3

I would like to have an array of eight 7- and 8-segment LED numerical displays on my Adafruit Trinket. I know that there are some prebuilt arrays of 4 LED's. So 2 in array would do just fine. However, my Adafruit Trinket doesn't have enough ports for that. I have heard something about connecting it to a small piece of controlling hardware that makes me able to have way less ports in need. What is the appropriate way of connecting a lot of those LED's on only a few ports on a micro controller?

My ideal output would be as follow: 88 88:88:88 or maybe 88 88.88.88 So ideally there would be a small space between the first group of 2 digits and the rest. Basically, the last 6 digits will represent a time in minutes, seconds and hundreds of seconds.

4
  • Do you have to use LED's? An LCD with a serial interface would be a better match for that board. You can solve the problem with an I/O expander, but consider simply switching to something built with a full size ATmega328p chip, like one of the mini or micro boards - which would get you both sufficient I/Os and more program resources. May 16 '14 at 14:35
  • The screen should be visible while the sun is blasting on it. That is why I opted for those. Is there even a better solution for outdoor displays? May 16 '14 at 14:39
  • Bright sunlight readability is a tough enough requirement that you should pick your specific display first, and then pick a board to drive it. May 16 '14 at 14:49
  • Do you have a suggestion for a display? I don't have enough knowledge (in fact very little) to be able to pick the correct one. May 16 '14 at 15:01
2

For LED displays, I advise using a MAX7219.

This circuit:

  • can manage up to 8 digits (7-segments + 1 LED for DP or colon separator) or up to 64 LEDs
  • needs only 3 pins to manage display
  • can be daisy-chained if you need to interface with more than 64 LEDs
  • requires only 1 resistor to be fully functional
  • is easily supported on Arduino with this library

I have used it in several circuits and happy with it.

Note that there also other libraries that support this circuit but I haven't used them.

This circuit has only one downside: its price (about $10 each); but the price is counter-balanced by its simplicity and the fact you don't need any additional component (e.g. transistors) besides a simple resistor.

1
  • Wow thanks for this answer! I will look into it this weekend. Looks perfect for what I need! May 16 '14 at 23:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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