Ikea STOLPA Hack: Turn off ambient light

The Ikea STOLPA wall clock is a great clock for a bedroom as it is extremely quiet, sleek and — best of all — comes to life when you clap.

Backlight Wall Clock Ikea STOLPA

The concept is simple: The clock has an LED strip recessed into the rim of the clock that turns on as soon as the a microphone picks up a sound peek. No worries though… It doesn’t have creepy Alex/Google Home microphone but only a very simple logic board and no connectivity. We should be good ;)

There is one caveat with this bedroom clock — hold tight. The clock has three modes

1. Clock only mode. LEDs are not used at all
2. Night light mode. LEDs are dimmed when the room is dark
3. Night light + Clap sensor mode. LEDs are dimmed when room is dark. Loud noises trigger the LEDs to full brightness for 10 seconds.

This means that the only mode where the clock uses the microphone it always also uses the brightness sensor to turn on or off a dim background lighting ring around the clock. There is no way of turning this off — IKEA, why??? If you want to sleep in total darkness this renders the clock utterly useless as there is no way of having it turn on at the sound of a clap but otherwise be off.

This Medium piece will describe how to create a forth mode: LEDs always off except when clapped. Some very, very simple hardware hacking will be required but the complexity is low. Let’s get started!

Note: This most definitely voids your guarantee and I take no responsibility in any accidents that result in the modification of the clock. As only AA-batteries power the clock the risk of a fire is low but do this at your own risk!

As we need to get to the internals we need to open the case up. Luckily, IKEA has made this pretty simple.

1. Remove the six screws on the back of the clock
2. Pop open the front plate from the back plate. Use a screwdriver to open up the six clips.
3. Take off the minute and hour hands by pulling them with your hand. It’s a simple orthogonal movement pulling away from the face of the clock
4. Unscrew a final screw at the center of the front plate. Take a small screw driver and lock into one of the two indentations. Then turn like a normal screw. This guy was fastened fairly tight on my clock so give it some umpf!

Steps to take apart the Stolpa

We can now see the internals which turn on/off the lights. The clockwork is on the other side in the enclosure with the batteries.

The top round metal-looking thing is the microphone. The bottom small LED-looking thing is the brightness sensor.

As we basically want to trick the sensor in always sending a signal that it is bright outside (then the LEDs are completely off) we simply need to find out what the threshold of sensor input is. In my first experiment I just short circuited the electrical connection past the brightness sensor. The lights turned off, even in darkness. Easy!! When testing the other extreme by completely cutting off the circuit the lights always were on.

• Short circuit the brightness sensor: Clock thinks it is daytime and LEDs are off
• Disconnect / cut off the brightness sensor: Clock thinks it is nighttime and LEDs are on

Now… although short circuiting works and no component got hot in my primitive testing it’s probably still better to use some kind of resistor if we a replacing the brightness sensor with our DIY always-off sensor. Since the brightness sensor also works as a type of resistor I tried out a couple of different resistors of different resistance values. Up to 1.0MΩ (= 1000kΩ) everything worked. I arbitrarily decided to use a 12KΩ resistor as that felt like a good compromise.

Simply cut off the connections between the cables to the brightness sensor. Then take your trusted soldering iron and connect the reconnect the cables using a resistor in between.

Replacing the sensor input with a transistor

That’s it! Put everything back together and you are done.

I have been living with my modded clock for a week now and it’s still ticking as before. No problems so far. I can’t make any statements on any battery draining problems but I doubt that this modification is critical in any way, shape or form. If you have more detailed information on the brightness sensor or resistor to use please share it in a comment.