Build and analyse a simple clap switch circuit available as a kit
Here’s a quick video of the kit in action:
Here’s a simple circuit that’s available as a cheap kit - “shopping-cart stuffing”. There are no unusual components so aside from the PCB, everything you need is probably already in your parts bins.
The core of the circuit is a set-reset flip flop implemented with BJTs - similar to the RSFlipFlop project.
A momentary pulse from the electret is amplified with Q1/Q2 and triggers the Q3/Q3 flip:
- the cap C5/C6 on the side of the flip-flop that is “off” will charge momentarily
- when Q2 shuts-off, the charged cap voltage offset will reverse-bias the corresponding D1/D2
- causing the corresponding BJT to be enabled and trigger the flip/flop
The output LEDs are driven with a push/pull configuration of Q6 and Q7. Q6 and Q7 are driven with complementary base “inputs” (Q5 prividing the inverted signal for Q7).
So when the right-hand output of the flip-flip (tapped at the Q4 collector) is “low”:
- Q6 will be on (D3 conducting via Q4)
- Q7 is off (Q5 base pulled low via D4/R12/Q4)
- therefore LED1 (green) off, and LED2 (red) on
And when the right-hand output of the flip-flip is “high”:
- Q6 will be off (D3 reverse biased)
- Q7 on (D4 reverse biased, so Q7 based pulled high by R13)
- therefore LED1 (green) on, and LED2 (red) off