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Noob question about resistors for LEDs, but for opto-isolator.

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BadMouth:

--- Quote from: DaOld Man on August 17, 2013, 11:53:19 pm ---So you are wanting to switch the resistance to the joystick LEDS, based on an output on or off from the PC?

--- End quote ---

Yup.


--- Quote from: DaOld Man on August 17, 2013, 11:53:19 pm ---How are you switching the opto isolators?
--- End quote ---

Eventually plan to use a usb Pololu servo controller.  It has a mode that can turn LEDs on and off instead of controlling a servo.
So far, I'm just using a test bench power supply set to 5v.

I might fry a few parts, but I'll get it working soon.
It was working for a fairly long time on the breadboard with the 100ohm resistor.
It never worked on my proto-board.  Maybe it wasn't the low resistance that killed the opto-isolator, but it's not good to exceed specs anyway.  I'll go back to the breadboard today and try to find a solution that uses the proper value resistor.

BadMouth:
circuit seems to work fine with a 220 Ohm resistor.   ::)
Hopefully I'll get the same results on the next proto-board.

As an aside, I left an opto-isolator on with a 100ohm resistor for a half hour and it didn't burn up.
I suspect i fried the one on the original protoboard with the soldering iron or poor routing.

DaOld Man:

--- Quote from: BadMouth on August 18, 2013, 01:22:45 pm ---I suspect i fried the one on the original protoboard with the soldering iron or poor routing.

--- End quote ---

This could well be, but hey, it happens to the best of us, so don't give up.

BadMouth:

--- Quote from: DaOld Man on August 23, 2013, 05:29:38 pm ---
--- Quote from: BadMouth on August 18, 2013, 01:22:45 pm ---I suspect i fried the one on the original protoboard with the soldering iron or poor routing.

--- End quote ---

This could well be, but hey, it happens to the best of us, so don't give up.

--- End quote ---

Pretty sure that's what happened.  I barely tacked the next one in and it worked fine.
The P1 side of my protoboard worked perfectly, but P2 refused to work no matter what I did.
The only difference was that the collector/emitter side of the opto-isolator is reversed.
I did that to make power routing to the anodes simpler.  I didn't think it made a difference, but apparently it does. 
Either that or there is some other problem I'm not seeing. 
I'll reverse them on the breadboard test setup and see if it stops working.  Otherwise I haven't really learned anything.  ;)

At any rate, my protoboard looks like crap from swapping parts, so I'm going to redo one from scratch that I'm not embarrassed to post pictures of.  :P
I'll use sockets for the opto-isolators and make two identical circuits.
Hopefully I'll get it done tonight and will post the final product on my Neo Geo Evolution build thread.

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