I am working with an FTC team and need an example circuit that I can help them get wired up to drive a string of LEDs. We can’t directly connect the power so we need an optoisolator.
I am not an expert, but the optoisolators I have found can drive 10’s of milliamps and the strings of LEDs I have are in the 200mA range. So I assume I’ll need the optoisolator to drive a MOSFET which will controll the LEDs.
What I could really use are some example part numbers that we can order and get quickly. I know just enough to be dangerous <grin> so when I think I’ve found a part that might work well then I find I can’t get it for 3 weeks. <sigh>
Thanks for any pointers to circuit diagrams and/or part numbers
It seems like they suggested this as a possible option in their response.
I’m not familiar with the FTC rules myself, so I can’t comment to its legality.
Relays can be sourced locally at radio shack. You probably only need a SPST relay.
It looks like the HT SuperPro has 3.3v outputs, so you wont be able to drive the relay directly. Luckily there’s lots of circuits online on how to control a relay from a microcontroller. Like this. One modification to the circuit on that page though - I would suggest adding a diode across the relay coil as shown here.
Common diodes 1N4004, 1N4001
Common NPN transistor 2N3904 This relay should work if you’re switching 5volts to the LEDs. This one if you’re switching 9volts to the LEDs.
The rules on FTC are much more limiting. We have to use a prototype board for things that aren’t part of the standard control system. And that board has limited power it can source.
I don’t think a relay will work, because I have only about 12mA @ 12V (or 20mA @ 5V) that I can use to drive the coil. I can get some mini relays that are in that range, but then I can drive only 1 at a time and we would like to do several.
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