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ICL7135 to Printer port Interface - del20002The ICL7135 details can be seen here Device Information of ICL7135 . This Mixed device was far ahead of its times, a product of Intersil, See History of Intersil at Wikipedia.The four Digit Drive outputs and four BCD outputs of the Multiplexed Display Driver of 7135, along with A-D status output which is also four, are routed to four input pins on printer port via three 74HCT373 Digital Switches. This is because we have less Input pins on Port and 4 are shared by making one 74HCT373 transparent and others High Impedance when PC takes a reading. So the three sets of four outputs of 7135 can be read sequentially. 74HCT139 U9A which is controlled by the PC program can select U3, U4 or U5 for sending data to 4 pins on printer port. Data sent on the eight output pins of printer port can be latched by U10B into U6. This eight outputs of U6 can drive relays or lamps. To view the circuit below, Click the Link of PNG or PDF and view the Circuit, PNG can be Scrolled with Mouse and PDF can be Viewed-Zoomed in the Browsers with Acrobat plugin. The Javascript and Images must be enabled in your Browser. |
| PNG-Schematic
PDF-Circuit DSN-Source |
| ICL7135 to Printer port Interface - del20002 |
| PNG
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The Design source files in Orcad Capture 9 format is here 20002.zip. A example VB program with source to test above circuit with PC is here, Visual Basic Digital Voltmeter. This program may not be error free but works. When you build above circuit and voltmeter on PC. Use it only with 5V battery projects. Any high voltage goes to printer port due to wrong connection you may lose a motherboard or worse. Better isolate all data lines to port with opto couplers if you want to build this for regular use. |