Categorie: DIY

Making a cheap dew controller using a LED dimmer

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.

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

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

dewc_componentsThe 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):
ledsThe 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 🙂

Remote control your GoTo telescope mount using a Raspberry Pi and SkySafari

SkySafari is a great astronomy app for smart devices like the iPhone, iPad and Android.
The SkySafari Plus and Pro versions add the possibility to remote control your GoTo telescope mount using the special SkyFi adapter.
This adapter sends serial (RS-232) commands, received with a wireless connection, to the handset of the GoTo mount.
Using SkySafari in combination with SkyFi increases the number of objects you can observe and current events in the sky (like comet PANSTARRS at the moment) are found easily this way.

I was wondering if it would be possible to create something like SkyFi using the Raspberry Pi.
And yes, it is possible. Quite easy actually!

What do you need?

  • Raspberry Pi configured with a working network connection (wifi preferred, of course).
  • USB to Serial cable.
  • GoTo telescope mount
  • PC Serial to GoTo handset cable. Shipped with your GoTo mount.
  • SkySafari Plus or Pro
  • Basic Linux knowledge

Now how are we to receive the commands from SkySafari?
This is done by the Serial To Network Proxy (ser2net).

Install ser2net:

sudo apt-get install ser2net

Add the following line, using your favorite text editor, at the end of the ser2net configuration file (/etc/ser2net.conf) which contains the port where ser2net is listening on:

4000:raw:0:/dev/ttyUSB0:9600 NONE 1STOPBIT 8DATABITS

In this case, I chose port 4000. You may choose another port but be sure it is between 1024 and 65535 and does not conflict with any other daemons listening on the same port.

Restart the ser2net service with the new configuration:

sudo /etc/init.d/ser2net restart

Next, configure your telescope in SkySafari.
My setup has a SkyWatcher SynScan GoTo on a EQ3-2 equatorial mount.
Be sure to enter your setup and don’t copy my settings bluntly 😉


The IP address in the picture above corresponds with my Raspberry Pi. Of course, you should enter the IP address of your Raspberry Pi.
Same goes for the listening port. I’m using port 4000.
If you configured a different one for ser2net, enter that one.

After that is done, you should try to connect SkySafari with your mount in the Scope menu and you’re off to go!