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interfacing seven segment display

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abhignans

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hello ,everyone.

im doing a temparature display using pt100 and pic18f452.

i am using 8 pt100 sensors, ie..8 channel inputs..

i want the temparature to be displayed on the seven segment displays

so for that to do i need atleast 2 seven segment displays for each channel

1pt100 sensor=2 seven segment display(atleast)
for 8 pt100 sensors = 8*2=16 segments

so for interfacing this i am using multiplexing technique. but even after using this technique i am not able to interface because the pins are not enough because


i have 8 analog inputs for pic and they being used for inputs
and four for bcd to seven segment and 16 for each digit
and i am left with 4 pins
and stiil i need pins for displaying negative led for temp and the pins are not enough.
please help me any technique to interface these seven segment displays
thank you.
 

BradtheRad

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It sounds as though you are using 16 pins to activate 16 digits one at a time... correct?

The 74154 is a 4-line to 1-of-16 decoder IC.

You send a binary number to 4 pins. It pulls one of 16 pins low.

I believe it will free up 12 pins on your pic.
 

ZASto

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If you use 74HC595 you need only 4 pins of your uC (SerialData, Clock, Latch, OutputEnable) and you can cascade as many displays as you wish, no mind bogling multiplexing etc.
 

jpsganesh

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Well said Mr. BradtheRad.

Other option u can use scroll type only using 3 or 2 seven segments.

If u wants to use 3 7-seg method then fist segment for displaying the sensor no and next 2 segments for displaying the temp of that particular sensor. Accordingly place first segment and next two segments with little bit space.

If u want to use 2 7-seg method then u need to use 8 individual LEDs or LED array to display the sensor no. and the 7-seg can be used to disp the temp.
 

abhignans

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thanks Mr. BradtheRad

74154 pulls only one segment to low at a time but for multiplexing i need all segments to low and the display which has to be changed shud b high....im little bit confused again:-?can u suggest me how to do it

- - - Updated - - -

yes tat's a good idea mr.jpsganesh but im doing this for a friend who want to c all the displays and compare them so i cant use scroll type..
anyways thanks for the suggestion
 

BradtheRad

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thanks Mr. BradtheRad

74154 pulls only one segment to low at a time but for multiplexing i need all segments to low and the display which has to be changed shud b high....im little bit confused again:-?can u suggest me how to do it

1.

In that case there is the 4514 IC (1-of-16 decoder/demultiplexer with input latches). The decoded pin is high.



2.

You can add an inverter gate after all 16 output pins of the 74154 or 74LS154. You would need 3 hex inverter IC's. (Two gates would be left over.)

3.

It is also possible to construct a 1-of-16 decoder from two 3-line to 1-of-8 decoder IC's (74138, 74LS138).
(You would need to add 16 inverter gates on the output pins.)

https://ecee.colorado.edu/~mcclurel/sn74ls138rev5.pdf

4.

This Edaboard thread talks about using 2-line-to-4-out decoders.

https://www.edaboard.com/threads/124668/

5.

A list of multiplexing/demultiplexing IC's is at this Wikipedia page. (It shows the 74159 as a counterpart of the 4514 IC.)

https://en.wikipedia.org/wiki/Multiplexer
 
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