0

I'm making a project and I'm using multiple 1 digit 7 segment displays. I haven't plugged them all on my arduino because currently I'm just testing. The problem is on the I/O ports. Obviously I need to use shift registers and since it's my first time ever using them I need to know more about them. After googling, I found that the specific model I bought outputs 8 pins and you can stack up to 8 in series. So lets do the math. 8 shift register x 8 pins each SR = 64 new pins It seems cool but assuming I'm using 28 displays let's do the math again. 28 displays, each display has 8 pins (8 for segments and 2 as common cathode) 28 x 8 = 224 required pins. Is is possible to expand the I/O pins by 224 pins? How many shift registers can I stack together? Also which is better, the single digit display or the 4 digit display?

2 Answers 2

4

You can chain as many shift registers as you want.

Most commonly, these displays are multiplexed. Only one digit is lit at a time, cycling though all the digits fast enough, so the eye can't tell. This is however not very good practice for 28 digits, as the brightness will become 1/28th (though you could create groups of digits, and multiplex those groups separately).

There are specialized chips that do this multiplexing for you. E.g. the Max7219. This chip can multiplex 8 digits, with 8 segments. So you'd need 4 of these to light up 28 digits.

2
1

You can buy these displays on eBay for a few dollars. A bit of soldering and you are done (although also pre-assembled ones are available). They can be daisy-chained. Example:

6 x 4-digit 7-segment display modules

You only need 5 wires to the Arduino: Gnd/5V/MOSI/SCK/SCK.

modules in operation

Also, 64-dot displays for displaying arbitrary text:

8x8 LED matrix

Again, only 5 wires.

I have Arduino libraries for driving both sorts of display on Interfacing LED displays with the MAX7219 driver .

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.