This Simple remote control tester circuit so use this photo transistor is light receiver from remote control.If it is nice to have bias of transistor BC558
This is the Transistor tester circuit into PCB. When your project do not works, the tester electronic parts or component be what need very much.
This is Coaxial cable tester circuit,to check the cables inside and outside. Check the continuity,short-circuited,detect high resistance, By show with LED [...]
This is 555 audio simple ohmmeter circuit. Some times, we need to measure roughly resistances only. we can know resistances by audio also fast check. [...]
Simple capacitance measurement circuit using IC-555, with the frequency counter as digit number display, that can measure the period.To show value directly [...]
Here is a Simple Continuity Tester circuit using IC-4011. If you are looking for a simple project for kids to learn oscillator on digital.