# 7-segment display decoder

truth table for a 7-segment display decoder. It converts a binary input x[3..0] to a 7-bit code which drives each LED in an LED display am a bit confused can anyone just give a hint i want to produce a logic circuit for it i take it up from there cheers .

• What are you confused about? The table seems clear enough.
– JRE
Commented Jul 24, 2015 at 15:27
• @JRE he didnt get that he need to do 1 karnaugh map per output. Commented Jul 24, 2015 at 15:31
• Is this just for fun, or for a larger project? You can get decoder chips for about 50 cents. Commented Jul 24, 2015 at 15:55
• its just for fun @whatisname Commented Jul 24, 2015 at 15:57
• FYI, I'd call this an "encoder", not a "decoder". To me, a 7-segment decoder would take the 7 signals being fed to a display and turn it back into a 4-bit value. Commented Jul 24, 2015 at 18:47

You can do a Karnaugh map for each output, as has been suggested, however you should then see if there are any common terms that can be used to simplify the logic.

Check out the logic diagrams of common 7-segmend decoder/drivers such as the 7447, CD4511.

• In the top schematic the AND gates connected to NOR look like minterms with some fancy way of producing the X and /X inputs incorporating the lamp-test and blanking inputs. But how do you get the setup with only NOR gates (I figured the NAND gates just turn of the LEDS for 11-15) as in the second schematic? What's that called or is that something someone came up manually? Commented Aug 28, 2016 at 0:12
• NOR+NOR is equivalent to AND+OR with inverted inputs and inverted outputs. Commented Aug 28, 2016 at 1:18

If you are doing it by "hand". You need to make a Karnaugh map for each segment and after that you will end up with SOP or POS that can be implement into logic gate circuit.

So the final circuit is made of 7 smaller circuit that link each segment to the input of the circuit.

The way to do this by hand is by drawing a K-Map. You will draw a table for each of the 8-outputs and find the Boolean expression by the help of which you can draw the digital circuit for each of the output separately.

If you are not familiar with the concept of K-Maps, then go through this