Re: Garage Door Safety Sensors

[Spehro Pefhany]

Garage Door Safety Sensors... anyone know how they work.

I'm surfing my ass off, even perusing patents, but I can't find how
they work.

Each end has two wires, black and white.

They are connected black-to-black and white-to-white, then connected
to two terminals on the motor controller.

I can't find a schematic for any portion of it.

(I'd like to simply buy a set, provide my own equivalent to that in
the door controller and use for a different purpose.)

Anyone know how they work?

                                        ...Jim Thompson
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I love to cook with wine.     Sometimes I even put it in the food.

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:
<http://en.wikipedia.org/wiki/Garage_door_opener#Safety>

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:

http://www.biltek.tubitak.gov.tr/gelisim/elektronik/dosyalar/3/IR_sfh506.pdf

All the rest of the smarts resides in a microcontroller.


Best regards,
Spehro Pefhany

 

[Winston]

Spehro Pefhany wrote:

(...)

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

http://www.biltek.tubitak.gov.tr/gelisim/elektronik/dosyalar/3/IR_sfh506.pdf

All the rest of the smarts resides in a microcontroller.

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

 

[Spehro Pefhany]

Spehro Pefhany wrote:

(...)

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

 

[Spehro Pefhany]

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.

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

 

[Winston]

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.

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.

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

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

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

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).

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

 

[Joerg]

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.

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

[...]

 

[Joerg]

Spehro Pefhany wrote:

(...)

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

http://www.biltek.tubitak.gov.tr/gelisim/elektronik/dosyalar/3/IR_sfh506.pdf

All the rest of the smarts resides in a microcontroller.

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.

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

[...]

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

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

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

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

 

[Winston]

Jim Thompson wrote:

(...)

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

You meant to say 'unlimited moxie' yes?
I agree that would heat things up a bit.

There is a 'constant moxie controller' powering
the transmitter. In US5465033 it is set up to limit
at 62.5 milli moxies.

'Works great!

--Winston

 

[[email protected]]

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

Hang a fishing practice weight (rubber plumb bob looking thing) on
monofilament fishing line from the ceiling so it lines up with the center of
the windshield (mirror mount is a nice target).

 

[Spehro Pefhany]

In my lingo "limited moxie" means limited strength means current
limited ;-)

The LM317 is set up as a current source.

Further observance shows that a supply greater than 8.2V (current
limited) is needed to see the modulation (note the 8.2V zener (D1,
SK8V2).

...Jim Thompson

Careful- I think there are at least two kinds of 2-wire sensors. One
seems to run on high voltage and one on ~6V.

Replacement parts refer to those with red and those with green LEDs
being incompatible.


Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

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

Yup, you nailed it!

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

That is possible, but it would not be as good, IMHO. More complex and
it would mean that the millisecond pulses are generated inside the
receiver so an internal failure after the demodulator could cause a
false "no obstruction" signal. Easy enough to test if someone had the
bits- just use independent current-limited* supplies for each half.

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.

Yup, only two connections to the box and no combination of reversed,
shorted, broken or damaged sensors can plausibly cause a false
positive (or cause any damage or even much stress to the bits thanks
to the current-limited supply and diodes).

Back atcha, Speff.

--Winston

* I'd build a little unbypassed current/voltage-limited supply rather
than use a bench supply neat- there's always(?) a largish e-cap across
the output terminals in the latter, and that could kill the receiver
even if the supply limits the steady-state current. A resistor and
6.2V zener should suffice for bench testing.


Best regards,
Spehro Pefhany

 

[legg]

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.

My solution was a ping pong ball suspended fro the roof. If it hit the
windshield, she's a little closer than she prefers to be.

No batteries, no wiring.

RL

 

[[email protected]]

My solution was a ping pong ball suspended fro the roof. If it hit the
windshield, she's a little closer than she prefers to be.

Or a tennis ball. A bright yellow one.

 

[Spehro Pefhany]

Which brand? My Genie uses a pair of red LED/green LED units (the red LED
being the RX and green LED being the TX).

This
http://www.amazon.com/Liftmaster-41A4373A-Garage-Opener-Safety/dp/B0006N1RH6/ref=pd_sim_hi_6

vs.

This:
http://www.amazon.com/Liftmaster-41A5034-Garage-Opener-Safety/dp/B00283XU7M/ref=pd_sim_hi_3





Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

Spehro,

Have you run across any specification that says, red/green sensors run
on a specific voltage?

...Jim Thompson

Just what I am guessing from the patents I previously referenced and
the video. One type is (from one patent and the video) six-ish volts,
but I'm pretty sure there's a higher voltage type out there.