Well as promised, I got up early to head to the lab to test out the circuit and the news is…. we have success!
…well sort of. Of course there was some problems. So the first thing was I made a dumb mistake in the code, the pwm write takes a float between 0.0f and 1.0f instead of a int so the first thing was the output from the MCU was always high.
Fixed that, ran the code and got a nice square wave, nice! So I tested the critical points shown in the diagram (see below) and double checked my voltages though something was off instead of a nice square wave out of the scope I saw a sine wave with a random harmonic spike with a measured voltage between 50V & 80V. Of course there is no way that was the case double and triple checked the scope settings to no avail. Checked the wiring, everything still looked good.
It turned out I had the scope probe attached to the wrong ground. The since the MBED is connected to the PC for power, it’s ground wasn’t the board ground, so that was a dumb mistake.
With that sorted out, I could see the MOSFET was working fine, I connected it to the MOSFET gate and and tested the drain and yes I was seeing my 0-12V square wave, success!
So connected up the LED strip and expected pretty LEDs but again, nothing. Since I knew all my signals were propagating correctly I knew it was something with the LEDs and what I discovered is of course I had the wrong LED strip. I wanted common anode, I ordered common cathode (by accident) and I somehow got a common anode strip anyway. So that’s fine, I’ll switch out the mosfets and we’ll see some pretty lights soon. Expect another update, maybe tomorrow.