The Shop > Electronics & IC Programing

Encoder bulb replacement?

<< < (2/2)

BillTodd:
These are the smallest I can find  they're 3 diameter by 6mm long , they  seem to have  a range of brightnesses at 5v  (some may be 12v)

let me know if they'll fit and let me have your address by pm.

Bill

Muzzerboy:
Thanks for the offer, Bill. I measured the bulb diameter and it was indeed 3mm, which suggests it was a common size. However, the thought of having to wait around for progress didn't sit well, so I had a go at fixing it. Either way I'd have had to clean out the old adhesive, bulb etc.

I found some of those tape LEDs. The package included a 12V battery with a switch and a single segment (3 LEDS per segment) wired up for sales purposes. This showed me that the forward voltage is about 3V under the recommended(?) current. I also measured 2.5V across the 150 Ohm resistor, suggesting a current of 17mA or so. Given that I have around 5V in the encoder supply, simply reusing this 150 Ohm with a single LED would result in around 13mA or so, a cunning plan came to be.

I snipped out one of the LEDs that was neighbouring the resistor and cut back the flex PCB to fit in the cavity where the bulb had been. I also cut and filed the cavity to get the LED roughly where the filament had been, then glued it in place with Araldite Rapid. With a layer of Krapton tape underneath for electrical isolation, it fits back into the original location. This was a bit of an act of faith, as it was only when I powered it up that I could be certain it actually worked. Which it did.

Obvs I couldn't move on without fiddling with the 3 pots. only one channel worked, so I assume the circuit is sensitive to the brightness to some degree. There's one per channel and there seems to be a sweet zone where the comparators do their thing. With all 3 in the middle of their zones,  I seem to have a result.

Pleased with this, as the same encoders are used on the 3 axes of my main CNC machine. This one came with in the bag of spares and claimed (correctly) to be faulty. It's now going to serve as the spindle encoder on my Bantam CNC conversion.

Many thanks for the offers of help and suggestions. Hope this helps anyone else encountering this issue.

Navigation

[0] Message Index

[*] Previous page