Archive for the ‘Send Your Problem’ Category


Interview Question – BCD Digit, Multiplied by 5

December 21, 2008

A while back, someone sent me the interview question I am about to describe, asking for help. I think it serves a very good example of observing patterns and not rushing into conclusions.
I will immediately post the answer after describing the problem. However, I urge you to try and solve it on your own and see what you came up with. On we go with the question…

Design a circuit with minimum logic that receives a single digit, coded BCD (4 wires) and as an output gives you the result multiplied by 5 – also BCD coded (8 wires).

So, I hope you got a solution ready at hand and you didn’t cheat 😉 .

Let’s first make some order and present the input and required outputs in a table (always a good habit).

Looking for some patterns we can see that we actually don’t need any logic at all to solve this problem!!

You will be amazed how many people get stuck with a certain solution and believe it is the minimal one. Especially when the outcome is one or two single gates. When you tell them it can be done with less, they will easily find the solution. IMHO there is nothing really clever or sophisticated about this problem, but it demonstrates beautifully how it is sometimes hard for us to escape our initial ideas and approaches about a problem.

Coming to think of it, this post was more about psychology and problem solving than digital design – please forgive…


Send Your Problem

November 13, 2007

Being the generous person that I am 🙂 I decided to open a new section in this blog called “Send Your Problem” or SYP.

If you have a design problem of any sort, that you think would interest others, or just that you need help with – send it over – yes, you heard it right. I will try to do the best I can to pick up the most difficult/interesting problems and post them with some solutions (hopefully).

I have limited time, and I really do it on my own spare time so be patient if it takes me time to answer. I will of course, try to address all questions, at least by email.