Hey Theo,
Have you considered building a local unit for Australia?
Or just one for me.
I should really learn to solder, after all I spent 5 years trying. I recall my Signals and systems professor kept telling us how every year we are at uni we are loosing 30K of income. So if you dont want to be here dont. He was a nice guy, old school.
I like the simplicity of PicAXE version, compared to that the no2 circuit is quiet complex. My head hurts looking at all those op amps. As it used to hurt in electronics lectures. No idea how I passed that one. However uP's and coding are more my cup of tea.
But build wise the no2 looks easier to do for starters.
Theo can you draw me a picture of your design.
Regards
Fahim