I was just looking at the PIC capmeter thread and thought I'd dig this little baby out... thought some of you might find it interesting.
It's a capacitance meter I designed when I was a teenager close to 30 years ago, when there weren't many available and they were way out of my price range.
This particular one was built around '85.
It's based on a 555 timer. The timer outputs pulses whose width varies with the capacitance connected, the pulses then gate a clock which is counted by a 3 digit BCD counter IC and displayed on an LED through a BCD to 7 seg decoder. A quad nand gate is used to develop reset and latch pulses, and a second 555 stretches the reset pulse to zero the meter.
I saved money by using the counter chip's built in multiplexer as the clock signal, and the small LED was driven directly by the chips, no buffers or current limiting resistors.
It has 2 ranges, .001uF to .999uF and 1uF to 999uF. I did have another version that would display picoFarads by dividing down the 555 pulses.
Altogether it probably cost me $15 to $20 in parts availabe at Radio Shack at the time.
It's a capacitance meter I designed when I was a teenager close to 30 years ago, when there weren't many available and they were way out of my price range.
This particular one was built around '85.
It's based on a 555 timer. The timer outputs pulses whose width varies with the capacitance connected, the pulses then gate a clock which is counted by a 3 digit BCD counter IC and displayed on an LED through a BCD to 7 seg decoder. A quad nand gate is used to develop reset and latch pulses, and a second 555 stretches the reset pulse to zero the meter.
I saved money by using the counter chip's built in multiplexer as the clock signal, and the small LED was driven directly by the chips, no buffers or current limiting resistors.
It has 2 ranges, .001uF to .999uF and 1uF to 999uF. I did have another version that would display picoFarads by dividing down the 555 pulses.
Altogether it probably cost me $15 to $20 in parts availabe at Radio Shack at the time.
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