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Odd double digit display

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thatdecade

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.
 

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
}
 

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.
 

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.
 
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thatdecade

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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