Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

2 digit 7 segment display

Status
Not open for further replies.

soryo

New Member
Seeking help.

Im currently doing a project relating to microcontroller, temperature sensor and a whole lot of small stuff to make a big bunch of stuff.

To cut things short, im doing the 2 digit 7 segment display.
I manage to get single digit 7 segment to lit up but not 2 digit together. I start to doubt 2x7447 could not make up 2 digit 7 segment. If it is possible could someone care to show me how it could be done?

Here is the current schematic i made up but it is still 2 individual 7 segment instead of 2 digits.

**anyway, i forget the connection from the 7447's GND to GN
 

Attachments

  • drawn schematic00.jpg
    drawn schematic00.jpg
    59.9 KB · Views: 2,630
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
Why not drive the displays from the micro-controller? - it seems a complete waste of two extra chips?.

Check my PIC tutorials for an example of how to do it with a PIC.
 

soryo

New Member
Well, using microcontroller to run it require 14 input port to the 2 digit 7 segmet and plus 1 more for LED to indicate polarity.

Using transistor will make it less. True.

Since im already done the 7 segment and troubleshooting it. I thought i could continue. Then i will not need to do so much programming on my limited space microcontroller.

Im using AT89S52 (only contain 8Kb Programmable Flash Memory). I still have programs for other part of my system.

Back to 7 segment. Is there any combination of logic that will make the thwo 7447 to form a 2 digit decoder?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
soryo said:
Well, using microcontroller to run it require 14 input port to the 2 digit 7 segmet and plus 1 more for LED to indicate polarity.

Using transistor will make it less. True.

No, you only need eight connections in total to the two LED's, plus an extra for your polarity indication - it's called multiplexing, and is almost universal with LED displays.

There's also a more complicated version called 'charlie-plexing' which uses even less wires.
 

soryo

New Member
https://esd.cs.ucr.edu/labs/mdec_counter/mdec_counter.html

this is one example link and resource i found. But i have no knowledge on those and it is a counter instead of a normal 7 segment display. Instead i go for something i know but it doesnt work as i want it to be =(

I have 12-bits output to my microcontroller that will be feed into my 7 segment ( 8/12 -bit )

Someone can give me a head start on using multiplexer?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
soryo said:
https://esd.cs.ucr.edu/labs/mdec_counter/mdec_counter.html

this is one example link and resource i found. But i have no knowledge on those and it is a counter instead of a normal 7 segment display. Instead i go for something i know but it doesnt work as i want it to be =(

That's the sort of thing, except as it only uses two digits, you can use a single pin to select between them, saving an extra pin - like this .

Being a counter makes no difference, it's the hardware you're looking for, and just take the pieces of sofware you need, or write your own from scratch?.

I have 12-bits output to my microcontroller that will be feed into my 7 segment ( 8/12 -bit )

Well 12 bits gives four digits resolution (0-4095), so how do you want to display it on two digits (0-99)? - basically you're probably looking at maths routines.

Someone can give me a head start on using multiplexer?

Although you can't use the PIC code, will give you an idea of how multiplexing works.
 

soryo

New Member
Nigel Goodwin said:
That's the sort of thing, except as it only uses two digits, you can use a single pin to select between them, saving an extra pin - like this .

Being a counter makes no difference, it's the hardware you're looking for, and just take the pieces of sofware you need, or write your own from scratch?.

will look into it. Thx nigel

Nigel Goodwin said:
Well 12 bits gives four digits resolution (0-4095), so how do you want to display it on two digits (0-99)? - basically you're probably looking at maths routines.

the output is from a digital thermometer that has fix address for certain range of temperature. Those are fixed addresses that cannot be altered, therefore the output is at a 12-bit resolution.

Unless i convert the 12-bit to a 8-bit resolution, which is very hard in term of programming a decoder for it in the microcontroller. But i shall see what i can do 1st.
The 12-bit digital thermometer read from a range of +125 Degree C to -55 degree C. Between the polarity(+ve, 0, -ve), the MSB is the indicator of the polarity. Even though it is a 12-bit, it do not make use of every bit and address

Nigel Goodwin said:
Although you can't use the PIC code, will give you an idea of how multiplexing works.

will look into it more in detail. thx
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
soryo said:
Unless i convert the 12-bit to a 8-bit resolution, which is very hard in term of programming a decoder for it in the microcontroller.

It's dead simple - just use the top 8 bits, and discard the bottom 4 bits (VERY simple divide by 16).

However, that probably isn't what you want? - you will probably need to scale (multiply and/or divide) the 12 bit number to get the temperature readings you want.
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
ThermalRunaway said:
You beat me to it with the multiplexing idea Nigel, but I've never actually heard of Charlie-Plexing... :rolleyes:

You've not been paying attention!!!.

Expect 'Mike, K8LH' to pop up any moment, he's posted LOT'S of charlie-plexing projects on these forums!.

You might also check https://en.wikipedia.org/wiki/Charlieplexing - interesting where the name came from!.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top