AT89C52 Parallel Interface to ICL7135

This circuit is an interface between 89C52 of Atmel with 7135 of Intersil. With This circuit you can read analog data of both polarities you can change the range scale with extra circuits, you can store data on a EEPROM or send them to PC thru RS232 or Comm port.

The Circuit Is Shown for One Anode Drive and one Segment Drive for Display. In similar Fashion connect rest, all 5 anodes and 7 segments and one dp decimal point. The +5 V of 2N2907 and gnd of BC547 must be directly from regulator with a big cap or even a separate supply.

7135 is a A-D converter, datasheet Intersil.

AT89C52 is a Microcontroller & Flash Atmel

Firmware :

The example code for display drive, comm port has been given in the other projects on this site. So I will just explain how you can get the data from 7135.

Initialization :

Set Port 0 and Port 1 all pins high by writing ones. enable INT1

Data Acquisition:

On INT1 interrupt Check the state of P 0.4 or D5 digit 5 of 7135.

if P 0.4 is low then do not do anything.
if P 0.4 is high then read Port 0 and store them in say D5VAL "value of D5".
Also in a place say DIGCNT "digit counter" store the number 5.

now interrupt occurs again .....
decrement DIGCNT to 4
AND Port 0 value store in D4VAL.

.......... this goes on till DIGCNT comes to 1 then you got all the data.

Lower nibble of Port 0 contains the BCD value of the digit.
Digit 5 is MSD and Digit 1 is LSD.
Upper nibble contains polarity, over range and under range.

P1.2 can be used as an output port to RUN-HOLD the 7135 if you want.
Keep it low to hold and a high pulse to get one reading or keep it high to keep reading.