| 摘要 |
A vending machine door switch interface allows multiple controllers, including the vending machine controller, to employ a single door switch without polarization or interference. The interface includes a comparator having inputs coupled across the door switch and, based on the door switch state, produces an output signal indicating whether the service door is closed or open. The comparator output when the service door is known to be open is recorded to subsequently distinguish open and closed states. Unbalanced connections to power and ground result in different voltages at the comparator inputs when the door switch is closed.
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