Browse Prior Art Database

Circuit for Detecting Connection of Device to a Controller

IP.com Disclosure Number: IPCOM000086744D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Lynch, E: AUTHOR [+2]

Abstract

The drawing shows a device 2 that may be used for entering a personal identification number into a data processing system to permit an operation such as transferring funds from one bank account to another. The device has a cable 3 with a plug that permits it to be connected to a controller 5. Also, it has a light-emitting diode (LED) 6 that is turned on by the controller to signal to the user of the device that an entry can be made.

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Circuit for Detecting Connection of Device to a Controller

The drawing shows a device 2 that may be used for entering a personal identification number into a data processing system to permit an operation such as transferring funds from one bank account to another. The device has a cable 3 with a plug that permits it to be connected to a controller 5. Also, it has a light- emitting diode (LED) 6 that is turned on by the controller to signal to the user of the device that an entry can be made.

The controller includes a driver transistor 7 that turns on in response to a signal on a line 8 to turn on LED 6. The circuit of transistor 7 and LED 6 includes wires 9 and 10 of the cable 3, and the circuit is open when the device is disconnected from the controller.

It is desirable to provide a signal that indicates whether device 2 is plugged in to controller 5. As shown, a transistor 12 is connected to sense the voltage at conductor 9 and to produce a signal, DEVICE PLUGGED IN, at its collector terminal. Transistor 7 is turned on for the operation of detecting the connection of device 2 to controller 5. When the device is unplugged, line 9 is disconnected from the source of voltage for LED 6, and transistor 7 conducts, in circuit with resistors 13 and 14, to turn off transistor 12. When device 2 is plugged in, the base terminal of transistor 12 receives the voltage of the source minus the fixed drop across the LED, and transistor 12 remains on.

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