A software solution is the simplest way to compensate the system offset when interfacing a resistive bridge sensor with an analog to digital converter (ADC) powered by a +5V single-supply power source. "Circuit compensates system offset of a load-cell-based balance" shows how to achieve hardware compensation using a microcontroller which on power-up starts a software routine to reset the system offset.

"Voltage doubler uses inherent features of push-pull dc/dc converter" presents a minimum part count, wide range, voltage doubler using the inherent voltage-doubling characteristics of a one-transformer push-pull DC-DC converter. The circuit exhibits a wide input voltage range from 5V to 30V and provides a typical power output of 1W to 4W at moderate efficiency.  

A simple circuit in "Voltage timer monitors line-connected ac loads" uses a 1-wire counter and opto-isolator to monitor the elapsed time over which a line-connected ac load is energized. You can then access the elapsed-time count over the standard 1-wire protocol.

Powering 20 to 30 white LEDs from three alkaline cells presents an interesting problem for the conventional boost converter. The required boost ratio and duty factor are simply not practical. If you are determined to design with off-the-shelf components, "Cascaded converter boosts LED-drive capability" shows how to cascade two stages of boost.