Electronic Engineering Schematics
ICL7135 to Printer port Interface - del20002
A PC based Analog Voltmeter. The Printer Port or Parallel Port
Interface is used to acquire high resolution analog data using
ICL7135. This is a method of getting analog data into your PC.
This is only of Educational Value. Applications include Data
Loggers and PC based Process Monitors, chart recorders. (USB,
Wireless Interfaces and Tablet Computers are in vogue
The ICL7135 details can be seen here 41/2
A/D with BCD ICL7135
. This Mixed device was far ahead of
its times, a product of Intersil,
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.
to Printer port Interface - del20002
To view circuit click the Link of PNG or PDF, The PNG
Image can be Drag Scrolled with Mouse.
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.
and Digital Voltmeter using ICL7107
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
. 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
Back to Analog Interface for PC
20th Mar 2020