The IR receiver module

Hi all !
I have done some reverse engineering on the IR receiver module that comes with the smart home automation kit.
This way, it will be easier to adapt the circuit to our 220V mains.
It shouldn’t be too difficult, all we need is to change the values of C1 and R2. I will calculate these in the next few days.
In the meantime, here’s the schematic, drawn in the old fashioned way :grinning:


Hi all,
It seems that only the capacitor should be replaced by 330nF, 265V.
Be aware that this is an AC capacitor and special for this kind of circuitry.
It can be obtained by the regular electronic retailers.
I found mine at the local electronics shop.
It has a spacing between the pins of about 1,5 cm.

This value gives just enough power to the circuitry, not to little and not too much.
It was calculated by the formula 1/ 2pi.f.C.
In our example : 1 / (2 x 3,14 x 50Hz x 0,330uF) / 1000 000 = 9653 Ohm
And the current will be 230V / 9653 Ohm = 24mA.
I measured first the current through the original circuit by applying 24V to the circuit and used the formulas above to get the value of the capacitor.
I rounded off a bit.

Now, concerning the plugs, I found in my cupboard a remote switch from Philips.
I opened it and the mains plug unit fits perfectly the LittleBits IR receiver !
One drawback however, the female plug has to be glued on top of the box.
A few drops of superglue holds it tight.
Here are some pictures :

Hi @Frankje,

Thanks so much for your reverse engineering diagram of the IR switch from the smart home kit!
I finally can use the IR switch now! I bought this kit in 2014 and could never use it…
I replaced the one capacitor from 680 nF to 330 nF as you explained and it worked 100% OK.

A few years ago I bought a European alternative IR switch, a so called standby kill-switch for TV make ETM. This switch had a standard time delay after switching ON of one minute which stopped me from using it.

Today I found out that the typical USA male and female plugs could easely be removed from the original Littlebits housing.(they are mounted on a circular separable part) and that the ETM version had the same plastic parts, however with European plugs !

I mounted the ETM female and male plug parts into the Littlebits housing. Then I could not close the housing, the plug parts werer too high, appr 5 mm. Then I removed the so called kidsproof protection inside the female plug part, decreasing the height with this 5 mm.

The wiring colors were different.
input AC red
output AC black
common AC white

input AC white
output AC red
common AC black

Then I could close the housing and it worked ! Thanks Frank! :grinning:


Hi Frank @Frankje,

the IR switch is working fine now. One thing I discovered:
It switches automatically OFF after appr. 90 minutes…
I think this might be programmed in the U1 chip in your diagram, I think it is an ATTiny85 ?
Is their a possibility to remove this? :grimacing:

Hello @alexpikkert
I can’t tell if this happens due to programming.
The chip used is a dedicated one specific for IR controlling. It has 2 outputs and 2 inputs.
Perhaps this has been implemented for safety reasons .
I will try this with my IR switch. Let’s see if this happens to me too.
Perhaps someone els can test this too ?

1 Like

Hello @alexpikkert,
Indeed, I did 3 tests and always after approx. 90 minutes, the IR switch turns off.
So this is no coincidence, this was done on purpose, perhaps as safety measure.
The chip itself is a bit like this SIS-2
It has different pinning though and a SMD package.
Hope that helps :wink: