4008B to two seven segment displays


Joined Nov 25, 2009
Of course you can make an 8-bit adder with two 4008 ICs. Just give the carry out of the LSB 4-bit result the the MSB adder.

What I said is that you cannot translate an 8-bit binary to BCD easilly.


Joined Nov 25, 2009
We mentioned the 74185 IC in the first page. The question is if you can get your hands on one. If yes, then it will solve a lot of your problems.

About the cascading of adders, check the last image of this link:

I want you to imagine that each block is one 4-bit adder and that the signals A, B and S are 4-bit vectors. Cin and Cout are still 1-bit signals. Can you see how it can be done?

Thread Starter


Joined Oct 19, 2011
Okay, thank you very much! :D

I'll look into cascading three 74185 chips together to get an 8-bit BCD number :)

Any ideas how I would be able to get this to display on some seven segment displays? I am sorry to keep bothering you and I understand you must be busy

Also, what I am trying to build isn't a calculator however a Base 2 to Base 10 converter. I am tired of having strings of 8-bit binary I have to manually decode.
The switches will each represent a binary value (On for 1, off for 0) and will transcode binary into decimal numbers :)

If I ever get it finished, I'll post some pictures on here :)

Many thanks, Cameron


Joined Nov 25, 2009
Since this circuit is for personal use, you could do some research on the following technique:

Load your 8-bit number in a count-down binary counter. Have the counter share the same clock with a count-up decade counter. Start both counts simultaneously. When you detect 0x000 in the first counter, stop the decade counter. Your binary number should now have been "unloaded" in the decade counter with success. With a medium clock of some kHz that should be done fairly quickly.

Some testing should be done to avoid loosing a stray cycle here and there.