After short circuiting a 12 Volt hair dryer which I used for dew prevention at a starparty a few months ago, I thought it was time to get a real dew controller and a dew heater for my scope.
An average dew controller costs more than 100 Euro (or US Dollars) which is, in my opinion, quite expensive for something that only controls voltage between 0 and 12 with a potentiometer.

One or two years ago, ‘rwagter’ a user on the Dutch Astroforum, came up with the idea of using a cheap 12 Volt LED dimmer as a dew controller.
After that I’ve seen numerous dew controllers using this LED dimmer created by people on the Dutch Astroforum and Stargazers Lounge.
I’m not a electronics buff at all, but after reading how people had built their own, I would give it a try.

The dimmer costs about 4 US Dollars each on eBay, and most of the time shipping is free.
After ordering, you’ll need to have some patience because delivery from Hong Kong can take 4 or more weeks.
Just search on eBay for 12 Volt LED dimmer and find the one that resembles the picture above because that’s the one you’ll need for this DIY project.

For my DIY project I’m using 2 dimmers and each dimmer outputs to 2 channels.
You can connect a dew heater on each channel, so in my case I can connect 4 dew heaters.

Components
2x 12 Volt LED dimmer
1x lighter plug for connecting to a powertank
4x RCA chassis mount (female)
2x 5mm red LED (diffuse)
2x LED holders (plastic)
2x 2200 Ohm resistors
1x casing to put it all in
some cable

Tools
Screwdrivers
A soldering iron
A drill to drill holes in the casing
Nice to have: a Multi meter

The LED’s and the resistors are not mandatory. I thought it would be fun to see the LED light dim when using the potentiometer 🙂

Total costs (including the 2 dimmers) was 30 Euro.
You can reduce the costs by using only 1 dimmer, a smaller case or just by re-using the dimmer case.
The case and the lighter plug (I bought a fused one) were the most expensive: both around 8 euro.

Building the dew controller is pretty straight forward.
The first 2 connectors on the dimmer are 12 volt input (V- and V+), connectors 3 and 4 are output (V+ and V-).
Power from your power supply goes into the input and the output connects to a RCA connector.
The only thing you need to keep track of, are the + and the – connections.

I’m using 2 channels per dimmer, so if you want to do that too, you’ll have to connect them in parallel.
That’s really it.

If you want to add some LED’s, take a look at this picture (courtesy of Gina/Stargazers Lounge):
The only thing what’s wrong in this picture, is that the input and output connections of the dimmer are switched.
Got me puzzled for a few seconds.

Here is the result of a Saturday afternoon drilling and burning my fingers by the soldering iron.

Now I’ll have to wait for clear skies and loads of dew 🙂