Can someone say what kind of npn transistor would i use to trigger a ckt which has 9V power supply. For example with this i have attached a ckt in the right most part around 4 transistors are used what r they. Can u please say me the exact product. ? ? ? ?
The circuit to the right is a very, very basic H bridge. Without knowing the motor current there is nothing else to say. If the motor is very small and draws maybe 100 mA then use 2N2222 or 2N3904 transistors. What exactly are you trying to do? Every time the OP Amp triggers the Flip Flop the motor will change direction.
Whole different animal there. Just a single transistor is needed. The flip flop will toggle with each trigger from a whistle blow. Give this link a read paying attention to the base resistor and the use of a diode across the relay coil. Note, the transistor used needs to be able to handle the relay current. For safe operation the 2N2222 or 2N3904 I mentioned holds true at 100 mA for a comfortable margin.
The diode goes across the relay coil to suppress the inductive kick when the coil field collapses. The transistor is used to drive the relay and the transistor is chosen based on the relay coil voltage and current. Did you read the link I posted? It explains things as to selecting the transistor. The 1N part number is a diode and the 2N is an example of a transistor.