I know this is probably something simple, but anyway…
I have an LED 12v strip, nothing fancy, single colour, 1 anode, 1 cathode, resistors built in, which I’d like to control using the spark core. I’ve tested this on an Arduino and it’s fine, works as expected. I can analogWrite various values to control the brightness of the strip via an NPN MOSFET . I’ve used this approach several times before, with 5v as the control voltage and always without problems.
However when I connect my NPN and LED strip to the core, I only get about 7.7volt reading across the strip when I digitalWrite HIGH to the control pin, which causes the strip to be very dim.
The thing is, I can’t figure out how the NPN knows that I’m using 3.3v or 5v. The 5V is a separate power source which goes straight into the core (and is subsequently regulated down to 3.3v internally). I know the pin is only supplying 3.3v, but how does the NPN transistor know that it should expect 5v to turn on the controlled circuit 100%? Why won’t it accept 3.3 and give me full brightness of my LED strip?
I’m essentially using a simplified version of this circuit, with a single LED circuit (rather than 3), and no voltage regulator (i’m using a PSU from an external hard drive, which supplies 12v and 5v rails.)
Is there a resistor or something I should be using to get this working?
ps: not sure what category this should be under, it’s not a specific core issue, so I didn’t want to put it in hardware or troubleshooting.