µMute – A microwave oven silencer

I’m tired of the buzzer in the microwave oven that is beeping constant up to a minute.

So I opened it up like any normal hacker would, found the buzzer and snapped it off.

Sure, the buzzer was irritating, but so would be not to hear when my food is cooked. So i quickly had a look at the PCB and find a very interesting pinout.

So I soldered on some pins and started to measure the voltage level.
VCC of 5V looked promising for a microcontroller.

I had a look at the buzzer signal, it was a 2kHz signal with an amplitude of 5VDC.

I had a rough idea in mind about having a small tune play instead of the 2kHz tone, and it should only play once.
So I shuffled some code together to code to play a small tune from the flash of an Arduino Nano. The flash could only hold about 18k of samples and was played at 8kHz.
(inspired by http://playground.arduino.cc/Code/PCMAudio)
In lack of a better choice i choose Windows XP’s startup sound.
I shuffled some more code around to sample the original buzzer signal from a GPIO. If the sound is playing at more than 2kHz for a certain time I would trigger the sound.
I applied some time based software filters to filter out some noice.
I build a small amplifier out of an MOSFET (IRLML6344) and a small 0.5W speaker element I found at my local hackerspace.

I throw it all into the chassis of the microwave oven. There was plenty of space, but i took some precautions to electrically isolate the PCB and speaker.

Unfortunately the sound from the small 0.5W element was too low. It barely was distinguishable against the sound of the microwave ovens fan.

So I upgraded the element for a 3W element that I found in an old PC speaker, and took some precautions and upgraded my amplifier as well for the more stable Class-D amplifier PAM8403.

Schematic PDF

The sound was much louder and you can clearly hear the “Done”-sound from the microwave oven.

Festivalljus – LED, Lens, Heatsink Assembly

Assembly Spotlight With Chassi 3D 1
One of the hardest things with this project is to solve the problem with the heating. 9 pieces of 3W LED tends to get very hot, 27W that have to be transferred to the air.

LED 3DLED Inverted 3D
If I bend the pins on the led I can make the LED’s go through the PCB. An alternative is to use a lot of small via’s under the LED to transfer the heat to the underside. But I think a direct contact with the heatsink will be more effective.

Assembly PCB with LEDs 3D Without Lens
Assembly PCB with LEDs BottomAssembly PCB with LEDs 3DAssembly PCB with LEDs SideAssembly PCB with LEDs Top

Assembly PCB with LEDs 3D With Heatsink Fan
Assembly PCB with LEDs 3D With Heatsink LensesAssembly PCB with LEDs 3D With Heatsink Side
A CPU cooler should be sufficient enough to transfer the heat out to the air. I don’t know if the fan is necessary.

The whole assembly will look something like this:
Assembly Spotlight With Chassi 3D 2Assembly Spotlight With Chassi 3D 3Assembly Spotlight With Chassi 3D 4

Optics Specification

Interactive LED balancing board

A video posted by Tim Gremalm (@timgremalm) on

An interactive game were the visitors can build complex structure with help from an interactive LED balancer.
The installation was part at Vetenskapsfestivalen.

It’s a project by Stig Anton Nielsen read more about it in this post.

TeiSteadyBuilds from stig anton nielsen on Vimeo.


A video posted by Tim Gremalm (@timgremalm) on


The loadcells is build from 16 layers of conductive carbon packaging film. The recistance ranging from 500k to about 450 Ohm loaded at 8kg. Because it’s a so huge range the loadcells can be directly hooked up in a voltage divider, no amplifiers needed.
3 load cells us used to detect the direction and force of the balance. They are really sensitive to touch, small pressures from fingertips will be easily detected. A backside is that the film tends to be squashed so that it takes long time form the form and resistance to return.
The value from the 3 loadcells is arranged in 3 forces 120 degrees apart. The Forces is calculated into a resultant that is describing a thrust vector.
The thrust vector is indicated with a led strip of addressable WS2812 LED light. The stronger the force, more inbalanced, the greater the red marking will grow.

Att this Google Drive document I’ve collected som measuring data from the loadcells. There’s also some information of how the resultant is calculated.

Positional LED lights for Electric Longboard

I made some positional lights for my electric longboard to be able to be seen in traffic.

The rear red light have to be able to fold in when the board is placed on its butt.
A hinge was mounted, and a spring is holding the light tube up.

White electric tubing is used to protect a LED-stripe from dirt, it also diffuses the light.

The LED-stripes is powered by a buck converter, switching the voltage down from 25V to 12V.



Battery Chassis for Electronic Longboard

To have the LiPo battery’s exposed underneath the longboard could damage them if something hit them. A strong chassis for the battery’s would protect them, as well as covering the cables from dirt.
The chassis is primary made out of 8mm polycarbonate, with a sheet of 1mm flexible PET cover.
The 8mm thick sides will hopefully take up the forces from any direct bumps.

CAD Drawings

CAD-files (Zipped Solidworks and DXF)

Cam Lock Screw

For locking the chassis to the board I used cam lock screws, the same that is often used in IKEA furniture.
The cam lock seems to come loose due to vibrations, so another solution might be needed.

CyckelLjudet & Festmaskinen at Regnbågsparaden West pride Göteborg

After assembling CyckelLjudet we managed to arrive at Götaplatsen were the parade Regnbågsparaden were supposed to start.

The solar panels worked really great, we had no trouble at all and the LiPo was charged nicely.

We did use an old Sennheiser wireless transmitter to send the audio from the DJ-booth at Festmaskinen to the PA-speakers at CyckelLjudet.
We had some problems with wireless interference, but it hold up well most of the parade. Go 80’s technology!
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CyckelLjudet – Attaching electronics and solar panels

All pimped out and ready for the west pride parade Regnbågsparaden!

IMG_0010 IMG_0009
To be able to drive the amplifier for the speaker we use an UPS. On top of the UPS you can see the solar regulator Solar80.
The solar regulator is charging a 6S 8Ah LiPo battery pack. The solar panels will generate maximum of 600W of power, and the PA-system will draw about 65W of power, so the battery will be more of a buffer.

After some spec-readings we realized that the Solar80 wouldn’t handle the maximum of 70V that the solar panels could generate, it only supported 48V. So we switched it out for Flexmax 80.
Both the controllers were designed for lead-acid battery’s and not for LiPo battery’s. I was missing a parameter to set the charge voltage, also there was software limitations that you couldn’t go around, like the charging current for example, you could only go as low as 5A.
We’re trying out the solar panels and solar regulator in the sun charging the LiPo. The stop-charing-limit was set to 25.2V which is the voltage of a maximum charged LiPo, but the solar regulator was still inputing voltage well above 25.2V because the solar regulator is designed for lead acid battery’s. We then set the maximum-charging-voltage to 24.8V that seemed to help, the voltage over the battery didn’t reached over 25.2V.

Cables from the solar panels.

IMG_0007 IMG_0006
Amplifier/mixer in place, and so is the LED-bars.

IMG_0005 IMG_0004 IMG_0003 IMG_0002 IMG_0001 IMG_5570 IMG_5568 IMG_5565 IMG_5563