So after reading on the internet i figure it out what A,B,C,D,E,F,G,DP does.Also the role of the resistances in series with the 7 segment-diodes(to minimize the current so that the diodes dont burn out).I know that combinations of COM1,COM2,COM3,COM4 give different numbers.
What i don't understand is the role of the transistors and the resistances.Is that a BCD to 7 segment decoder?I guess not because the decoder converts COM1,COM2,COM3,COM4 to 7 segments.
So what does the transistors do?They are there to convert C1,C2,C3,C4 to COM1,COM2,COM3,COM4.But why?How?Please help.


PS:those are pnp transistors.The quality of image is not very good.

 

Its a common Anode led display, they feed the segments (a to g, dp) in the module and illuminate each led, using current limiting resistors.

display

The transistors switch on each Anode separately to enable multiplexing.

 

So wait...i have there 4 digits?Because i have 4 transistors.
I thought that i only have 1 digit with 7 segments.

 

So wait...i have there 4 digits?Because i have 4 transistors.
I thought that i only have 1 digit with 7 segments.

yes four separate displays that have their cathodes tied together, and each has a transistor to drive the Anode.

 

You would think that by just looking at the display you can tell how many digits you have.

 

So inside that LED1 there are 4 digits that have their cathodes tied together and each has a transistor to drive the anode.If com1 is 0(transistor 1 is blocked) then 1st digit doesnt show anything,no matter what A,B to G are(0 or 1).
And each digit has 7 segments.So there are 4*7=28 segments.So there are 28 diodes.

But i have only one set of A,B to G.Aren't these 4 digits all show the same thing together?



On this link:
http://www.thelearningpit.com/lp/doc/7seg/7seg.html
2nd truth table
I thought that SW3,2,1,0 are like my Com4,3,2,1.And different combinations of these give the desired numeral(0 to 9) to appear on the 1 digit.How come there are 4 digits in there?

And further down the page for more than 1 digit they show that by multiplexing u can realize that.But there u have more than 1 set of a,b to g.I only have 1 set.

 

I think you need to start from square one. Give us the model number and link to the display you have.

 

The professor said that the circuit will be designed as an adapter for the development board A1847-V0.And my job is figure out how that scheme works and what does it do.He said also that this is a 4 digit LED display.

The model number is SSAC V0.

The display i have uploaded here(images.jpeg).I dont know if this is the display u're reffering at.(this is from the internet...not from the professor like the other two)