Nuts and Volts - September 2013

bandpass with a gain of one to remove any noise that might be picked up by the probe. IC2 also has a gain of 100 for a total of 10,000; the signal is inverted to reduce the chance of oscillation, but even so, careful layout and shielding will be necessary.

The final stage is a full wave rectifier and filter to give a DC output proportional to the sheet resistance. The LMV751 has a max supply voltage rating of 5V. I want to continue with plus and minus supplies, so I reduced the supply to ±2V using green LEDs.

I have been thinking about the static field meter and can’t find anything online about how it works. Early experiments measured the force exerted by charged objects, but I don’t see that as a way to measure the field in practice. It is not possible to take power out of a static field (or it will not be static), so I don’t know how to do it. Field-effect transistors operate on voltage, but 10,000 volts would zap it instantly.

Perhaps a voltage divider using capacitors would work but charging a capacitor requires current, and the leakage current of the transistor would charge the capacitor. So, that won’t work. Two foils will separate when charged due to electric repulsion, but I don’t know how to implement that. Does anyone have any ideas?

More About Making Sparks

QI’m back and I have better news, I think. First, I would like to say thank you. I have njoyed reading about my project in your June and July 2013 columns.