Dim Everything Make the lights in the boat dimmable

ZwerfCat came with filament type lights but we replaced them with LED lights everywhere. Some of these LED's turned out to be really bright, sometimes this is handy, but more often we like a more "cozy" illumination. I couldn't really find light dimmer conversion kits for boats, so I decided to design my own.

Some people who noticed our dimmers expressed their desire to have them too. I have ordered a small batch of readily assembled units and I will also make the design available for those who are willing and capable to build it themselves.

How to use

A short press on the button will switch the light on, another short press will turn it off again. Easy peasy. The last used dim-setting is remembered.

When the light is on, you can change the dim-position by pressing and holding the push button. The light will slowly go from its current position to the brightest position, then slowly revert to the most dimmed position, then climb up again to the brightest position, etc. Just release the button when it is at the desired dim position. If you press the button and it is going "into the wrong direction" you don't have to wait for the cycle to complete, just release the button momentarily and hold it again, the direction will now be the opposite.

Guests on our boat finds the dimmers easy and intuitive to use without any explanation required.

Soft-start & fade out

If the light is switched on, it doesn't immediately go to the last remembered dim-position but "soft starts". When you switch off the light, it will "fade out". This behavior just gives a nice luxury touch to the illumination.


On boats it is often handy (like during a nightly passage) if the lights don't go on at their last used dim-position but instead start at the most dimmed position. To do this, use a "long press" instead of a "short press" to switch the light on.

While the light is on there is a shortcut to go directly to the brightest or dimmest position by "double clicking" the button. With each "double click" it will go to one of the extreme positions. Handy if you suddenly need maximum light!

The design

LED lights are technically easy to dim, especially for the low voltages used on boats, but you need some electronic parts and a micro-processor to control everything. The design-goal was to make the dimmer compatible with the existing wiring and LED bulbs, and intuitive to use.

We have LED bulbs from different manufacturers and almost all of them are dimmable.

The mini-version

The mini-version is really mini and is intended to be fitted inside an armature, but of course you can use it anyway you want. The mini-version can only be used with the output in the minus (usually black wire). This is easy to do inside an armature, but with existing wiring inside a boat usually the plus (usually red wire) is only available in the standard switch housing. Also, this version has no switch or LED on its own.

If you want to use it inside an armature, you will have to replace its switch by a momentary push button.

The generic version

This version is bigger but can be used with the output in the minus as well as in the plus. Also, it has an LED and push button builtin. In addition, it has an input for a light sensor, so the light can go on automatically. You can for instance use it to automatically control your anchor light.

There are two ways to install this dimmer:

  • The easiest way is to mount it somewhere where you can access the builtin push button. It can be mounted ON a wall, but you can also separate the front panel and built it in flush with the wall.
  • You can also connect an external switch to the dimmer so you can mount the dimmer somewhere out of sight. If you want to maintain the style of the wall switches which are already on your boat, you have to replace the switch by a momentary switch which only "holds" while you keep pressing it. Surprisingly, the switches that were already on ZwerfCat are also available in momentary switches, with the same dimensions and style. Probably the same kind of switches are used on many boats. I might be able to help locate your type of switches in you send me a picture and the dimensions.

Overview of both versions

Mini versionGeneric version
HousingShrink tubePlexiglass housing with detachable front panel
Mounting optionsConcealedConcealed, on the wall, flush mounted
OutputNegative onlyNegative and Positive
Builtin Push ButtonNoYes
Builtin LEDNoYes
Sensor inputNoYes

Technical details

The dimmers are compatible with 12V and 24V board nets. The dimmers use Pulse Width Modulation at a frequency of about 400Hz to "dim" the illumination, which is too fast for the human eye to see any "flickering". Maximum current is about 3Amps (no hard limit) which should be enough for at least 12 parallel normal LED lights.

How to build it yourself

A small programmable microprocessor (ATtiny85) is used for this project, which needs to be programmed. You need to have a compiler (Arduino-IDE works fine) and a suitable programmer.

The build it yourself project (schematic diagram and software) will shortly be presented on GitHub.


We are ordering a few ready to use Dimmers and they should become available soon.
Price of the mini is expected to be around 25 Euro's.
Price of the generic version is expected to be around 45 Euro's.

We don't know how fast they will go, if you want to reserve one or more units, just let us know.


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