Circuit lab 04 · Beginner · about 30 minutes
Breadboard trainer
A schematic shows what connects to what. A breadboard is where you actually build it, and most first-build problems are breadboard mistakes: two legs in the same strip, a part that does not cross the centre gap, a wire one hole out. Practise here, leg by leg, before you plug in real parts.
How a breadboard is wired inside
Under the plastic, metal clips join groups of holes:
- Columns: in each numbered column, holes a–e are joined, and so are holes f–j. Anything plugged into the same five holes is connected.
- The centre gap separates a–e from f–j. Chips straddle it so each pin gets its own strip.
- Power rails (marked + and −) run the length of the board. Connect the battery to them, then take power from anywhere along them.
On some real boards the power rails are split halfway along. If yours has a break in the red and blue lines, add a short jumper across it.
Try it: hover over (or tap) any hole on the board below. Every hole connected to it lights up, and the panel shows the voltage on that strip, like touching a meter probe to it.
A part only does something when its legs are in different strips. A resistor with both legs in column 7, a–e, is bypassed by the metal clip.
The board
How to build: choose a part, then click a hole for each leg in turn; the prompt above the board says which leg goes next. Press Esc to cancel. A 555 chip is placed by its pin 1 hole, in row f. Click a part to see its readings and change its value. Your layout is saved in this browser automatically.
Model: the same simplified component models as the circuit sandbox (an LED is a fixed forward voltage plus a small resistance; the battery has a small internal resistance; the 555 is a behavioural model). The board’s own contact resistance is ignored. A real build can differ.
The same circuit as a diagram
This is your board drawn as a schematic, updated as you build. Each horizontal line is one connected point (a net): everything in the same strip, or joined by a jumper wire. The battery’s + is at the top and 0 V at the bottom. Hover over a line to light up its holes on the board; click a part to select it.
Drawing rules: lines that cross without a dot are not connected. A part drawn with a loop beside it has both legs on the same net, so it is bypassed. A line ending in an open circle goes nowhere. Chip pins are numbered; unused pins are short stubs.
Breadboard challenges
Each challenge checks what your layout does, so any working arrangement counts. They tick themselves when your board meets the goal. Loading an example unchanged does not count: build it or change it yourself.
This is an example layout as loaded. Change it or build your own to earn challenges.
Check a real build
Built this layout on a real breadboard and it does not work? Measure it with a multimeter and let the model suggest what is wrong.
- Build the layout shown on the board above, part for part and hole for hole.
- Set your meter to DC volts (20 V range on a manual meter). With the circuit powered, measure the battery first, then each part: red probe on the first hole listed, black probe on the second.
- Type in what the meter shows, including any minus sign. Leave a row blank if you did not measure it, then press Check my readings.
How it works: the model predicts each reading (including the effect of a 10 MΩ meter), then tries every likely single fault: each part open, shorted or in backwards, each wire not making contact, a transistor turned round. It ranks the faults whose predicted readings match yours. It can only suggest likely causes: some faults give identical readings, and two faults at once, or a part one hole out, may not be in its list. Readings within about 8% (or 0.15 V) count as matching.
Build with the keyboard
Type hole names: a row letter (a–j) and a column (1–30), such as c12, or a rail: T+5, T-5 (top) and B+5, B-5 (bottom).
Everything on the board
Check your understanding
Next: Project: 555 Blinky, then try it here with the “555 Blinky” example.