Four-Bit Adder

Four Bit Adder in Pcbnew

For education and for fun, I put together a design for a four-bit adder demonstration module. It has two 4-bit dip switches at the bottom, with another switch representing the carry-in bit. At the top are five LEDS, representing the four sum bits and the carry-out bit.

The design uses five obsolete quad gate logic chips, with all components being through-hole technology (THT). I'll provide the schematic later after I get this back from OSHPark and confirm that the design works.

Of course, nothing cutting edge here, but I learned a few things in the process. The main lesson was that it is definitely time for me to start working with SMT components. THT just wastes a lot of board space because the traces can't move across component leads on the other side of the board, and so they must try to squeeze in-between components or around the edge of the board, which is wasteful. I was going to try to make my next pcb project using mostly SMT components.

Something new I came across was resistor networks. If you have a bunch of resistors that are all connected on one end to ground, you can use a compact SIP resistor network as an alternative to a bunch of individual resistors. Of course, SIP is still THT, so probably there is a better option.

A three-pack (minimum order) of this board costs about $40 at OSH park. I originally tried to design a similar 8-bit adder, but the board space requirements were crazy and the PCB order would have been far too expensive for my budget.