Hi Yevgeni,
Questions about your nice parking helper circuit:
1) Doesn't the sensitivity of the circuit depend on the reflectiveness (colour and shinyness) of the wall? Perhaps it should have a sensitivity adjustment.
2) Wouldn't the circuit be more stable by using a lower-voltage regulator? If the car battery's voltage drops much below about 15V, a 12V regulator may drop-out. Perhaps a 9V regulator is more suitable.
3) Using a value of only 33 ohms for the IR transmitter's current limiting resistor, isn't the resulting >300mA of current rather high for the IR transmitter and the 555? However, I do notice the 1:10 duty cycle that reduces the average current.
4) You seem to be using the IR receiver as a photo-voltage source. Wouldn't it be more sensitive if it was used as a reverse-biased photo-conductor (leaks current with IR pickup) or by using an IR photo-transistor and the opamp used as a capacitor-input non-inverting amp?
5) Doesn't C3 charge after a few cycles then without having a diode to discharge it for each cycle, reduce the output voltage of the rectifier?