Coin mechanisms and coin door

The coin door

The coin door was a bit rusty and beaten up when I bought the cabinet. I sanded it down and gave it several layers of a black matte paint, and it came out pretty nice. Tie picture also shows the keychain with my SpiffMAME logo (printed on my new Samsung CLP-550). For those who know anything about the danish currency, you may think the pricing is fairly cheap. This is intentional, since I wanted a more authentic setup from the 80's and 90's. That is also the reason why I mostly play the older classical games, such as Frogger, Lode Runner, Up 'n' Down etc.

The inside of the coin door

The inside of the coin door has mounting brackets for two coin mechanisms. The coin mechs in this picture are the ones that were in the cabinet when I bought it. Although they work, they are not flawless, since they were originally made for other coin sizes (the 2kr unit was originally for US quarters), and hence heavily modified to accomodate the danish coins. This also means that several of the comparison features of the mechs have been circumvented, in order to make the unit accept the coin. I have spent a great deal of time trying to find some new coin mechs. Happ Controls have a mechanism for danish 5-kroner pieces, but not one for 2-kroner (since this is rarely used anymore).

Old coin mechs

The image above shows the heavily modified coin mechs found in the cabinet when I bought it. They are far from reliable, so they will need to be replaced (although I hardly ever enable the coin slots, and I think I am the only one who ever put money in the machine, I still like everything to work. It actually adds to the feeling of nostalgia and authenticity to hear the coin go through the mechanics and drop into the safe on the bottom of the machine).

New coin mechs/equlizers

I finally gave in and sent an E-mail to Happ Controls asking for a 2 kroner coin mechanism. They forwarded the mail to Suzo International (with whom they are now partnering), and I ended up buying a set of coin equalizers (CE-100). These units are purely electronic. They have a small spring-loaded bracket where you mount a coin of the kind you want the unit to recognize. Then all that needs to be done is to supply the unit with 12V (which can be taken from the PC power supply in my case, and you are all set to go.

The units are supposed to be plug-in replacements for old coin mechanisms, and concerning the size and shape, they fit nicely into the brackets on the inside of the coin door. Unfortunately this new electronic unit drops the coin straight through (if it matches), so the speed it passes the switch with is too high for the keyboard controller to handle it. This means you only get a credit about half of the times you drop in a coin. However, the units also have a digital output that gives a pulse when a coin is accepted. The signal level of this output is, however, not compatible with my keyboard encoder hack, so I will need to take a different approach to make this work.

I am working on a home-built keyboard encoder, custom made for use in SpiffMAME, but at some point I decided to make the new coin-units work even with the old keyboard-hack. This was accomplished by using a 4066 Quad Analog Switch, which is powered by the 12V supply from the PC (also powering the coin units). The outputs of the coin equalizers are open collector, so adding a pull-up resistor to 12V provides the analog switch input with an appropriate signal. The coin equalizers have both normally open and normally closed outputs, so no inverter was needed. Now, when the coin is accepted by the coin equalizer, the analog switch is opened for a short amount of time, allowing the analog switch to be wired to the keyboard controller as if it was a normal switch, like the one on the old mechanical coin mechanism.

Schematic of the coin-unit interface

The figure above shows the circuit diagram I used for interfacing the new coin-units to the keyboard controller. As you can see I have a jumper for each of the coin-inputs to select if it should be normally open, or normally closed. Also notice how the circuit is powered by 12V. Since the voltages on the swiches of the 4066 sould be within the supply voltage, and the keyboard controller uses 5V, this works fine. Actually I could equally well have used 5V for the 4066, since the outputs from the coin-units are open-collector.

The new coin-units and interface-circuit

The image above shows the new coin-units mounted inside the coin-door, along with the circuit to interface to the keyboard controller, made on a small piece of prototyping PCB.

Since the new units do not have a lever for releasing jammed coins (aparently they are constructed in a way where coins cannot jam in the mechanics), I have been thinking about putting a switch on the coin release button. When enabled, this will give one credit when depressed. In this way I can avoid having to open the coin door all the time to get credits.

Last updated: 2005.10.15