I'm designing myself a "simple" continuity tester. There will be a 200 ohm pot on the PC board that will be the "resistance standard". A PIC processor will apply voltage across the pot and measure the analog voltage on the wiper. Then it will apply voltage to the unknown resistance on the input leads and measure the voltage drop across that resistance. If the voltage drop across the unknown is less than or equal to the voltage across the pot's wiper, then a signal will turn on (either an LED or a piezoelectric beeper or both). A DIP switch will allow you to invert the sense of the test. Basically, I want a continuity tester that lets me adjust the definition of "continuity". There will be some pulse stretching in software to help find those momentary shorts.
I intend to use this for quick troubleshooting around the bench, the house, and the car. It will be in a small package that easily slips into a pocket so that it's handy to carry around. I also have a small analog meter (10 mm in diameter and 15 mm long) that I will use to make DC voltage measurements up to 15 volts.
I would like to protect the microcontroller's input lines in case I accidentally put it across a significant voltage -- say, up to typical US line voltage levels. If I were to use a fuse, it would probably have to be a fast-blow fuse rated to around 10 mA or so (and I don't know if such things exist). The problem with a fuse is that if it blows in the field and you don't have a spare, you're shut down until you can get one. I was hoping there would be a simple and low power method of protection
Question: what method would you folks recommend to protect the input line?
I intend to use this for quick troubleshooting around the bench, the house, and the car. It will be in a small package that easily slips into a pocket so that it's handy to carry around. I also have a small analog meter (10 mm in diameter and 15 mm long) that I will use to make DC voltage measurements up to 15 volts.
I would like to protect the microcontroller's input lines in case I accidentally put it across a significant voltage -- say, up to typical US line voltage levels. If I were to use a fuse, it would probably have to be a fast-blow fuse rated to around 10 mA or so (and I don't know if such things exist). The problem with a fuse is that if it blows in the field and you don't have a spare, you're shut down until you can get one. I was hoping there would be a simple and low power method of protection
Question: what method would you folks recommend to protect the input line?