Adding Status LEDs to input & output lines.... between microtroller & device

[difr]

Adding Status LEDs to input & output lines.... between I/O Controller & Robot

Hi

I have an existing I/O controller connected to a robot arm. I'm wondering, how can I add some status LEDs that tap into the input & output lines so I can make a little LED display for troubleshooting etc.

Please see my rough schematic: (only shows one switch/motor for simplicity)



I thought I might need to use a buffer (like 7407) to isolate the LEDs, but maybe a transistor will do. Also, it's not really practical to cut into the existing input/output lines - I just want to tap off them. Also, the output lines are 24VDC 3A, so I don't want to cut into those.

So if I want to test that the input switch is working, I can manually push it and the status LED will light. It would also light during normal operation of the robot.

And a different LED would light to indicate that the motor should be running, or even an LED for each direction (forward/reverse).


Thanks for your help,

Dan.

 

[dr pepper]

Re: Adding Status LEDs to input & output lines.... between microtroller & device

Your drawing is rather basic, the micro obviously will not control the 24v directly, there must be a transistor or transistor/relay controlling the load.
You can so long as the micro has enough current output, and most do, connect an led direct to the pin of the micro, if it runs off 5v then you need a 470r resistor to ground.
If the micro only has limited current outputs then you need a transistor, a bc547 will do, connect the base to the micro output via a 10k resistor, connect the collector to +5v, and connect the emitter to your led via a 470r resistor and then connect the led to ground.

 

[difr]

Re: Adding Status LEDs to input & output lines.... between microtroller & device

Hi Dr P, sorry if the word microcontroller in the subject caused confusion. So the I/O controller is driving 6 motors directly, it's got onboard H-bridges and the outputs lines are 24v 3A, and I deliberately made the blocks at each end simple so as to emphasise that I just want to tap-off the I/O lines.

I'm sure the controller could easily drive an LED as well as a 3A motor but I thought using a buffer was the right way to do it - whenever I've seen schematics for I/O controllers that DID have status LEDs, I remembering seeing buffer chips. But searching around, the only schematics I can find that have status LEDs, they're wired in with the output driver transistor or optocoupler, and I can't really go tapping into that.

 

[luben111]

Re: Adding Status LEDs to input & output lines.... between microtroller & device

Hi
One simple schematic is the attached one. In case the voltage on motors is less than 5-6 V you can remove the diodes which protect the LED against opposite voltage. If using 2 color LED you can simplify it even further - no protective diodes are needed