Polarscope LED Installation

Many Equatorial Mounts are supplied with Polarscopes (or the necessary tube in which to install one as an optional extra) but often these are not illuminated which means that it is necessary to shine a light down the polarscope tube to illuminate the calibration reticule. This is no easy task and involves contortions of the head and body that make polar alignment a real chore!

This simple project allows you to install Polarscope illumination inside your polarscope tube and to power it either from a 12v or 4.8v (nominally 5v) battery pack or Power Supply Module (PSU). The components required are readily available from Maplin.

If you already have a 12v supply available for powering your mount then you will require one of the 12v LEDs shown below but if you do not have a suitable 12v supply then it is probably easier to buy the 5v LED version shown below and make up a small pack of 4 X 1.2v Nickel Cadmium (NiCad) or NiMH (Nickel Metal Hydride) cells. I have chosen the special type of LEDs below for this project as they make life simpler as they come with an integrated current limiting resistor in the package.

LED Type Maplin Reference Comment
12v Standard 3mm Red LED CJ66W Standard brightness
12v High Brightness 3mm Red LED CJ70M Ultra brightness
5v Standard 3mm Red LED CJ64U Standard brightness

It will be necessary to solder wires of suitable length to the two leads exiting the LED package. The longer of the two leads is the 'Anode' and this should be connected to the positive (+ve) terminal of the battery/power supply and the other lead (Cathode) connected to the negative (-ve) terminal. I recommend that the soldered connections are protected with heat shrink tubing, also available from Maplin, to ensure no short circuits!

Once the soldering is completed, the leads may be bent at an angle in such a manner that the LED points straight down the polarscope tube towards the polarscope itself. The LED leads should then be glued into the mount housing such that the LED is suspended in the centre of the polarscope tube as shown below. I used 5 minute Epoxy to do this, having prepared the mounting surface in advance by cleaning it with Methylated Spirit to remove any traces of grease or dirt. I also secured the wires with tape within the housing so that pulling on them would not dislodge the LED

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