I ordered the dual optical sensor that my Babel uses. Will take a few weeks to come from China. Will keep you posted with the outcome. If successful I'll probably make a circuit to increment the credits by 10 everytime a quarter is inserted. Probably some sort of microprocessor. It will also accomidate coin speedloading since it takes a few seconds to register 10 credits. The original circuit had a lead going to the coin hopper cable that was hacked off. Not sure if that was a sense lead or a control lead. During a jackpot with the credits at 50, it should eject coins and may actually want to count them on exit to verify the correct payout. I know there are hopper sensors such as hopper empty and hopper jam. For what I can tell without actually seeing one is that it has a spinning disk that coins fall into which has a stepper motor rotating it and quite conservatively, coins might not fall into the rotating disk holes, short changing the payout so some sort of feedback is required to keep the count accurate.