need help about sensor


Joined May 20, 2006
Do you need to measure individual coins, or just check that they match valid coins' range ?

IIRC, coins' densities are usually checked by slot(s), which constrain by volume of thickness x diameter. Then there is the mass, checked by a sprung lever or similar 'scale'. A magnet may accept / reject certain coins, a coil facing a magnet could respond to eddy currents depending on the alloy etc etc.

I'm sorry, the only absolute density method I can think of involves weighing the coin then using Archimedes' principle and carefully measuring the volume of water it displaces...

If you don't have to worry about hidden voids or damaged edges, just measuring the coin's weight, thickness & diameter should get close...


Joined Jul 26, 2010
Read up on how a coin accepting device works in a vending machine, most still rely on mechanics.

While mass is easy to sense it gets a bit more difficult to calculate the actual volume of a coin, due to the way they're stamped the simple principle of measuring diameter and thickness doesn't give accurate results.

Coin acceptors simply accept the fact that they're going to get fooled on rare occasions but rely on the fact that it really isn't worth all the time and trouble involved in producing replicas that will fool them.

What are you trying to build?