I am studying the circuit again. I was not able to understand the use of T1, T2, D1, D2, R1, and R5 on the transmitter part.
On the receiver part, could I change the two transistors to a darlington pair since their function is just to amplify the received signal and tap the output to inverting input of the op-amp?
I will also remove T5 or T6.
And I have never used a relay before. I have read that it is used as a switch, will it control my h-bridge? What I am saying is, with no signal received by the receiver, means no obstacle. The toy car would just go straight. With signal detected, the relay commands my wheels to turn right/or left.