I've got an old Craftsman garage door opener, circa 1991, which works just fine despite its age. One thing it's lacking is safety sensors (an IR through-beam that when interrupted, prevents the garage door from closing). Safety sensors began to be required by law in 1993.

My wife & I don't have kids, nor do we have friends with small children, so the risk here is not great. I may eventually fix the situation by installing a new door opener that has sensors. But in the meantime, I'm wondering if a kludge can be done by adding a DIY sensor setup to the existing Craftsman.

Looking online, I found a thread on the "All About Circuits" forum where someone describes a schematic that seems it could do exactly what I want: re-purpose generic garage door safety sensors, such that if the beam is broken, the circuit could drive a relay to do something. In my case, what I want the relay to do is close a circuit (that is, take a circuit that is normally normally open, and close it). The circuit in question would be the "lock" function on the Craftsman; when locked, the garage door will refuse to close.

Thing is, I don't know squat about relays & so don't know how to hook up a relay for this circuit. I'd query the original commenter - except the thread is from 2015, and a mod has informed me the commenter (MikeML) hasn't been active since 2016, so I need to start a new thread.

So that's why I'm posting: I'm hoping some wise person can read the schematic & advise me on how to add a simple N/O relay.

To start with, here's the URL for the comment in that thread where MikeML describes the circuit he came up with: https://forum.allaboutcircuits.com/threads/wanting-to-build-an-ir-trip-wire.111150/post-859430

If you don't want to visit the thread, below is the text of that comment:

Here is the magic info about those Garage door safety sensors. Power is ~6Vdc, fed through a 51Ω resistor (see the schematic). To test your sensors, wire the Tx in parallel with the Rx. Blk-Wht wires are positive through the 51Ω to 6Vdc, Wht wire goes to 0V.

If you power them up and aim the Tx at the Rx, you should have an amber LED on the Tx and a green LED on the Rx. If you block the beam (or misalign them) the green LED goes off. You can use the green LED as an indicator that beam is not broken... Do not try this without the 51Ω resistor.

The way the Rx communicates with the garage door operator (and the reason you cannot simply defeat the safety sensors with just a jumper) is that while the Rx is receiving the beam from the Tx, the Rx pulses the Blk-Wht wire to ground (effectively momentarily shorts it) for ~0.4ms every 6.4ms.

Obviously, the garage door operator is looking for this pulse train. The door will not go down if it not receiving pulses. The 6Vdc supply and 51Ω resistor R1 is actually inside the operator. If you are testing the Rx/Tx, you have to provide the 6Vdc and the 51Ω separately.

In the complete circuit below, I'm using a 555 wired as a re-triggerable one-shot to detect that the pulses stop when then beam is broken. Pin 3 (out) of the 555 is high as long as it is receiving pulses, and goes low ~25ms after the last pulse is received after the beam is broken.

The 555 out pin 3 can sink ~200mA, so it can drive a small relay, or a big LED or ??? For power, get an old wall-wart that puts out ~6Vdc. The sensors seem to work ok on 5 to 7Vdc.

Below I'm attaching a pic showing 1) the schematic he attached, 2) a scope view of the outputs; and 3) a pic of the generic garage door safety sensors he used.

My questions: What type of relay should I purchase - the more specific, the better - and how do I hook the output from this circuit into the relay to do what I want, that is, to close a very low-voltage circuit that otherwise normally will be open? Specifically what I want to do is splice the relay into one of the two wires (black) that goes to the Lock button on the wall button assembly for the Craftsman opener. And finally,
I'd like a button I can place on the wall to reset the relay back to its default state of NO, normally open.

Thanks for any tips!

 

To reverse that old Craftsman you first need to stop the downward door travel. A broken beam and relay can do that. But then you need to reverse the door to meet current safety requirements. The door should stop downward travel and reverse to full open. So to then open the door after stopping travel you need to simulate a closure of the switch yet again.

Let's review:
Door is open. You press the GDO button (Garage Door Opener) and the door begins to close.
Half way down you decide you want the door open instead of closed. You push the GDO button again, that stops the door. You push the GDO button again and the door opens to full open position.
This is the same thing you want but using a Safety Beam (SB). Understand that the SB doesn't send a continuous beam, it sends a pulse at some frequency that I don't know. Wouldn't be hard to figure out with an oscilloscope. Nevertheless, using just a relay to detect a broken beam isn't quite so straight forward. You need some kind of discriminator to tell when the beam has been broken, electronically Push The Button (PTB), stop downward travel then electronically PTB again to open the door.

Here's my experience with Craftsman. Mine was quite old and worn. At its end of life it would decide to open or close the door on its own. This could be problematic if I had the car half way pulled in or out and the door came down. Or when away - the door opened. Tried changing the code thinking maybe someone inadvertently had the same code. That didn't solve the problem. But what became the final nail in the coffin was the chain bearing. It was so worn that the chain would keep popping off the drive gear. I replaced that but still had the problem with unwanted actuations. So I got a Genie GDO. Been happy with that. Have had a few issues but Genie has excellent customer service. They've replaced two boards on two openers. One for the main door and one for the small door.

Getting a new opener comes with many benefits. First - it's new. Far more reliable. Second, it comes with SB's. Third, if there ever is a problem Genie stands behind their products. Another feature is that modern GDO's are programmable. They can read inputs from several different remotes with different signatures. There may be good points and bad to that but I've not had any issues finding my door open unless I closed it while a cat was in the garage and ran out, breaking the beam and sending the door back open. So my recommendation is instead of trying to retrofit something that is not designed to do what you need is to purchase a new opener. Mine is belt drive and is a WHOLE LOT Quieter than the chain drive. And they're easy enough to install yourself. I've installed several GDO's in the last 20 years (not my own garage doors).

 

I've reverse-engineered a few garage door safety sensors Liftmaster/Chamberlain/Craftsmen/Genie.
Because they have a safety function, the opener needs to know the sensors are (wired) there and alive.
So the detector eye constantly outputs a steady pulse train, which changes pulse-width when an obstacle is present.
You would need a circuit to detect that and then quickly send a stop+reverse signal to the door opener. Or some industrial doors use a hose and pressure switch at the door lip to detect hitting something. Or buy a light curtain and use that.

I'm keeping my old Wayne Dalton garage door opener running for many reasons against the newer ones. Just did a recap and changed the relays for good measure. Plenty of parts for sale on eBay.

New residential i.e. Chamberlain Group openers are terrible because all the money went into the IoT feature.
The motor is a tiny 12VDC brushed motor with high gear reduction. A hamster in a wheel has more power. You wait a long time for the door to move. Yes it supports a 12V battery as UPS but can't see the mech or motor lasting.
The new openers have cellphone app/car infotainment link which requires cloud access (your WiFi) and not that reliable. The RF remote does work, to bypass it. There are multiple (myQ) recalls due to bad firmware and leaking super caps with the wall switches.
My opener has a real 1/2HP induction motor no struggle with a heavy door. No IoT. Has safety sensors but I am always in eye's view when I operate the door. Is newer better?

Major thing against running old garage door openers is their weak RF remote control security. Some were before rolling-code, just using fixed code sequences so they are not secure against replay attack. You can still buy a modern remote control and receiver though and retrofit that in.

 

Major thing against running old garage door openers is their weak RF remote control security. Some were before rolling-code, just using fixed code sequences so they are not secure against replay attack. You can still buy a modern remote control and receiver though and retrofit that in.

That's what I did for my Craftsman. About a month or so ago, I went into the garage early in the morning and found the garage door open. I scratched my head & thought, well, maybe my wife forgot to close it. But she said she hadn't. The morning after that, we found both garage doors open. They have different brands of openers - the Craftsman, built 1991, and a Linear, which must have been built after 1993 due to its having safety sensors.

We don't have neighbors near enough for their remotes to have operated our doors accidentally. I read online that even distant radio waves can cause something like this; or wifi gadgets or whatever. I never solved what happened, but I didn't like it. But I also found that Genie, which makes garage door openers, also makes a kit with a Genie remote & receiver; supposedly much more secure due to switching the code every time you use the remote (is that what is called 'rolling code?') and also having 'dual frequency, whatever that means. I don't understand it but it's got to be better than what we had. I installed these for both bays & no problem since.

As for my idea of installing the DIY safety sensors for the Craftsman, I posted the same thing on Reddit and got back some good replies on how to wire up the relay as part of the circuit. So I'm going to go ahead & give it a try. It's a bit of fun for me since I used to dabble in electronics back some years. If it doesn't work, I may eventually give in an buy a new opener. I agree though that all the fancy stuff you get these days isn't what I'm looking for - just reliability.

 

Do you have the sensors and is the circuit running on 6 volts?

Thing is, I don't know squat about relays & so don't know how to hook up a relay for this circuit.

Using that 555 circuit and a relay module.
Shouldn't need a wall switch as the circuit will reset when the beam is not obstructed.
Also possible the 555 circuit can be eliminated depending on the sensors used.
Relay Module

 

Using that 555 circuit and a relay module.

Thanks, that makes it clear.