Installation guide
Coin acceptors: how they identify a coin and how to teach them a new one.
A coin acceptor is a measuring instrument with a gate on the end. Understanding what it measures makes both programming and fault-finding straightforward, and explains why the same unit behaves differently in two countries.
A multi-coin acceptor identifies a coin by measuring its diameter, thickness and alloy signature as it rolls past a sensor, then comparing those values against stored samples. Comparison-type units store a physical sample coin; CPU types store the values electronically and are taught by inserting the same coin fifteen to thirty times in programming mode. On a valid coin the unit closes a switched output for a few tens of milliseconds — one credit pulse — which the game board counts.
Comparison type versus CPU type
A comparison acceptor holds a real sample coin in a cradle inside the unit and measures every inserted coin against it. Changing what the machine accepts means physically swapping the sample. It is simple, cheap and hard to get wrong, but it handles one coin or token at a time and drifts as the sample wears.
A CPU acceptor stores the measurements electronically and can hold several coin types at once, each with its own credit value — useful where a machine has to take two denominations, or a coin and a house token. Programming is done through a button and a display or LED sequence on the unit rather than by opening it up.
Teaching a CPU acceptor a new coin
The sequence is broadly the same across CPU units. Enter programming mode with the button on the front, select which coin slot is being taught and how many credits it is worth, then insert the same coin repeatedly — fifteen to thirty times is typical — so the unit can average out variation between individual coins. Save and exit, then test with coins the unit has never seen.
Use circulated coins for teaching, not fresh ones. A sample averaged only from mint coins tends to reject worn coins in service, which is the single most common cause of an acceptor that worked on the bench and rejects in the field.
The pulse output and how the board reads it
On acceptance the unit closes a contact briefly — commonly around 30 to 100 milliseconds — and that closure is the credit signal. A coin programmed as worth several credits produces several pulses in sequence rather than one longer one. If the machine counts too many credits per coin, the credit value stored against that coin is usually the cause, not the board.
Wiring is typically three connections: supply, ground and the pulse line to the coin input on the game board or JAMMA harness. Check the supply voltage the unit expects before connecting; 12V DC is common but not universal, and units also differ in whether the output switches to ground or to supply.
False rejects and false accepts
A unit that rejects good coins is usually dirty, misprogrammed from mint samples, or mounted out of vertical. The coin path has to be clean and the unit close to plumb, because the measurement assumes a predictable roll. A sensitivity adjustment exists on most units, but cleaning and reteaching fixes more cases than turning it does.
A unit that accepts slugs or foreign coins has usually been taught too tolerantly — sensitivity set wide to stop rejects, at the cost of discrimination. Where a machine is taking losses, narrowing sensitivity and retraining on circulated coins is the fix; a token-only setup with a distinctive house token removes the problem entirely.
| Aspect | Comparison type | CPU type |
|---|---|---|
| Coin types held | One at a time | Several, each with its own credit value |
| How it is taught | Swap the physical sample coin | Insert the coin 15–30 times in programming mode |
| Adjustment | Sensitivity dial | Sensitivity plus stored parameters |
| Best for | Single coin or single token machines | Mixed denominations, multi-market machines |
Frequently asked questions
How does a coin acceptor tell coins apart?
It measures diameter, thickness and alloy signature as the coin rolls past a sensor, then compares those values against a stored sample — either a physical coin in a comparison unit or saved values in a CPU unit.
How do I program a new coin or token into a CPU coin acceptor?
Enter programming mode with the front button, choose the coin slot and its credit value, then insert the same coin 15 to 30 times so the unit can average the readings. Use circulated coins, not mint ones.
Why does my coin acceptor reject valid coins?
Usually a dirty coin path, a unit mounted out of vertical, or a sample taught only from mint coins. Clean the path and reteach with circulated coins before adjusting sensitivity.
What signal does a coin acceptor send to the game board?
A brief contact closure — typically 30 to 100 milliseconds — for each credit. A coin worth several credits produces several pulses in sequence.
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