I am new in this forum but I start building the ultrasonic radar circuit for my house entrance, but i got stuck with a couple of questions such as:
1. TR1 is a BC547 or BC548 ??
2. Can I put a buzzer in serial with the colector of TR1, because the relay was not indicated in the circuit i have.
Many years ago I found the Ultrasonic Radar (motion detector) project but today I couldn't find it. Please provide a link to it.
A BC547 is the same as a BC548 except its maximum allowed voltage is 45V instead of 30V. Either transistor can be used in this low voltage circuit.