IR sensor
Posted: Sun Feb 26, 2017 7:24 pm
Time to revisit the IR sensor LEDs. THese always gave me trouble and I kept blowing them up. I wonder if it was my dodgy power system.
Anyway, I have a IR LED and corresponding receiver. First thing is to hook 'em up and see if they work.
These days it's pretty easy to test the emitter - just look at it with a smartphone camera...
And yep, works just fine. I put it on an old pencil, and used a hot glue gun to fix that pencil in place (temporarily) - way better than sticky tape I was using a decade ago. Looking again with my camera, I made sure that the LED was shining through the timing holes and I could see the 'purple' as each hole passed. With that done, I also glued down the receiver-side. This dual-pencil setup is just a temporary kludge. I'm pretty sure I'm going to be 3D-printing a mount for the IR sensors so that they are guaranteed to be facing each other, and the gap is a set distance. Should be easy - will get to that this week. But for now, pencils and glue.
Next I hooked up the 'scope to the leads of the receiving diode thing. I expected to see a voltage change as the holes passed. So I spun up the disk (it's not controlled speed yet, just runs on whatever the 12V makes it do) and had a look at the signal...
OK, that looks pretty good! I'm getting a low voltage when there's no hole, and a significant voltage when there is - about 2V difference. That should be good, I think. In the image above I've clearly caught the taped-up 32nd timing hole. Since the spikes are about 2.2ms apart, the disc spins once every 2.2*32 ms = 70.4 ms, so it's running at 1000/70.4*60 rpm = 852 rpm. Overspeed but that's exactly what I was seeing.
Next thing I think is to get the motor hooked up to the correct outputs from the control circuit and see what happens. I have to trace the correct location on the circuit board, because the wires had broken off and yeah... no documentation. Currently I'm just feeding 12V to the motor - good to know it's not way overspeed but certainly not underspeed at that voltage.
Anyway, I have a IR LED and corresponding receiver. First thing is to hook 'em up and see if they work.
These days it's pretty easy to test the emitter - just look at it with a smartphone camera...
And yep, works just fine. I put it on an old pencil, and used a hot glue gun to fix that pencil in place (temporarily) - way better than sticky tape I was using a decade ago. Looking again with my camera, I made sure that the LED was shining through the timing holes and I could see the 'purple' as each hole passed. With that done, I also glued down the receiver-side. This dual-pencil setup is just a temporary kludge. I'm pretty sure I'm going to be 3D-printing a mount for the IR sensors so that they are guaranteed to be facing each other, and the gap is a set distance. Should be easy - will get to that this week. But for now, pencils and glue.
Next I hooked up the 'scope to the leads of the receiving diode thing. I expected to see a voltage change as the holes passed. So I spun up the disk (it's not controlled speed yet, just runs on whatever the 12V makes it do) and had a look at the signal...
OK, that looks pretty good! I'm getting a low voltage when there's no hole, and a significant voltage when there is - about 2V difference. That should be good, I think. In the image above I've clearly caught the taped-up 32nd timing hole. Since the spikes are about 2.2ms apart, the disc spins once every 2.2*32 ms = 70.4 ms, so it's running at 1000/70.4*60 rpm = 852 rpm. Overspeed but that's exactly what I was seeing.
Next thing I think is to get the motor hooked up to the correct outputs from the control circuit and see what happens. I have to trace the correct location on the circuit board, because the wires had broken off and yeah... no documentation. Currently I'm just feeding 12V to the motor - good to know it's not way overspeed but certainly not underspeed at that voltage.