Last updated: 3 July 1999

Drive ON LED mod

From: Jeremy P. Carlo (jpc4256@megahertz.njit.edu)

Here's a modification I performed on my ETX, and thought it might be interesting to share.

One annoying thing about the ETX (don't get me wrong, it's a GREAT little scope) is that there is no indicator light to say whether the drive is on or off. Of course, th first night I took the ETX out I left the drive on, and the scope spun around all the next day and when I went to use it a few days later the batteries were dead. So I decided to install a LED indicator.

I thought about drilling a hole, but didn't want to do anything destructive. So...

You see those holes on the bottom plate? They're supposed to hold the three tripod legs, but I don't use them, nor as I understand do most people. And I thought that this would be a good place to stick a small LED, the kind that you can pick up for about 25 cents. Here is what I did: (it will certainly help to have a multimeter available)

-Remove the bottom plate by unscrewing the three screws holding it on.
-Locate the drive on/off switch, and remove the batteries.
-Next, use a multimeter to find two leads (i believe there are three) where the resistance is zero when the switch is "ON" and infinie when the switch is "OFF."
-Solder (or use clips - it will be easier to untraceably remove them should you ever have to return the scope :) a wire to each of these leads.
-To these wires attach in series a resistor and the aforementioned LED.
-Install the batteries
-Experiment with LEDs and resistor sizes until you find a combination hat does the following:
-Red LED (so you don't destroy night vision)
-LED fits snugly in the hole in the bottom (you will use tape or something to hold it in place, but it helps if it's a fairly good fit to begin with
-LED is the right brightness (if it's too bright it destroys night vision and wastes the batteries, too dim you can't see it) It may help to have a breadboard to test the components.
-Once you have selected the components, you are ready to reassemble the scope. Figure out a way to hold the LED in place while you place the bottom plat back on (I used electrical tape, and taped it to one of the support rods that anchor the screws for the bottom plate).
-Reattach the cover; the LED should be inside the hole, with its top flush with the bottom of the base plate
-You may wish to put some clear tape over the hole to hold the LED in place, and diffuse the light a bit.

It draws more power from the batteries, of course, but the power (and drive life) saved by not running the thing in its case for two days on end more than compensates for it.

Regards, and Happy ETX-ing,
Jeremy P. Carlo

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