This simple dew heater controller is a pulse width modulated circuit that runs off a 12V battery. It delivers a duty cycle between 5% and 78%, but this could be changed by tinkering with the circuit values. Almost any power MOSFET could be used here. With my 5.25 ohm dew heater the MOSFET runs completely cold so there is no need for a heatsink. The circuit includes some snubber components (C1 & R3) round the MOSFET which prevent the emission of any undesirable interference.
Dew Heater Circuit Diagram Picture of prototype
This little box connects to the ST4 guide port of most telescope mounts and makes the mount look like an LX200 for the purposes of autoguiding. The other end connects to a USB socket on your computer and appears as a Windows COM port there. It needs no power supply. It includes four directional pushbuttons so it can be used in place of a manual handcontroller. It has been tested with 'Guidedog', 'K3CCD Tools', and 'AstroArt'. It also obeys a subset of the ASCOM protocol.
USB Guider Circuit Diagram Assembly language program
Circuit of Toucam 740 Webcam Long Exposure Mod with amplifier standby facility:
Circuit of a simple opto-isolator box for connecting SBIG ST series cameras to a mount with a standard ST4 input. It includes red LEDs which illuminate when each direction is active, to assist in testing or fault finding. There is also a green LED to show when the unit is connected to a camera. Note that any optoisolator could be used provided that it has a current transfer ratio of about 1.0 or more. Also you could use two double packs or one quad pack for convenience:
Circuit diagram of the Losmandy Gemini Hand Controller: