The Shop > Electronics & IC Programing

Encoder bulb replacement?

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I have a Heidenhain clone encoder that refuses to work. Can't be too difficult to fix, given how simple the electronics are and I don't imagine the mechanics are the root of the problem - it all looks and feels OK.

Sure enough, the mechanical bits comprise an optically slotted glass wheel with a similar slotted (stationary) grid providing a sort of Vernier effect. It's lit from below through a simple lenswith a 5V incandescent bulb the size of a matchstick head. Or was until the filament burnt out. There's also some sort of flat optical receiver for the A, B and Z outputs.

Beyond that, there's a quad comparator and a couple of RS422 differential line drivers. Looks to me as if replacing the light source would be all that's required.

Has anyone any experience of these things? I'm tempted to liberate an LED from a modern light bulb and use that with a suitable resistor, rather than try to source a miniature 5V bulb. Apart from anything else, the available space is an issue, which rather limits my options.

The things you are probably after are called 'grain of wheat bulbs'.  Wire ended mostly.
Used to be quite common, but not so much now but still obtainable.
Various voltages usually 3, 5, 6, 12V.  About 5 years ago I dumped about 200 of the things, 24 & 32V. Never found a use for the little buggers.  :scratch:
EDIT  New link ...

What size is the bulb? I'll look in my collection.of odds and sods.

You might get a led to work but you may need an infra red device and it will need to be trimmed (vary the series resistance) to get the right light level (which is usually quite low , i.e 6v bulb running at 5v.)

I will try to measure it although it's embedded within some sort of epoxy(?) adhesive. But 3mm is about right. If anyone has anything suitable, I'd be more than happy to reimburse and/or make a donation.

Must admit, I'm a little unsure about what wavelengths would work here although it's a normal looking bulb so you might guess visible light would work but can't rule out IR. The sensor has no markings, so I can't look it up.

The CPC bulbs are pretty cheap at 1.62 for 5 but as ever they want 4.99 for "handling". Speaking personally, I'd expect more than just a rough grope for a fiver but that's just me.

I may experiment with some LEDs in a bit and see if that might work.

Photo trannys are often/usually ir  , you won't get any ir out of a 'white, led (just a mix of red,green and blue)  but bulbs  give out more ir than visible when run  cool  for long life.

Ill go have a look in my bulb box....


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