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[on:]

Hi, I'm working on a student project, which has multiple probes (temperature and power) and I want to show the readouts of them on an LED display. I originally was planning to use a microcontroller for each probe/LED combo to tell the LEDs how to light up. But I was wondering if I could use a single Arduino board instead of multiple microcontrollers?

[Reply #1 on:]

It is easier and cheaper to use an LCD display rather than an LED display. With LEDs you need to multiplex them and generate an image. With LCD displays you just throw ASCII code at it and it stays there displaying what you put.

[Reply #2 on:]

Thanks for the input! As for the LCD/LED bit, I unfortunately already picked up some LED drivers. Would the greater ease of using the LCDs justify returning the the LEDs I picked up and getting the LCDs instead?

[Reply #3 on:]

I was going to use the MAX6951 Serially Interfaced, 5- and 8-Digit LED Display Drivers.

http://www.maxim-ic.com/datasheet/index.mvp/id/3195/t/al


Also, I was looking at the Arduino Uno or Nano to use. It looks like they're mostly the same, except the Uno has more memory/RAM, but the Nano is more compact if space is an issue. How accurate is that?

[Reply #4 on:]

The MAX6951 is a nice chip, can drive eight 7-segment displays, best if you can supply it with 3.3V instead of 5. Mine got really flaky after a few hours at 5V, then was even worse the next morning.
Also be aware it is only available in a little teeny tiny surface mount package, about half the size of  your pinky fingernail, with pins that are 4 times as dense as a regular DIP thru-hole package (pins are 0.025" apart vs 0.1"). I had mine on a surface mount to DIP adapter so I could plug it into a regular breadboard.
I would encourage the slightly larger MAX7221 in a regular DIP package instead. Also much easier to keep the wiring figured out with its more traditional multiplexing (vs charlieplexing).
All your segments (A-G plus DP if used) are wired in parallel, then you just have the one cathode wire to go seperately to each display.

http://www.maxim-ic.com/datasheet/index.mvp/id/1339

[Reply #5 on:]

The 7221 uses multiplexing whereas the 6951 uses charlieplexing? I'm afraid I don't have much experience with charliplexing; is it much trickier than multiplexing?

Also, I had a major brainfart, and was focusing so much on the drivers, that I didn't actually get a display, LED or LCD.

[Reply #6 on:]

The 7221 uses multiplexing whereas the 6951 uses charlieplexing?

Yes. The 6951 makes it less complex, but the part itself is hard to work with due to its physical size, tightly spaced pins, and only wanting to really drive 3.3V. I think it is intended for small displays.
The 7221 is much friendlier to work with physically.
For example, compare this to the MAX7221 post;
You save 7-8 wires, but effort involved in doing that is high unless you have a PCB readily available to put the max6951 on to, or a DIP adapter like something from Logical Systems
http://www.logicalsys.com/painfo-vpasp-vb.asp?adapter=pa-qsd3sm18-16
This doesn't provide a pad for the bottom of the max6951, so cooling might have been part of my problem. Soldering it onto the adapter was a challenge.

If you don't have a display yet, I guess you still  have options to consider :-)