Years ago, I made a free play device for my Exidy Collen'x. Before people chime in and say it already has a free play, you are correct... with a catch (but, that's for another discussion). Now, I can't claim this is original, but it's what I made. I needed a couple more and since having 30 pcbs made were the same price as 10, I had 30 made, they sent me 50. I needed more due to some games free play just sit on a static screen.
First, I'm gauging interest in an independent free play addon. It's a rather simple device, about the size of a quarter, that only needs +5v, gnd and connection to coin and 1/2 player start. It is a very limited device. Press and hold 1p button for ~2-3sec and it triggers a coin. Hold 2p button for ~2-3sec and it triggers 2 coins. It won't trigger anymore coins while the button is held. If you let go and hold it again, it will trigger in another credit or 2. Like I said, Simple. Most games will automatically start once the coin is added, others will wait for the start pulse from the device. I've tried it on Dig Dig, Centipede, Galaga, Ms. Pacman and, of course, Exidy Collex'n. Ms. Pacman worked, but, since it had a two bit score multi-game, it automatically started the same game all the time. This would be a limited run and would only have, maybe, 40 available. I have enough parts for my purposes and will have to order more parts if people are interested in them. I'm not looking to get rich off of these, so I would sell them for near cost + shipping. Initial cost estimate would be $8-$10? for each device and USPS Priority mail is about $10. Cost for the device might be less if people don't want the quick screw connectors and just want to solder the connections themselves (est. $6-$8?). If interested reply to this thread with how many and opinion on quick screw connectors. Right now, this is merely an interest check.
Second, I'm looking for a tester. Someone of my choosing, trusted in the community, that has several games that he/she would be able to test in a reasonable amount of time, 1-2 weeks, and give feedback, must have an Eprom burner capable to burning PIC Mircro-controllers (should the code need to be updated), be able to solder and live in the continental US. The person chosen for testing will be shipped 1 device to test and keep (won't have quick screw connector). If you are interested, please pm me.
If there is little to no interest, no worries. I had the pcbs made for my purposes and have extras. What I don't have is enough microcontrollers or screw terminals and would have to order them, if there's an interest.