Elro Home Control dissected

By Jasper Janssen on Friday 22 October 2010 01:13 - Comments (6)
Categories: Elro, X10, Views: 7.391

Today I found the package containing the special bits:


I immediately started unscrewing stuff, and I have some interesting results. First, the Elro Home Control set, found cheaply at almost every DIY store in the Netherlands.

Elro Home Control

As you can see, the transmitter has 5 dip switches to set the address, and controls 4 channels. The receiver has a 10-position dip switch, the first 5 must match the sender, and the last 5 control the 5 available channels (except that the fifth isn't available with this sender).

The configuration with separate dip switches for the channels A through D implies that a receiver could be set to receive multiple channels -- this is not the case. Setting multiples just causes the receiver to not respond to either.

Let's open them up. The sender has three phillips number 1 screws, the receiver has two screws of the previously seen security-slotted type, and once it's open the PCB is fixed with another small phillips head screw.

Elro Home Control opened

Overview. Note that this resembles the other sets we've seen in many ways, but there are a lot more discrete components, especially in the receiver.

Elro Home Control AfstandsbedieningElro Home Control Afstandsbediening rearElro Home Control sender IC

In the sender, we see an unmarked DIP18 IC and connected to it the 5 pin DIP switch each switch will, when on, pull one of the IC's pins to ground. To be exact, pin 1 through 5 are linked to switch 1 through 5. At the top, we see a 433.92 MHz crystal can, an LED, and on the reverse side the transmitter circuitry. Just one trace connects that circuitry to the controller, plus the groundplane and a 12V supply, so this transmitter can be easily modified to hook up to a microcontroller.

The buttons are not a matrix array this time, each button connects two traces to ground -- one of on/off and one of the four channels. The On trace connected to pin 12, Off to 13, and A through D connected to 6, 7, 8, and 10. Vcc is pin 18 and 9 is Ground.

Pin 17 is connected to a 27k SMD resistor and then goes up to the transmit circuit, pins 15 and 16 are oddly connected directly together through a 33-5 SMD resistor, ie 3.3 MegOhmm, and pin 14 is hooked to Vcc through a 20k pullup.

Elro Home Control receiver PCB frontElro Home Control receiver PCB rearElro Home Control Receiver subPCBElro Home Control Receiver IC

And now the receiver PCB. The hot side resembles the previous set greatly, with one of the sides of the plug being interrupted by a relay, with an overload protection device in series, and the electronics getting its juice from a fairly hefty cap combined with a resistor and a full wave rectifier built from individual diodes (but SMD/glass models this time)

This particular receiver includes a sub PCB that is connected with three pins, a marked 18 pin DIL IC, and the 10 pin DIP switch. The sub PCB houses an SO-8 SMD IC marked NB35BD 103C3, along with an adjustable coil and a bunch of SMD components. This looks an awful lot like a separate receiver module, but the only datasheets I can find on those numbers relate to ultra-low-drop voltage regulators. However, the pinout of those does not match, nor does the fact that this one is using all 8 pins separately.

I'm going to assume that it is in fact a receiver module. Pin 1 on the module connects to pin 9 on the main IC and appears to be ground. Pins 1 through 8 are connected to the first 8 pins on the dip switch, and the last two pins are connected to pins 10 and 11. Pin 12 appears to be unused. Pin 13 goes to the status LED and through a resistor & an SMD transistor appears to energise the relay coil (with a diode across it to damp the backwards currents generated by turning it off).

Pin 14 hooks to the middle of a voltage divider running between ground and pin 2 of the submodule. Probably DATA_IN.Pins 15 & 16 are connected directly together again with a this time 1M resistor. Possibly oscillator pins. Pin 17 NC and pin 18 probably Vcc again. Through a component marked L3, this also feeds pin 3 of the submodule.

The IC is marked HX2272-L2, which this time gives more joy than the small IC on the receiver module -- datasheet here. Also, the datasheet for the matching sender here -- this shoudl match the unmarked chip in the sender unit.

According to said datasheet, we've got A0-A7 on pins 1-8, Vss on 9, A8-9 on 10-11, D1 and D0 on 12-13, D_IN on 14, OSC1-2 on 15/16, Vt on 17, and Vcc on 18 -- matching exactly our inferred pinout, with the output D0 being used to switch the relay. VT is unused, and represents the fact a signal is being received. The -L2 designation means 2 data bits, of a latch type -- IOW when nothing is being received, the last received command determines the status of the output, and it doesn't turn off as soon as you release the remote button.

It should come as no surprise that the 2262 datasheet exactly matches the inferred pinout on the sender unit.

This set would seem to be an excellent source of sender/receiver modules to connect to my own microcontroller -- except they use pretty darn high supply voltages. 12 V in the sender, at least, and it's unclear what's being used in the receiver, this is something I will have to measure later. I will also have to try giving them lower ones than they get in operation so I can see if they are suitable.

According to the datasheet, the 3.3M oscillator resistor at 12V power should result in an oscillator setting of 8-10 kHz. The receiver unit with 1M should be about 20-30 kHz -- a bit low, given that it needs to be 2.5-8 times as much as the sender according to the datasheet. I haven't noticed any problems in operation though.

One interesting thing that I can predict from this dissection is that because channels A through D are actually simply more address lines on the chips, is that you can use combinations of buttons to address individual receivers. In other words, instead of A-D, you can also easily have the channels AB, BC, CD, or even ABC/BCD (ABCD is too much for single-thumb use for me) and with two-handed use you can get the entire 16 channels with this single remote. This is not something I would have considered too likely beforehand. So that's 7/9/16 channels from this really simple remote control set. If you're willing to flip a dip switch when you move from room to room, of course, that number goes way up.

I've tested this out, and it seems to work very well. You would need to do some more testing to determine if you get spurious on/off signals on the A or B lines when trying to turn on AB, for example, in your particular situation.

Volgende: KlikAanKlikUit AWST-8802 10-'10 KlikAanKlikUit AWST-8802
Volgende: Compatibility between the various systems 10-'10 Compatibility between the various systems


By Tweakers user Rowdy.nl, Friday 22 October 2010 08:12

Jasper, wath bitset is that and where did you order it?

By Tweakers user Jasper Janssen, Friday 22 October 2010 08:53

Rowdy, that's the bitset and shop I linked to near the end of the last post, a Mannesmann 100-part set.

[Comment edited on Friday 22 October 2010 09:46]

By Tweakers user BdK9001, Friday 22 October 2010 09:08

Very interesting. I'm using a Profile set, which is similar to the Elro set, except it's design is a bit more square :P I use them to turn my monitors and amp on and off, so there's no stand-by current.

Do you think it is possible to use the circuitry (which operates the relay) inside the receivers to operate the on/off switch of my computer? That way I can turn the PC on while I'm still in bed or upon entering the room :P

By Tweakers user Jasper Janssen, Friday 22 October 2010 09:56

It shouldn't be too hard to modify any of these modules to provide a simple dead switch, without any connection to the live wires, although it might take a little bit more modification to do so safely. You need a certain amount of separation so there is no arcing and no risking the 230 going into the power pins of your motherboard (which, I assure you, is almost certainly not a fun event). It could be that if you can identify the proper point to input a power supply, you can just run the receiver off of a 12V line, and avoid the 230V altogether.

Due to the nature of the receiver, however, you would have to press the on button to "start pushing the PC on button" and then the Off button to "stop pushing the PC on button". You might be able to modify that, in this case, by soldering in a different version of the 2272 chip (that would be a 2272-2, instead of a 2272-2L), but, well, then you're starting to get into fairly esoteric stuff.

One other thing I might investigate is programming an AVR chip to replace the 2272, if power supply issues can be managed so that it is a drop in or near-drop in replacement -- then you could program it with whatever functions you would want.

[Comment edited on Friday 22 October 2010 11:01]

By Thani, Friday 26 November 2010 22:14

Do you know which part genrate the AC to DC to supply the digital part of the PCB??

By Rune, Saturday 27 July 2013 10:35

Nice article! Very useful!!

I want to add a button to manually operate the device - any ideas?
I have tried to short circurt the pins on the IC, but no luck.

Best regards


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