After the module died last weekend I tried to look into how I can solve the problem of needing a 500kΩ variable resistor that could take >30v on the resistive element. I found there was no such device, the largest available high voltage device is 100kΩ, so I'd need 5 of them in series, with the wiper resistance being 75Ω, that's a minimum resistance of 375Ω which may be too high. I then went about using a chain of resistors in series and a device to "short out" unwanted ones to get various values. A CMOS analog switch was out of the question due to that 30v requirement and a solution using MOSFETs is out of the question because of the variable Vgs will cause variable Rds, which will in turn cause varying amounts of "bypass" on the fixed resistors meaning that it will be nearly impossible to control.

So that idea was not going to work.

I then came to the realization that perhaps I was making this too difficult and I needed a completely different approach. Instead of trying to hack together a control mechanism for something that was not designed for this, I needed to take a step back and think differently.

I am going to implement the buck-boost section with discreet components and use the microcontroller to control it directly. I think this will actually prove to be an easier solution, and will definitely offer a better prospect of success.

However, as I will be ears deep in PCB design and waiting for parts, I may not have a whole bunch of updates in the blog