delabs circuits
delabs circuits

delabs circuits

Electronic Engineering Schematics

Home - Circuits - Embedded - uC Interface - Serial 7135

Serial Interface 7135 to 8751 Reads Analog Values

Using a ICL7135 A to D Convertor with a Microcontroller is easy with the Serial Interface. The advantage is you could use an Opto Coupler to protect your Embedded System.

uC Input and Output I/O is Keyboard and LCD when you build a Calculator or a Text/Morse Communicator. When you control a motor it is Drive/Speed and Direction for Motor and Tacho or Opto Counters for Feedback. In both cases you have Input and Output which is Logic or Analog which has to reach the CPU.


Getting the analog into the uC is done here with ICL7135, with a simple two wire serial interface. Here a Pair of CD4538 MMV is used to shape the pulse just right for uC data transfer,

ICL7135 Intersil, 8751-8031-8951, the circuit for uC chips are not drawn in the circuit below as they are in other circuits. See datasheets or application notes too.

The Busy signal and clock when anded (AND) will give a burst of pulses. Count them and deduct 10,001 from the virtual uC counter.  ICL7135 4 1/2 digit A/D DPM Chip

CD4538 Monostable Pulse Shaping Circuit

PNG-Schematic  -   PDF-Circuit   -  Source

Serial Interface 7135 to 8751 Reads Analog Values - del20001

To view circuit above, Click the Link of PNG or PDF, PNG can be Drag Scrolled with Mouse

U2B sends a short interrupt pulse to uC which means 'busy' of 7135 has gone from high to low and reading in counter of uC is valid, also reset counter to 0 for new reading next time 'busy' goes high. count the clock and substract 10,001 from that, you got a reading.

BUSY 'AND' CLK '-' 10,001 '=' READING

ICL7135 Pin 11 +5V, Pin 1 -5V, Pin 24 digital GND

SDCC - Small Device C Compiler

The input of ICL7135 has to be protected from Overvoltage both negative and positive. This is done by a Clamping circuit made of two back to back low leakage Zeners. Some zeners may leak more, see the datasheet. Use Ordinary Diode clamping circuit with 2 nos 1N4148 in series to the + and - rails. Change ICL7135 to 200mV FS for Diode Clamping.

          Diode Voltage Clamping Protection

ICL7135 to Printer port Interface - Here you can see a Parallel Port Interface to a A/D Converter. You could experiment in a older PC. Or use a Parallel Port Card in a New Desktop PC. USB now is the only wired PC Interface today. LAN is an old port but has never found a use in peripheral Interface, but is changing now in the DIY world.

HDMI for HD Multimedia is now Standard in most PC and Laptops, DIY Enthusiasts have not found this as interesting as the Wireless Interfaces like Wi-Fi (wireless lan) and Bluetooth. Bluetooth is glitchy, now things have improved a bit. IR Interfaces have been there but not many takers.
Back to Analog and Digital Interface 80C51







delabs Technologies

20th Apr 2020


Disclaimer and Terms of usage

The documents, software, tools and links are provided to enhance the ability of an electronics student, hobbyist or professional by sharing information. The information, links etc. should be used by the website visitor, at his or her own risk and responsibility. There may be concept, design and link errors in the pages.

Creative Work, ideas and documents of delabs can be used for Product Design and Development by R&D Engineers, Hobbyists, Students and even firms for creating useful products. These cannot be used for reprint, replication or publishing online or offline.