It's been a while since I updated this... The main reason being that the control system was good enough to be used for actual experiments, so I had to work on that rather than finishing improving the hardware and software.
I have made some progress though. On the software side, I've added bluetooth support and implemented a basic-but-usable front end for routines. I'll update about those things soon.
On the hardware side, I've had some issues with the pressure regulators I bought. The main issue is that they leak a lot of air through an internal vent.
The vent is there by design -- according to the manufacturer, it is necessary for an application that consumes little to no air -- but unfortunately it vents way too much air to make it possible to use the on-board pump at any reasonably high pressure. And when I use a compressed nitrogen tank, I go through an entire tank in ~4-5 hours of use.
I think this is quite silly, as I'm working with nanolitre volumes but require massive tanks of gas to do so.
This on its own would be enough to warrant a better solution, but there were also other annoying issues:
- When the actual pressure dropped below the setpoint, the regulator would output a value somewhere between the setpoint and 25% of the maximum value, instead of the actual measured pressure. I.e. if the supply suddenly died or started leaking, you might have no idea.
- Control is between 10% and 100% of full scale, which is not ideal for my particular application where I'd like precise low pressure regulation.
The manufacturer wasn't particularly helpful with support, and wouldn't exchange the regulators I had for more suitable versions, so I thought I'd make my own instead. How hard could it be?
Anyway, I started a separate project page for my DIY pressure regulators. All the details are there: https://hackaday.io/project/148274-electronic-pressure-regulator . I'd love to hear any feedback on that project!