With the prospect of implementing a "2-switch" non-inverting buck boost DC-DC converter, I started to redesign the board, which involves choosing the n channel FETs, and a high/low side driver for them, the Schottky diodes and most importantly the energy storage elements (an inductor and a capacitor).

At the weekend I picked up the courage to plug the PWM filter connectors into the voltage control on the module, and it appeared to work, dialing the PWM output higher caused more voltage to come out, turning it down caused less. Yet there were problems...

After measuring the voltage on the divider, it seemed ok, as it varied linearly with the output voltage, it was also right around what I calculated it should be it's a 90k/10k divider so the output voltage of the divider should be (and is) very close to 10% of the post voltage. However the output of the opamp (configured as a unity buffer) does not go much above 1.9v which is why the ADC tops out at ~19v.

After the PIC24 redesign, it has been my wish to use the realtime clock so that the reports to the serial port can be made with the correct time. Unfortunately when the processor loses power, the clock stops and the time is reset.

To get around this, I figured that I would use a battery and the low power characteristics of the microcontroller. When I designed the board I added the battery holder for a CR2032 and an LTC4411 from Analog/Linear to manage the switching between the power sources.

I went through the process of writing the heap_malloc function, and got it ready for the initial testing. I decided that I would do that in the simulator, so I added a heap_malloc of 1 byte to the main function. On the first run, the code crashed with an invalid program counter. This is the block of code with the crash