Coin Mechanism for Central Vac

Can anyone point me in the direction of a company that makes coin mechanisms for individual vac drops from a central vac system?

I want to be able to charge for vac time but I need the noise contained to inside the building.

i used a coinbox from a selfserve vac mounted to a pole a while ago but i ran one drop off for a super vac $2.50 for 4 minutes people loved it ran it till the vac died then retired it but it made a few thousand dollars. Used a regular timer and and hookeed it to the motor starter as a remote function.

Seems like you'd need a valve to control the flow to the hose - assuming your central vac will run continuously, any old vac timer and acceptor in a box to control the valve will do.