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Automatic Lamp Test

IP.com Disclosure Number: IPCOM000085231D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Humphrey, RB: AUTHOR [+2]

Abstract

Existing lamp test schemes require a switch to cause a large number of lamps to turn on at one time, a power supply capable of driving all of the lamps, and an operator to visually check for burned out lamps. In computer control of machines, the computer can normally be utilized to drive the lamps. In the example given, the lamps are light-emitting diodes (LED's) but the scheme described below is also useful for photocell illuminators as well as normal indicator lamps.

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Automatic Lamp Test

Existing lamp test schemes require a switch to cause a large number of lamps to turn on at one time, a power supply capable of driving all of the lamps, and an operator to visually check for burned out lamps. In computer control of machines, the computer can normally be utilized to drive the lamps. In the example given, the lamps are light-emitting diodes (LED's) but the scheme described below is also useful for photocell illuminators as well as normal indicator lamps.

Referring to Fig. 1, the LED's I1-I8 are turned on one at a time by the 7417 drivers A1-A8. When an LED is turned on, current flows through resistors R1 and R2. The current flow through R1 and R2 drives the base of transistor Q1 negative with respect to the emitter, and inasmuch as Q1 is a PNP transistor, it turns on.

Turning transistor Q1 on causes current to flow through resistors R3 and R4 and the input to the 7414 Schmitt trigger goes high. The output from the Schmitt trigger goes low, indicating that a LED is turned on. With no LED on, Q1 is turned off and the input of the Schmitt trigger is accordingly at ground level so its output is high. The output of the Schmitt trigger will also be high if one of the 7417 drivers turned on, but the corresponding LED is burned out or not plugged in.

Assuming that the transistor Q1 and its associated resistors R1-R4 are connected as shown, and referring to those active and passive devices as the current sensor, Fig. 2 illustrates the LE...