This is a simple flashing led circuit with 2 leds and 2 NPN transistors. It illustrates the behavior of transistors and capacitors and if you use an oscilloscope it will be very easy to determine what ...

The flashing is thanks to LEDs with a built-in, integrated flashing circuit and the nasty noise comes from a piezoelectric buzzer — both are available from electronics stores that sell ordinary LEDs.

Signals when an on-circuit battery is exhausted, 5V to 12V operating voltage A Battery-status Indicator circuit can be useful, mainly to monitor portable Test-gear instruments and similar devices. LED ...

Since the LEDs are only attached to the timer's output, the number present won't affect how fast the timer in the simulation cycles. They can still slow the simulator itself down, so I'd put no more ...