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@ 2009/08/10A tachometer is usually installed in a car to measure the rotation speed of the engine. but I was going to use it to display the level of CPU usage. I bought the tachometer on Ebay, from a Chinese seller. I paid it only £20 delivered but I can not say it is a top quality device. Though It does its work it is very plasticky and the needle movement isn’t very precise.
The tachometer connects to the PC through 3 wires: 2 wires for the 12V power supply (the red and the black wires), whilst the green wire carries the signal which drives the needle. If the tachometer was installed in a car the signal would be a square wave coming from the engine coil: the higher the frequency of the square wave the further the needle moves. I wasn’t sure about the required amplitude of the signal but I found out that 5V were just right.
The tachometer connects to the PC through 3 wires: 2 wires for the 12V power supply (the red and the black wires), whilst the green wire carries the signal which drives the needle. If the tachometer was installed in a car the signal would be a square wave coming from the engine coil: the higher the frequency of the square wave the further the needle moves. I wasn’t sure about the required amplitude of the signal but I found out that 5V were just right.
