Sending signal from wireless keypad to door intercom - Page 1
Forum section: electronics / projects

author: Benjamin Wharton
author_rank: Newbie
timestamp: February 21, 2016, 04:37:00 am
content: Hi, I was recently asked by a friend if I could find a way to make this keypad (operating on a certain frequency -218-433Mhzapparently) send a signal to the door part of an intercom (operating on a different frequency - 2.4Ghz) in order for it to unlock the door.I'm still a beginner in electronics and have literally no experience with RF stuff, so I'm wondering if there are any simple modifications (perhaps involving buying some kind of repeater-style device) that could allow me to do this?I unfortunately don't know the name of the device, only that it came with a set of electric garage doors and the box contains the word 'keycode' and the number 14870004150. Here's an image of the device:PCB images areand.Apologies for the very vague information - I wouldn't have asked here but the friend insisted.If it's not possible for a newbie like me I'll try hacking the internals up a bit with some messy bodge wires to send a 12v pulse directly from the keypad to the relay (upon pressing two buttons together) that unlocks the door - at least that much I'm capable of. Certainly not very secure though!

author: Buriedcode
author_rank: Super Contributor
timestamp: February 21, 2016, 12:40:17 pm
content: Well, it looks like the keypad operates on 433Mhz -http://www.melexis.com/General/General/TH72012-127.aspxYou could get access to the data sent from it from pin1 of the 8 pin IC, look at this on a scope to see what kind of signal it sends (maybe a packet per keypress, or just a fixed code when the right key code has been inputted).Do you have the second part to this keypad? The easiest option would be to use the receiver of the keypad that I assume provides a pulse when the correct code is entered.. and use it to trigger the 'door part' of the intercom. That won't involve any RF, you're just having the door mechanism triggered by two devices (you can use diodes to for an OR gate on the transistor powering the door part).If not you would have to make your own receiver, which may or may not be straight forward depending on what kind of packet this keypad kicks out. There are plenty of cheap 433Mhz receivers around, but the decoding side would probably require a microcontroller. If its a fixed code, you could put the rx module and micro, inside (or next to) the door mechanism, and do the above.Whilst it seems obvious, making a 'bridge' that receives 433Mhz, decoding, then encoding a signal for the 2.4Ghz door lock and sending that is a tough job. And whilst many wireless locks use a fixed code, that's hardly secure (someone could just eaves drop the transmission, and re-transmit to unlock) so the 2.4GHz system could use encryption. But if you have access to the lock mechanism and driving electronics, all you would need is a pulse or latch.

author: uncle_bob
author_rank: Unknown
timestamp: February 21, 2016, 02:45:48 pm
content: HiOk, the problem is going to be making this secure. Do you want a setup that any jerk with $20 of parts can use to open your friend's front door? I'd bet not. The link to the door lock *should* have some security on it. If it does not, I'd get him to fix that first. Bad people *do* break into homes this way. Once you have a proper setup to the lock, you will have a "hub" of some sort involved. There are a bunch of them on the market. You then securely tie the keypad to the hub.Yes, this is a "higher cost / more software oriented" solution. I would give it some thought.Bob

author: Benjamin Wharton
author_rank: Newbie
timestamp: February 21, 2016, 05:13:55 pm
content: Thank you both for your replies. Unfortunately, as I said above I really am still quite a beginner to electronics and so anything above simple soldering and jumpers is out of the question in terms of modding the keypad itself!QuoteThe keypad belongs to an electronically-operated garage door, so the receiver will be used for that. The door came with two keypads, which is why he wanted to use one for unlocking the front gate. If he could get hold of an extra receiver from somewhere that would be ideal, though from the prices I've seen online they'll be more money than he wants to spend.I think he should just stick to the traditional mechanical lock and key for opening the gate from the outside; it's much simpler to install, less maintenance, and it doesn't attract the attention of would-be thieves who wonder what you might be protecting behind those high tech security devices. Of course, the intercom will still be on the wall, but oh well...QuoteWell, the way it works currently is that when a user presses the unlock button on the main intercom unit inside the house it sends a signal to the unit outside the house, which is directly connected to the door mechanism. The desire is to allow a wireless keypad to also allow unlocking the mechanism, by sending a signal to the outside intercom unit. I've just realised that it'd be impossible to implement any sort of secure system with this, barring me quickly becoming an expert electronics engineer in the next week or so and hacking away at one of the intercoms (not going to happen). My idea of modding the keypad a bit to send the pulse directly when a couple of specific buttons are pressed together would work but it'd be incredibly easy to defeat for anyone looking inside it.So, on reflection it seems realistically impossible to do other than by using a compatible receiver. No worries, the traditional lock/key will have to do. Thanks again.

author: uncle_bob
author_rank: Unknown
timestamp: February 21, 2016, 05:48:36 pm
content: HiKeep the "hub" idea in mind. What you are talking about doing is a very normal "home automation" task. It may not be in range right now, but this stuff gets a lot cheaper every year that goes by.Bob

author: Marco
author_rank: Super Contributor
timestamp: February 21, 2016, 06:40:14 pm
content: There are some semi-universal keeloq receivers, google for GE-RCV1, but I'm not sure it would work for this keypad. You could bodge that into either of the 2 intercom units to open the door.