SFH505A made by Siemens combine infrared diode receiver, amplifier, demodulator and a filter band pass for minimizing interferences. This circuit works together with this infrared transmitter. The output signal of IC1 has the impulse duration limited to a maximum value. This fact is exploited by the associated transmitter to obtain a maximum action radius.
Most commercial remote controllers uses modulated data transfer, in which impulses width are smaller than that IC1 can work. Please note that remote transmitters from Sony or Philips have no effect on this circuit.
D2 diode indicates that IC2a has received a release impulse. If interference occur due to other remotes, this is indicated by D2. The exit of IC3a acts one of the relays through T1. Meanwhile, it triggers monostable IC2b, which operates the second relay on the path IC3b and T2. In this way the second relay is operated from a half-second after the first has been operated. This allows coupling in two steps of some appliances. Diodes D3 and D4 signals relays activation. The relays can switch up to 2000 VA (8A).
The circuit absorbs about 0.6mA when relays are disabled and LEDs are off. With relays and LEDs on, it grows to 125 mA.