currentcurrent measurementdc/dc converterdetection
I try to detect a flow of positive charged ions. These ions produce an electrical current in the order of 10^-12 Ampers. My question is that, what is the simplest set up for detecting these ions?
Charged particles traveling in vacuum and hitting a metal box, When an ion hits the metal box, its charge is neutralized by an electron jumping from the metal on to the ion . That leaves a space amongst the electrons in the metal, and the electrons in the wire shuffle along to fill it.
If you don't have very strict requirements for how fast the cut-off is or how sharp it needs to be, polyfuses can be a great way to go. I put them on all of my designs.
They start to shut off when the current going through them gets too high. How fast they shut off depends on how much overcurrent they are. Once they're off, they stay shut off until you power-cycle the board. They're not great for enforcing a precise current limit, but they're perfect for preventing catastrophic failures.
Here's a sample:
http://www.digikey.com/product-detail/en/MINISMDC050F-2/MINISMDC050FCT-ND/1045862
In quantity 1, it costs $0.35. In quantity 1,000, it's around $0.17. It'll (barely) pass 500mA through it (250-300mA will get through fine), and will shut off pretty hard at 1A. It's dead-simple to use - just put it in-line with your source and you're good to go.
To convert 11.1 V to 9V you can simply use the 7809 regulator IC.
Best Answer
The simpliest schematics is probably amplifier from any ion smoke detector. Connect base of n-p-n darlington (the one without internal resistors) to metal box and emitter to ground. Apply 50% of transistor rated c-e voltage (10..20v) through 1..10k resistor with LED.
For fun, try 4-6 transistors in enourmous darlington chain with LED. It will work like "detector of everything". In my experiment it detected a lit match few feet away with "antenna" 1 inch long. (Sorry no proof of working in vacuum due to budget limitations)