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AT89C52 Parallel Interface to ICL7135

This circuit is a Parallel 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.
Using Linux in Embedded Electronic Devices

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.

Parallel interface is faster that a serial interface.It is more "Real Time" for a given processor and clock speed. The code and accompanying hardware also can speed up the data acquisition.   

AT89C52 Parallel
                        Interface to ICL7135

PNG-Schematic     PDF-Circuit   -  Source
AT89C52 Parallel Interface to ICL7135 - del20025
To view circuit above, Click the Link of PNG or PDF, PNG can be Drag Scrolled with Mouse

ICL7135 Pin 11 +5V, Pin 1 -5V, Pin 24 digital GND, add a decoupling 104 CD cap from +5 to GND and -5 to GND
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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.     

MAX232A PC Serial Port

A single maxim chip can act as a good interface between the uC and Serial Port. You could also do this with Logic chips but correct levels and isolation cannot be achieved, Hence better to use use these interface chips.

These days USB and Wireless Interfaces are being used and Tablet Computers becoming Popular. The Interfacing of the future is "Device Networking" and Wireless may be common.