at least a start... apply a 5V supply with limited "moxie" and _watch_ ;-) ...Jim Thompson

With enough info that I can "fly" on it. Thanks!

...Jim Thompson

That clinches it. I'm "new and improving" the acoustic Doppler parking distance gadget... it's too variable to prevent the wife from parking too close to the back wall of the garage.

I may be able to use the garage opener signal as part of my scheme... if one end of that signal is at ground ;-)

...Jim Thompson

Western solution: Bolt a 2-by-4 onto the floor, with the upper edges rounded off. Done :-)

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

ide quoted text -

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

ide quoted text -

Ummm- what's the matter with using cheap as dirt parking stops

American response... visitor stumbles over hack solution, sues :-(

(And we occasionally buy new vehicles... you wouldn't guess that, since Q45 is 7 years old, truck is 11, but we do change :-) ...Jim Thompson

Paint it fire engine red and write on it "Watch your step - Ver su paso".

Easy. Drill a couple of new holes, re-arrange, patch old holes :-)