The old circuit v1 is based on 555 IC, for which needs more discrete components and can't connect the IR diode / photo diode directly without an amplifier.

So, if an amplifier is used cheapest one available is an LM325, which is a dual OpAmp package, so instead of using a 555 to create a single pulse / one shot / monostable circuit. The same can be achieved using an OpAmp.

OPAMP 1 : Sensor / Signal amplifier.

OPAMP 2 : Monostable / One Shot circuit.

So, whoever wanting to create a project using these circuits, please wait for V2 of circuit, which will b cheaper and more reliable.