Browse Prior Art Database

Ground Checking Circuit

IP.com Disclosure Number: IPCOM000051075D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Lisica, VM: AUTHOR [+2]

Abstract

In a printer using grounded metallized paper, printer electrodes can be checked for contact with the paper by connecting each through a diode to a common current-limiting resistor and sensing the potential at the diode-resistor junction.

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Ground Checking Circuit

In a printer using grounded metallized paper, printer electrodes can be checked for contact with the paper by connecting each through a diode to a common current-limiting resistor and sensing the potential at the diode-resistor junction.

Referring to the figure, electrodes 1a-1n, each in apparent contact with grounded metal coating 2 on paper 3, are connected to a negative power supply at point 4 through individual diodes 5a-5n, all connected to a common current- limiting resistor 6. A sensing circuit is comprised of resistors 7 and 8 and capacitor 9, with their junction providing an output level at B indicative of the contact status of the electrodes. Transistor 10 is turned off by a control signal at its base circuit 11 when electrode checking is to occur.

Diodes 5a-5n form a logical OR of the grounded condition. Wire drivers 12a- 12n are deactivated during this checking phase. When ground is present at any anode of the diodes, the cathode will clamp at a negative voltage equal to the drop across one diode at point A as long as transistor 10 is off. If ground is not present at any one or more of the diode anodes, the voltage at point A will be more negative. Diode 13 from sensing transistor 14 will be forced to conduct, and the voltage level at point B will now be slightly negative.

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