Had our usual weekend tinkering this Saturday.
Breaking News: We got our own Slurpee machine! Some highlights:I came across the Super Probe two weeks ago, and just had to make one. I had a bunch of the PIC 16F870 microcontrollers left over from an earlier project, and the rest of the parts were all easily found in my parts collection.
Over the last couple of months, Gav and R3becca have been discussing a new project idea - the Geigerduino. The idea being to be able to build an simple device that can detect cosmic rays or other radiation using a Geiger-Müller tube and an Arduino, and then publish the details so others could do the same. In late August, whilst having an R&D group dinner at Rockdale McDonalds, Gav quizzed me about generating high voltages, and I drew a rough schematic of a DC/DC boost converter (on a napkin of course). He told me the goal was to generate a PWM controlled voltage of up to 1000 V, using USB as a power supply. Having planted the seed, over the next two weeks I did some additional research and realised we should try a DC/DC converter using an isolated transformer with a voltage multiplier to get this kind of output. So, two weeks ago, we began prototyping this at the space. I built up a simple circuit on a breadboard, using a small transformer, some high voltage diodes and capacitors, and a MCP14E5 mosfet H-bridge driver chip. I had acquired a small batch of these transformers from a surplus electronics place a few years ago, and they seemed appropriate with a DC resistance of 11.5 ohms on the primary, and 2,300 ohms on the secondary. I had no other specs, but I think they were intended for generating HV to drive EL or CCFL lighting. The MCP14E5 is actually intended to drive the gate of power MOSFETs, but I had it handy, it is fast and can supply significant current, and it seems to do the job. I also needed a signal source to drive the transformer, and seeing as R&D had recently done a group purchase of Bus Pirates (preorder 2), I decided to use one of those. The Bus Pirate has a PWM generator mode that can generate 1 kHz to 4000 kHz signals with varying duty cycles.
