It's been a while but I've managed to run a couple boards with the design. They are eagle format so feel free to take a look. based around an ATMEGA168, there is a thermocouple amp, accelerometer, and a couple buttons and LEDs. Quite a small system so it can fit into the barrel of the pen. The MOSFET should be okay running 24V with a good few amps but I haven't tested it yet. I've got it all running except the micro. Can't seem to get it programmed using an arduino set up as a programmer. As a side note, the three pole connector at one end of the board is for a headphone jack, specifically this one LUMBERG - KLB 4: http://uk.farnell.com/lumberg/klb-4/soc ... dp/1200144
It's mounted by just sliding the terminals between the PCB and they line up perfect, just needs to be the right way around.
I haven't worked on it in a wile due to exams and such but might get back to it at some point. I've recently bought a "hakko-like" soldering station and hot air gun so got less motivation to finish this. If anyone is interested in finishing it, feel free, just remember that the amplifier only gives good readings where there is no power to the tip, i.e. between pwm bursts.http://www.2shared.com/file/iMGlir1r/So ... onics.html