# Using seven segment displays with LED bar display drivers

#### FASM

Nov 10, 2015
2
Hello everyone,

I am doing a project for school where I am making a distance measure using an ultrasonic distance sensor, atmega328 with ardunio and LM3914's. For the project I am not allowed to use all programmable circuitry, so I had to come up with alternatives. What I thought of was to use the arduino to find the distance, and output three different pwm signals for each digit of the distance, then run that through a low pass filter then onto a LM3914 so the LM3914 would allow a unique LED to turn on for each number. For example if the distance is 123 cm, LED 1 then 2 then 3 would turn on on three separate bar displays to give you the distance.

I have this working well, however I would now like to display the distance using seven segment displays for ease of use. At first I thought it may be as simple as connecting each output the corresponding segments on the display, but once I tried this all the segments would light up for each number as they were all connected. I have done a fair amount of research and can't find a way to do this without using hundreds of diodes. I have spent quite a lot of time on this project so far so ideally don't want to change the circuit I currently have.

I will upload the schematic of the circuit, just note that as I am new to the software I used I don't know how to add my own IC's, so the picaxe chip represents the LM3914. Also, the LM3914 chip works with LED's of common anode thats why I have put common anode seven seg displays on the schematic.

Any help would be greatly appreciated.

#### dorke

Jun 20, 2015
2,342
What exactly is "all programmable circuitry"?
Is the use of the LM3914 mandatory?
Doing that the way you do is like "scratching your right ear with your left foot"

#### FASM

Nov 10, 2015
2
I mean that I know I could do the whole thing on the arduino, output binary decimals to then go to a binary to decimal converter and display it that way. However, PIC's are only meant to aid other circuitry so I don't want to do that.

The LM3914 isn't mandatory no. Do you have an alternative?

#### dorke

Jun 20, 2015
2,342
The task you want to implement is displaying a result in 3 digits.
There are so many ways to do that.

Let's assume the "direct parallel way" is not allowed.
Assuming 4 bits per digit .

One "simple" way is to use a series signal to "clock" the 12 bits into a shift register.
That means translating from serial to parallel.
Now you can connect directly to 3 bcd to 7-segments drivers and dive the display.
like this IC TLC6C5912 ,if it is not available you can create it with smaller size S.Rs

#### dorke

Jun 20, 2015
2,342
A simpler solution with "serial out data" can be done using this IC
MC14499

#### BobK

Jan 5, 2010
7,682
What an odd task. Sort of like "Build a car with and internal combustion engine, but it must be drawn by a horse".

Bob

Replies
1
Views
77
Replies
1
Views
110
Replies
1
Views
293
Replies
3
Views
306
Replies
8
Views
487