Seven segment display acting wierd.

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Discussion Overview

The discussion revolves around issues encountered with a seven-segment display, specifically the differences between common cathode and common anode types, and the resulting behavior when using a CD4543 decoder with an LD5161 display. Participants explore the implications of these differences on circuit design and functionality.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes experiencing erratic behavior with a common anode seven-segment display when using a CD4543 decoder, noting that the display responds unexpectedly to movement near the power supply.
  • Another participant emphasizes that common cathode and common anode displays require different circuit methods and warns against mixing them in the same circuit.
  • It is stated that the CD4543 is designed to work with common cathode displays, where a high output turns on a segment, while a common anode display would require inverted signals to function correctly.
  • A later reply confirms that the CD4543 is indeed for common cathode displays, but another participant claims to have tested it with a common anode display and found that inverting the signals did not work, leading to a different segment lighting issue.
  • Participants discuss the LD5161 display, with one asking for more information about it, indicating a lack of familiarity and resources available online.

Areas of Agreement / Disagreement

Participants generally agree on the necessity of using the correct type of display with the CD4543 decoder, but there is disagreement regarding the functionality of the CD4543 with a common anode display, as one participant claims it does not work as expected even with signal inversion.

Contextual Notes

There are unresolved questions about the specific behavior of the LD5161 display and its compatibility with the CD4543 decoder, as well as the exact wiring needed for different display types. Some assumptions about circuit connections and component behavior remain unverified.

Who May Find This Useful

Electronics enthusiasts, students working on display circuits, and individuals troubleshooting similar issues with seven-segment displays and decoders.

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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