An astable 555 multivibrator circuit, where the timing characteristics are determined by the interplay of an inductor, resistor, and diode.

The simple Diode and LED Tester presented here costs under £5 to build (including all components, the battery and a cheap case) and will indicate the polarity of almost all types ...

This is a pulse generator with adjustable duty cycle made with the 555 timer IC. The circuit is an astable multivibrator with a 50% pulse duty cycle. The difference from the standard design of a 555 ...

But if you’re building your system from scratch you’ll need to add a tone generator yourself. You could use another 555 astable oscillator (using the same circuit as the clock but changing the ...