Breadboarding: How It Connects, and When It Lies to You

In the main field, each row of five holes is connected together, across the board. The rows are NOT connected to each other. Down the long edges the power rails run the other way — along the board — and are usually marked with a red and a blue line. The channel down the centre separates the left half from the right half. That gap exists so a chip can straddle it with each leg landing in its own private five-hole row; without it, opposite legs would be shorted together. Prove it rather than trusting the description: put the meter on continuity and walk it around one row, then across to the next, then along a rail. Two minutes with the meter replaces any diagram.

On many boards the power rails are broken in the middle — there is a small gap in the printed line where the strip underneath stops and a new one starts. The top half and the bottom half of the same rail are not connected. This produces the most frustrating breadboard fault there is: half the circuit works and the other half is dead, everything looks correct, and the wiring is correct. Bridge the halves with a short jumper at the gap and it comes alive. Check yours with the continuity beeper the first time you use it, and if the rails are split, get into the habit of bridging both rails as the very first thing you do on a new build.

Cut jumpers to length and lay them flat on the board rather than using long pre-made leads that arch over everything. Keep red for the positive rail and black for ground, always. A flat, short layout is not tidiness for its own sake. You can trace it with a finger, you can see which row a wire enters, and you can lift one component without disturbing six others. A bird's nest hides exactly the fault you are looking for. Never push solid wire thicker than about 0.6 mm into a hole, and never push in stranded wire at all. Thick wire permanently stretches the clip, and from then on that hole is an intermittent contact for every circuit you ever build there — the fault that appears and disappears when you touch the board.

Wire the power rails and check the voltage before adding a single component. Then build one functional block, test it, and only then add the next. A circuit built entirely and then powered for the first time gives you one fact — it does not work — and a whole board to search. Built in four stages, the fault is in the stage you just added, which is a search of about five components. This is the cheapest debugging technique in electronics and it costs nothing but the discipline to not wire the whole thing at once. The fault-finding rung that follows is what you do when you did build it all at once anyway.