2 digit 7-segment display HELP.

[zkjgrty]

Hi all.
I just need some help setting this up.
im using a 2 digit 7 seg display to display temp from a LM35 tem sensor.
The problem is that im using an Atmel Attiny461 micro ( https://www.atmel.com/dyn/resources/prod_documents/2545S.pdf which only has 23 I/O pins. The display im using is a ROHM - LB-602VA2 (18 pins but without disimals im at 14-15)
I know I must use Multiplexing, but the issuse is I have never done it before.
If someone can help me with this it will be highly appricated. If you could state what compnents I need for multiplexing and maybe include a diagram or schematic on how to connect it. Also I am using Bascom to program.
Thankyou

 

[zkjgrty]

Bump :: Anyone help ?

 

[mbarazeen]

you have to program you processor to show both digits one by one and give a status out, ie if its showing 1st digit, one of the free out put has to be configured to hav low, when it displays 2nd digit it will go high.

just route the wiring of the display from the out puts via a digital switch (IC) that will be operated by the status out put (0 or 1) to select required digit.( at a very fast scan rate not to be recognized by human eye)

if you can post a diagram of what you have so far, some one can complete it for you

 

[littletransistor]

In multiplexing, you turn on one digit, and turn off one digit in one specific time, for example 5ms, and the other way round equally in 5ms time as well.

This process is done rapidly and it gives the impression that the both digits are lighted up at the same time.

 

[srikanthsamaga]

Multiplexing uses the property of human eye i.e. persistence of vision.
The trick is that you will operate one display at a time.
The data line for both the displays are shared and some control line is used to select displays.

You need to do this fast so that it appears to be continuously displaying. This is called as refresh rate.
If the refresh rate is low, flickering appears.

 

[davekit]

look at this page to understand more about how a seven segment led works : seven segment displays

 

[colin55]

shree-electronics.com This link does not work.

 

[gelbschnee]

Another problem is that an LM35 is an analog device, you will need to use an ADC before you can get it hooked up to your processor

 

[srikanthsamaga]

shree-electronics.com This link does not work.

Ya I have some problem with the server, It will be functional soon.
Since my site is not for commercial purposes, I had chosen a cheaper service provider, their service is too bad.

 

[srikanthsamaga]

Another problem is that an LM35 is an analog device, you will need to use an ADC before you can get it hooked up to your processor

IMO the AVR processor Attiny461 has ADC built in.

 

[zkjgrty]

This is the kind of setup im thinking of using **broken link removed**, The wires r3,r4,r5 ect are connected to display 1, I would connect wires for display 2 directly to r3,r4,r5 right ? Also I wouldn't be needing a driver IC?
Yes the Attiny461 DOES have ADC convert built in.
Thanks for all your help.

 

[srikanthsamaga]

Connections are proper according to me.
Driver IC is not required.

 

[colin55]

This will not work. You will get "ghosting" via the 4k7 turning on the first display very slightly. What you do to prevent it is this:
Place a 4k7 from the collector of the first transistor to the 0v rail.

 

[zkjgrty]

This will not work. You will get "ghosting" via the 4k7 turning on the first display very slightly. What you do to prevent it is this:
Place a 4k7 from the collector of the first transistor to the 0v rail.

What 0v rail are you talking about? The Gnd on Micro or the First display ?

 

[colin55]

0v rail is commonly called "netative" or "black lead" or ground" or "earth" or "Common," when referring to a simple circuit, or project, or design.
The displays do not have a "ground or 0v" as they are positioned "HIGH" in that they are "pulled high" via the transistors and turned ON via a current limiting resistor to ground.

 

[zkjgrty]

ah, i see what you mean Colin55. To get rid of ghosting can't I use a 2k2 resistor? Another thing is that I will be putting a 5v dc Fan on any left over port, will I be needing more voltage /current to drive both the 2digit display and fan?
Thanks

 

[colin55]

A 2k2 will make the ghosting brighter.
You will need a buffer to drive the fan.

 

[zkjgrty]

I see with the 2k2. Can you elaborate further on this "buffer", im just really new do forgive me.

thankyou

 

[colin55]

You have bitten off more than you can chew, trying to work on a design such as this.
You really should have built 100 projects before venturing into microcontrollers.
A buffer can be simply a common emitter transistor driving a load such as a fan.

 

[zkjgrty]

yes very true have bitten a massive bite. But I only strugel with hardware, programing would be easyer.