Driving a 3 digit 7 segment display with as small of a footprint as possible.

I was driving a 3 digit 7 segment display directly from the I/O pins of ATmega328 just to mess around. I'd like to use a driver if possible now, but all the drivers I see when searching have huge footprints with many pins that aren't going to be used.

Which one would you recommend? I tried searching digikey and filtering results etc. Maybe I'm not filtering them correctly. The MAX7219 seems the closest to what I'm looking for, but I don't need 8 digits.

Hi,

I'm not surprised, max7219 is pretty much the most convenient out there, even for 3 digits.

Is your display common anode or common cathode? If common anode, you could look at tpic6c595.

Paul

Hey, just get one of these and ignore (or in fact use the extra digit). :grinning:

Of course, the only thing about using a MAX7219 with three digits instead of eight, is that the digits are twice as bright (since you are multiplexing by three instead of eight. You actually have to reduce the driving current)!

This is going on a custom PCB and needs to be as small as possible. I'm using a 0.28" 3 digit 7 segment display. I think driving the display directly from the I/O pins might be the way to go after all for this project.

My other issue is I was hoping to use a linear regulator and go from 12v to 5v, so power dissipation could be an issue.

I'll keep reading up.

noobdude:
I think driving the display directly from the I/O pins might be the way to go after all for this project.

You are using some transistors to drive the common pins, aren't you? Otherwise you could easily overload the Arduino pins connected to them, unless you have high value series resistors (e.g. 1K).

noobdude:
My other issue is I was hoping to use a linear regulator and go from 12v to 5v, so power dissipation could be an issue.

Depends what else the circuit is doing, but if the led display is the only major current requirement, I don't think dissipation will be a problem. Even if your segments draw 20mA each, that's still only 160mA in total (because only 1 digit at a time is lit). Most regulators will handle that, unless you pick a really tiny one like 78L05.

Paul

Yeah, I'm using transistors for the common pins. I limited the current to around 10ma per segment and I remember after I calculated it there could still be an issue. I might have to use a buck converter to power the board. This would actually be nice, since I could use much higher input voltage than 12v.

I even tried only lighting one segment at a time, but it looks very odd. I might try lowering the current to each segment a bit more.