This is a completed project, expect no more updates or changes.

I'm still working on improving the Haber process, but using a different method, and I have made some progress. I'll start and update a new project describing my work at some point.

People have been asking about transducer power supplies, so here is a list of "Lessons Learned" that might be of interest to others.

LESSONS LEARNED

Firstly, make a circuit that's self-resonant. Trying to keep the transducer in resonance across changing conditions is a PITA, and the conditions will change based on the transducer heating up, changes in the moisture content of the air, and myriad other factors that cannot be easily controlled.

Instead, make an oscillator with the transducer as the oscillating element, or make some analog feedback that automatically constrains an oscillator to the transducer frequency. The Cheap Chinese circuit described in my log entry (link below) shows one way to do this: take the return from the transducer through a toroid, and then wind a secondary coil on the toroid to tap off a synchronous signal, then use that signal to run a push-pull circuit of some kind.

https://cdn.hackaday.io/images/7856741430093121127.png

(An induction heater circuit seems like a good way to drive the transducer. You would still need feedback to get the self-resonance.)

https://www.instructables.com/topics/HELP-measure-resonate-on-induction-heating-/

Next, don't use an Arduino for [direct] frequency measurements or generation.

The Arduino timer resolution at the transducer frequency doesn't have sufficient resolution. You could a really high frequency micro such as a RasPi (1.1 GHz) or an SDR digitizer or similar.

A much better way to do this (than using a micro) is to get an AD9850 board from eBay and command it using an Arduino.

Next, don't use a cheap transducer from eBay.

It turns out that the transducers available on eBay are rejects - they're slightly off frequency and have a very low "q-factor". This means that they are "mushy" and don't ring very well. It's like the difference between a metal bell and a plastic bell - because the plastic has a low "Q", it doesn't ring very loud.

Instead, bite the bullet and get a quality transducer from a known source, which will ship with specs from testing.