Hi everyone, just a last note to thank the community for your input. I returned to my local Jaycar (Aussie version of Maplin or Radio Shack), to buy some CMOS chips added a few pull down resistors on the gates and all worked well. After reflecting on this added complexity my students have been missing and the fact that we’re not teaching an engineering lesson, I’ve decided to only do the practical on the half-adder so I can get them used to looking at data sheets and comparing differences between the theoretical world with the real world, and they will complete their 4-bit adder logic design on a simulation only. This will bring a practical component, without being overly complex or risk much failure and frustration. Those particularly adept or interested could continue to a full practical adder as an extension project, but it won’t be part of the standard course for all… a little too early I think.

Anyway, thanks again to you all helping me work through this as a small intro to the subject, I appreciate all your time.

 

I have an idea for an actual practical exercise and an introduction to digital logic gates:
The creation of flip-flops from simple gates.

I created this blog about 10 years ago.

https://forum.allaboutcircuits.com/ubs/flip-flop-fundamentals.705/