Driving 8 7-segment dusplays with few data lines

[poorchava]

I need to multiplex 8 7-segment displays + some leds (device panel). The problem is that i've got very limited number of data pins available for display.

Displays which i'm using are common anode, single display dies (bought them in large volume for an attractive price). I want to drive segments with serial-in-parralell-out registers 74hc164. This approach uses only 2 pins of microcontroller.

I don't know what to use to drive digits. I thought about cd4017 decade counter or cd4028 bcd-to-decimal decoder, but none of them can source enough current to drive a display with sufficient brightness. I could use some darlington array line ULN2003, but it needs to be pnp type, which is far less common and like 5x more expensive than ULN type (ULN's are npn only).

I could use shift registers for driving digits too, but i'm worried about display flickering. Has anybody tried using shift registers for driving both segments and digits?

The microcontroller i'm using is AVR (protptype is on atmega8, but final design will use atmega48-10 (the 10MHz version) in tqfp package.

 

[hugo]

Hi,

You can use a HC595 shift register ic . You 're going to need 8 pins for driving the anodes ( trough some transistors , hc595 outputs to 7 segments ) 3 pins to control HC595 CLK,DATA,OE & LATCH together for brightness control ( AVR PWM OUT to OE & LATCH ) ... clk and data lines could be also shared ( 2 of the 8 anodes lines )

 

[abidr]

Have a look at the link, its a video showing Binary and Decimal clock.
The clock uses an Atmega16 and drives 6 7 segments and about 24 LEDs, using 6 shift registers.
Drop a message to remus, he is more than helpful perhaps one of those few people who are not afraid to share their firmware and source codes, if you need any further help drop me line here.
YouTube - Binary and Decimal Clock

 

[DineshSL]

Hi poorchava,

Did you try 7 segment display driver (SSD) ICs; Normally input of them are clock signal or binary, so very few input pins are required.

eg:
4026
4511
7446
7447
7448
7449

Hope this helps you,

 

[masifshahzad]

try MAX7219CNG.

 

[horace1]

there are LCD displays with I2C and SPI interfaces that can be connected to common microcontrollers.
For reduced pin count probably I2C is the best as it is two wire and devices are identified by an address but you may have problems using a number of the same device; SPI requires four lines clock, data in and out and enable (which you could multiplex to address a number of devices)