Seven segment display acting wierd.

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The discussion centers around issues faced when using a seven-segment display, specifically the confusion between common cathode and common anode types. The user initially experienced erratic behavior with a common anode display while using a CD4543 decoder designed for common cathode displays. It was clarified that the CD4543 requires a common cathode configuration, as it outputs high signals to turn segments on. The user later confirmed that the CD4543 indeed drives common cathode displays, leading to further troubleshooting of the circuit. There is also a query about the LD5161BG component, which remains unresolved as no information was found.
kElect
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Ok for class, I had this 7segment display(common cathode) and it worked great. Then I bought more, but I bought the common anode kind. And this time, it doesn't work so well. For some reason the numbers change when i wave my hand over the power supply; I am not even touching it. I'm using cd4543 decoder with the ld5161.

..wait i just tried again, and nothing happens but when i pick up the power supply all the segments turn on even though the switch is on 0000 wtf...

can someone tell me why my seven segment display does weird things when i mess with the batteries?
 
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Common cathode and common anode will need different circuit methods to drive them
I would hope you are not trying to mix them or use the same circuit to drive one or the other ??

Dave
 
The 4543 has to be used with a common cathode display.

To turn a segment on, you make that output high.

If you connected a common anode display in circuit, the LEDs would only turn on if the anode was connected to the positive supply, but then a high drive signal would turn the LED segment off and a low signal would turn it on.

So, you would have to invert every drive signal.

Try to get a common cathode display.
 
vk6kro said:
The 4543 has to be used with a common cathode display.

To turn a segment on, you make that output high.

If you connected a common anode display in circuit, the LEDs would only turn on if the anode was connected to the positive supply, but then a high drive signal would turn the LED segment off and a low signal would turn it on.

So, you would have to invert every drive signal.

Try to get a common cathode display.

nope. 4543 is common anode. just tested inverting everything, the light doesn't turn on at all. it stopped blinking though. i think before the resistors were touching so it was acting weird. it still doesn't work though. it stays lighted on the middle segment only now, all others don't turn on and nothing changes when i flip the switches.

is anyone familiar with the ld5161bg? i bought this on ebay.

edit: nvm ur right. the truth table looks like it is common cathode.
 
Last edited:
According to the data sheet, it drives common cathode displays. This is shown by the outputs being high for lighted segments.

You connect them like this:
http://park8817.com.ne.kr/COMMON_CATHODE_CIRCUIT.jpg

To make it work with a common anode display, you would have to connect it like this:

images?q=tbn:ANd9GcQYlXuyzbBVZbv7UQCRS-cqYe_59eIAkn6d7AN0h4C7nFcQx9Bh9Q.png
 
Last edited by a moderator:
kElect said:
is anyone familiar with the ld5161bg? i bought this on ebay.

never heard of it and nothing on google... what is it an IC ? a display?
have you got the ebay link ?

Dave
 

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