# Odd double digit display

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##### New Member
7 Segment Double Digit Blue 1.0 Inch (25.4mm) LED Display Specs, Data Sheet LCD-10022TB11 from lc-led.com

I bought a few of these 2 digit 7 segment displays and after wiring one up, I am not sure what purpose the manufacturer intended.

Take a close look at the circuit drawing on that page. 10 pins. 1 common pin for each side. The rest of the pins, abcedfg, are shared between the sides. If I power both common pins and light up segment A, segment A for both digits will illuminate.

I had intended using it for a timer/counter. That is out, so now I am trying to think of a good use of this strange display.

#### hdc090360

##### Member
It is designed to be multiplexed. It is a good display for driving off a microcontroller.

#### Burningmace

##### New Member
You use a microcontroller to multiplex the display. For example, if RA0 and RA1 are linked to transistors on the common pins and RB0 to RB7 are connected to the 7-seg pins, you could do something like this:

Code:
int HexDisplay[] = { ... } // insert values for displaying 0 -> 9
int countA = 0;
int countB = 0;
while(true) {
clear(RA1);
set(RA0);
RB = HexDisplay[countA];
clear(RA0);
set(RA1);
RB = HexDisplay[countB];
// check WDT here and increment countA/countB appropriately
}

##### New Member
That makes a lot of sense. Not what I expected, but saving on IO pins and battery life is a huge plus. Thanks.

#### blueroomelectronics

##### Well-Known Member
If battery life is important then 1" LED displays are not known for being battery friendly. LCD displays are very battery friendly.

##### New Member
lol, I see your point. The end use is for a prop. Requires a illuminated display with blue characters.

#### Burningmace

##### New Member
When you multiplex them with a PIC you're only actually lighting one LED at a time. Since the switching is extremely fast (I'd guess ~1MHz on a 4MHz clock) you can't tell that they're flickering on and off. You're not likely to be consuming more than 70mA for the LEDs and PIC when multiplexing.

Last edited:

##### New Member
70mA... hmm I may have to sacrifice an IC to test out a theory. If I ditched the transistors and connected the two common pins directly to the IC, that would mean at most there would be a 35mA load. My IC can support max loads of 40mA per pin.

Reducing the components is worth a \$2 risk on the prototype. ha~!

#### Burningmace

##### New Member
You should be ok, but 70mA was a ballpark figure so don't be dissapointed if it does kill the chip. It could be more, it could be less.

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