I have made this circuit on Proteus, a simple BCD to 7-segment display:
But the segments for 6 and 9 are not completely lit. What could be the potential reasons? The decoder IC is CD4511 and a common cathode display.
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4 Answers
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The CD4511 decoder is working as intended, see page 4 of its datasheet shown below:
There are decoder-drivers like the MC14495 that have tails on the outputs but these are eye-wateringly expensive since they are vintage parts from back when.
You could possibly use something like a 4056 with a buffer to overcome its sub-mA current source limit. A latch would allow you to multiplex multiple displays off of a single 4056.
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As Vir mentioned, the chip is working as designed. But you can get the desired results your looking for with additional logic. Thy this:
simulate this circuit – Schematic created using CircuitLab
Keel all the other connections the same. The caveat is you might lose some of the "fancy" features of the decoder. Or maybe not; I don't have time to check. Try running the simulation. If so, you can correct the situation with additional logic.
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1\$\begingroup\$ You don't need to look at A for the d-segment logic. That AND gate isn't needed. \$\endgroup\$periblepsis– periblepsis2025-11-08 04:33:40 +00:00Commented Nov 8 at 4:33
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\$\begingroup\$ @periblepsis but it comes for free in the dual package :-). But all jokes aside, you're probably right; I didn't look too far into it. I was mostly alluding to the fact that you can tailor the aestetics of the display with glue logic. \$\endgroup\$MOSFET– MOSFET2025-11-08 05:29:14 +00:00Commented Nov 8 at 5:29
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3\$\begingroup\$ Yeah. I get that. I just noted that 8 and 9 (under the OP's desire, anyway) both want d-segment. So there's no need to check for 9, exactly. Just knowing it is 8 or more is enough. Saves a gate. That's all. Brain just always goes there because back in the 1970's I wired-wrapped up 30+ boards to make a computer from 7400 series logic and every darned gate meant pain and suffering to me. The resulting PTSD (hehe) from that year+ of time has made me spot unneeded gates as if my life depends on it. ;) It kind-of did, back then. People have it easy, now. \$\endgroup\$periblepsis– periblepsis2025-11-08 05:32:26 +00:00Commented Nov 8 at 5:32
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This is quite normal and matches the behavior of 7447 etc, as well.
If you need a real part that does the decoding function and provides “tails” on the 6 and 9 you could consider the 74HC247, which lcsc has in stock for small quantities, albeit from a less-known source. The LS version was more widely available. Those parts are designed to work with common-anode displays.
It’s far more usual these days to use an MCU to provide a decoded output, allowing complete freedom as to which segments are illuminated (for example you could decode to hex characters where the b is like the 6 in your decoder- or a pattern representing a symbol such as the degrees symbol). Just a few lines of code.
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This is a US-American/British way to write this numbers.
The Datasheet gives you a representation of this encoding. In Europe and other parts of the world the people are using simply a bit different way of writing.
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\$\begingroup\$ No this is not the British way of writing a 6 or a 9. I must add that the character 6 (as depicted in the question) can be mistaken for the "b" character in old hexadecimal calculators and, it was thoroughly explained in their manuals not to get confused between the two. So no, this is not a brit way of showing 6 but, that's just my personal opinion based on past experience. \$\endgroup\$Andy aka– Andy aka2025-11-08 01:14:58 +00:00Commented Nov 8 at 1:14
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1\$\begingroup\$ I have seen this from British and American people in their videos. We write the 1 like /| and they write only a "|" like the Chinese do it too. With the 9 and 6 the same, they write it like a b and a inverted b. We write the 7 with a short horizontal line in the middle, they don't. And I did see this type of encoding in old American calculators. \$\endgroup\$MikroPower– MikroPower2025-11-08 04:05:17 +00:00Commented Nov 8 at 4:05
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5\$\begingroup\$ I believe this is more a matter of personal preference than a US/UK difference. I've seen both used by people from both countries. \$\endgroup\$Hearth– Hearth2025-11-08 04:55:37 +00:00Commented Nov 8 at 4:55
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3\$\begingroup\$ I suspect that those who work in engineering and in software particularly tend to use disambiguating marks from any source available. A dash through a 7, a diagonal or horizontal line through a zero and a tick at the top of a 1 so it doesn’t look like a lower case l or upper case I, to name a few. I wonder if the choice of font in the 4511 was made to save a few mA. \$\endgroup\$Frog– Frog2025-11-08 09:51:28 +00:00Commented Nov 8 at 9:51
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1\$\begingroup\$ @Spehro'speff'Pefhany in the UK, this (4 open or closed) seems to be a matter of personal style, but a crossbar on a 7 is seen as (continental) European - even though I do it myself \$\endgroup\$Chris H– Chris H2025-11-10 09:37:14 +00:00Commented Nov 10 at 9:37
6looks likeband9looks likeq. If only one of these was the case and the user knew, then9and6wouldn't get confused even when they're upside down. That might be the origin of this font. Or saving energy. \$\endgroup\$