Binary to Seven Segment Display

Thread Starter


Joined Oct 5, 2021
I made a simple 8-bit adder using npn transistors for logic, an adapter for making the 230 V from the power outlet to 12 V, and some resistors to adjust the circuit electric needs. I have 16 buttons(8 to input 1 number, 8 for 2nd number). The transistors process this numbers and sum them and I output the sum to 8 leds. I want to output the result in decimal system and I found this 7 segment displays. The problem is that I need to think how to light the seven segments to draw digits based on the 8 binary digits represented by on/off leds. Is there any 7 segment display that take 8 inputs(binary digits) and do the computation needed to light the 7 segments, because I think I can't find the logic to convert the binary to digit segments:
0000 - ABCDEFG
0001 - ABCDEFG
0010 - ABCDEFG
0011 - ABCDEFG
0100 - ABCDEFG

I found a tutorial that explains how to do that, however I am not that advanced and I can't understand it yet, so I need a electronic circuit that does the conversion on numbers for me.


Joined Mar 30, 2015
Welcome to AAC!

What you want is a binary to BCD converter. National Semiconductor, and others, used to make a chip called 74185. Three chips could do an 8 bit binary to BCD conversion:

Those ICs are now unobtainable. You could replicate using 32x8 PROMs, which is what the manufacturers did. Or you could use a 16 bit wide EPROM. I programmed one that would do 4 BCD digits.

You can do it with gates, but it would take several dozen gates. I've simulated it, but never breadboarded one.

Another option would be to display the results in hex. They used to sell binary to hex decoders, but those also seem to be difficult to obtain.

Thread Starter


Joined Oct 5, 2021
Thank you! It is impossible for me to make it with logic gates because I am not using breadboards or logic chips like and/or mini chips, I made them using transistors. For example I made ands using this diagram:
They are quite large, for example and is about 10 cm2 so the adder is as large as my entire living room, so to create the logic to convert the binary would mean to expand the adder to neighbour's yard. So I'll try to find the circuit you mentioned.


Joined Mar 14, 2008
There is no simple combinational logic to go from 8-bit binary to BCD.

One way to convert binary to BCD is to use a binary down-counter coupled to a BCD up-counter.
The binary counter counts down to zero from the binary input value, which the BCD counter counts up from zero at the same time.
When the binary count reaches 0, the BCD counter contains the binary value in BCD.
This is further discussed here.
To display the 255 maximum of the 8-bits would require two binary counters and three BCD counters.
To go directly to the BCD display, you could use a BCD counter with 7-segment output such as the CD4026.
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Joined Mar 30, 2015
It is impossible for me to make it with logic gates because I am not using breadboards or logic chips like and/or mini chips
If learning how to do the converter isn't one of your learning objectives, is using something like an Arduino Uno a possibility?


Joined Feb 24, 2006
I don't see that you have very many viable options. Allegedly the APG (Apollo Guidance Computer) was constructed from RTL (Resistor Transistor Logic) 3-Input NOR Gates. I'm quite sure your problem can be solved in a similar fashion. You just have to work out the details.