Instructables

Hard Drive Tachometer for a Desktop Computer

Interface.BMP
brd.BMP
Inter.BMP
Tired of the old boring Hard Drive indicator LED, one puney LED.
Then one choice is to add a HDD ( hard drive ) Tachometer.
This tach will show the HDD activity on a desktop computer. Not for automotive use.

Built with the 555 and 4017 combination. But the " Interface " is what makes this work.
Tricky thing is the HDD LED has full V+ all the time and it is the ground that is varied to make the LED flash. 
That means the HDD LED ground becomes the input signal for the tachometer, or pin2 of the 555.
There is more descriptions in the pictures.

I did not go in-depth of the chip operations and theory, just a down and dirty hack.
Actually i do not know exactly why / how the interface works or why it works.
Somebody with a physics or electronics background could probably understand and explain how this works. 
For me,   IT WORKS.

My regular camera is not here so the pictures are, well not good.
iceng1 year ago
Ahaaa a Hard Drive.

Sorry for my ignorance.
WWC (author)  iceng1 year ago
No problem.
I changed the title and an HDD explanation in the content.
iceng1 year ago
HOW do you know, when you drive at 15 mph ?
What does your tach show ?
WWC (author)  iceng1 year ago
15 mph have to be shown of coarse on a speedometer in a car.
This shows the HDD activity of a desktop PC.
Did i write it to seem that is was a car tach?