# Multiplexing 7 segment displays

#### Overclocked2300

Joined Apr 24, 2005
124
How would I connect more than one 7 segment display or more than 1 7447 decoder?

Example: One led display would represent the 10's column and the other would represent the 1's

I want to convert a voltage to digital. I want it to display that voltage on a 7 segment display. The A/D converter is 8 bits.

and ignore those LEDs

#### beenthere

Joined Apr 20, 2004
15,819
Hi,

There's more to the display yet. Your 7 segment displays will only show 0 - 9, so you are going to have to translate the A to D output into decimal. Eight bits is 0 - 255, so you'll need three 7 segment displays and decoder/drivers, plus logic to convert from binary to BCD.

#### thingmaker3

Joined May 16, 2005
5,083
If you want to control more than one display with a single 7447, then you will need to multiplex its input and demultiplex its output. It would be far easier to use mutliple 7447s.

Converting Binary to 3 digits BCD will need either a PROM or a PIC. (Or more gates than sanity permits...)

#### Overclocked2300

Joined Apr 24, 2005
124
But for what Im using it for I only need 2 digits.

I was just going to match up the outputs of the A/D converter to the inputs of the 7447 and match lsb and msb.

#### thingmaker3

Joined May 16, 2005
5,083
Originally posted by Overclocked2300@Jun 12 2005, 06:49 AM
But for what Im using it for I only need 2 digits.

I was just going to match up the outputs of the A/D converter to the inputs of the 7447 and match lsb and msb.
[post=8449]Quoted post[/post]​
What you plan on will give you a decimal value between 0 and 15, inclusive. Without resorting to a PIC or PROM or shift register or such, you will need to do the following:

1) Determine if the ADC output is less than ten or more than nine. One way to do this would be with two AND and one OR gates. If (Bit8 AND Bit4) OR (Bit8 AND Bit2) then (two digits) else (one digit).

2) For values of 10 through 15, you will light up a "1" on the left hand LED array. There should be no need for a driver chip, since the left hand array will never be anything other than "1" or blank.

3) Also, for those same values of 10 through 15, you will need to subrtract ten from the input to your 7447. But you do NOT do this for values of zero through nine.

Remember: If the value 16(decimal) or higher comes out of the ADC, then your displayed numbers will be wrong.