If you want to built proto-board conduction tester and keep your sensitive parts save, then you can try this project, In-Circuit Conduction Tester. The project uses an AVR microcontroller (ATtiny13V) to simplify the hardware, a buzzer as output indicator, CR2032 battery as power source and few passive part to make it works.
As we know, that common circuit tester is not suitable to check conduction if wired or electronics component mounted in circuit board. Because, the semiconductor parts in the circuit become conductive under test voltage. Also, the test voltage and current applied to the circuit can damage electrically sensitive parts like IC. By using this tester you can check pure conduction (wired or not) without those problem.
The project firmware reads A-D value and sounds a piezo buzzer. The frequency of beep tone varies depends on the resistance. The frequency starts to lower when the resistance is larger than 5 ohms and stopped at 45 ohms. When no conduction is detected for 5 minutes, it enters power off state. Download: circuit and firmware.