Timers and Comparators

Four lessons. You build a monostable on breadboard and an astable on stripboard.

Lessons

1 · Testing The multimeter, the logic probe and finding faults. 2 · The comparator A thermistor circuit that switches an LED on when it gets hot. 3 · The 555 monostable One press, one timed pulse. Build it on breadboard. 4 · The 555 astable Two LEDs flash in turn. Build it on stripboard.

Practice testing

Learn to Test Nine guided tasks, one for each kind of test. Practise Testing Find the fault on ten boards.

Booklet and slides

Block 6 booklet Tasks and exam questions for all four lessons. PDF. Lesson slides All four lessons. PDF.

Sources & credits: lessons and booklet by R Stewart. The booklet reproduces past-paper questions and figures, each credited in it, © Qualifications Scotland (SQA). R Stewart - October 2026.