Using seven segment displays with LED bar display drivers

[FASM]

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]

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]

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]

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]

A simpler solution with "serial out data" can be done using this IC
MC14499

 

[BobK]

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

Bob