Digital

This simple TTL power supply monitor circuit monitors the 5-volt level TTL power line and gives a signal whether the supply voltage is outside or within the necessary range or “window”. The heart of the power supply monitor is a low-current integrated window comparator. The center of this window is set at 2.5 volt +/- [...]

The diagram shows the circuit of a versatile USB power socket that safely converts the 12V battery voltage into stable 5V. This circuit makes it possible to power/recharge any USB power-operated device, using in-dash board cigar lighter socket of your car.
The DC supply available from the cigar lighter socket is fed to an adjustable, three-pin [...]

The LM555 timer can achieve a 50 percent duty cycle as shown in the next diagram. The duty cycle adjustment range of the give components values is from 42 to 55 percent.
Resistors R1 and R2 were selected first and then resistor R3 was selected to give the best control range based on [...]