# 7 segment display total confusion

Discussion in 'General Electronics Chat' started by RodneyB, Dec 19, 2012.

1. ### RodneyB Thread Starter Active Member

Apr 28, 2012
652
14
I am trying to make a novilty number to be displayed on our post box. I have a dual seven segment display KingbrightDA56-11EWA. Common Anode right hand decimal.

As I wanted to be able to display severalnumbers I am trying to drive the 7 segmentdisplay with a SN74LS47N Which is A BCD 7 Segment display driver Yje Datasheet shows a maximum 15 Volts. Is that the maximum supply voltage for the IC.

I Have Pins 4 & 5 B1/RB0, RB1 ( both on data sheet have lines shownabove them and I have no idea what that means or how to show it here. ) connected to the positive.
Pin 3 LT (Again with a line able it ) can be switched to goto the positive
Pins 1,2 6,7 B,C,D,A Can be switched on to the positive or off .
The pins to the 7 segment display are connected through a 150R resistor. The common on the Display is connected to the +ve.
I have connected a 5 Volt supply andnothing happens.
I have removed the IC and Taken a jumper from the Negative through each resistor and each segment lights up. But Icant get it to work from the IC and nervous to increase the voltage from 5 volts,I cant seemto findthe correct supply voltage.
Assistance willbe appreciated.
Thanks
Rodney

2. ### crutschow Expert

Mar 14, 2008
13,505
3,376
It's rather difficult to follow your circuit description. Can you post a circuit diagram?

3. ### MrChips Moderator

Oct 2, 2009
12,636
3,455
Do not increase the voltage above 5V.
Post a circuit diagram.
Post a photograph of your wiring.

Did you connect pin 8 to GND and pin 16 to +5V?

Temporarily connect pin 3 (Lamp Test) to GND and you should see all segments light up to display 8.

You cannot simply connect switches from +5V to A, B, C, D inputs because TTL inputs will float high.
You can either use 100 - 220Ω pull-down resistors or a better solution is to put the switch to GND and use 1k - 4.7kΩ pull-up resistors.

How many digits do you need and what number do you want to display?

Last edited: Dec 19, 2012
4. ### RodneyB Thread Starter Active Member

Apr 28, 2012
652
14
I will post a diagram of the project thanking you in advance

5. ### RodneyB Thread Starter Active Member

Apr 28, 2012
652
14
Please see the drawing as requested

File size:
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6. ### MrChips Moderator

Oct 2, 2009
12,636
3,455
The LED shows CC on pin 6. I presume you meant CA as in common-anode.

Don't wire the switched to +5V. Wire the switches to GND (pin 8 of 74LS47)

and close the LT switch at pin 3 (to GND) and tell me what you get.

7. ### RodneyB Thread Starter Active Member

Apr 28, 2012
652
14
I connected all the switches to the negative .

Pins 4 & 5 connected To the Positive

Pin 3 connected to the negative and switched on and all the segments come on showing the figure 8.

Pin 3 switch off all segments off

Then its strange what happens next

according to the data sheet

B= L
C=L
D=H
A=H

shouldgive the digit 3

Howeverit displays a 6

I went through allthe combinations shown on the data sheet and nothing corresponds.

I connected pins 4 & 5 to the negative and nothing came on. Conected them backtothe positive Lamptest works and Still get 6

Thanks

Rod

8. ### absf Senior Member

Dec 29, 2010
1,493
374
D_C_B_A = "HLLH" = 1001 bin =9 dec

Could it be 9 instead of 6?

Allen

9. ### RodneyB Thread Starter Active Member

Apr 28, 2012
652
14
I wish the decimalpoint is at the bottom right.and no other numbers come out

10. ### RodneyB Thread Starter Active Member

Apr 28, 2012
652
14
Many thanks for all the help I had a join between 2 tracks and I was making a mistake reading the data sheet forthe numbers. I just want one last piece of advice! I want to add some spark to this so want to add some routine to the display using a PIC12F675. If the Pins on the pic are low, will the 7 segment displaystill light up with out damaging the PIC. I want to Run the routine on the pic, lighting segments on the display and eventually counting down tothe desirednumber.