One technique would use a Programmable Logic Relay (PLR).
Bill acceptors utilize pulses to trigger the timing device…4 pulses per dollar. These pulses are typically 10ms On, 10ms Off. Therefore, a $5 bill will deliver 20 pulses in 4 seconds…faster than the user can insert 5 $1 bills.
The PLR monitors the acceptor’s output pulses. If the 20 pulses require longer than 4 seconds, nothing happens. If the 20 pulse count takes less than 4.1 seconds, the PLR’s output for that bay is triggered, sending additional pulses to the timer. Bonus time!
You can even establish “Happy Hour” days and times when bonus time is provided!
One Siemens LOGO!/Idec Smartrelay (PLR) can provide this bonus time feature for up to 4 bays. With an I/O expansion module, the bay count goes to 8. A 2nd thru 5th generation PLR can be purchased rather inexpensively on eBay. The current model sells for around $145. Idec’s FL1F-B12RCA is 24v AC/DC powered…ideal for car wash control systems (no DC power supply or interfacing relays required.)
http://us.idec.com/Catalog/ProductS...L1F_SmartRelay&FamilyName=Programmable_Relays