2. The receiver

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One part of the circuit is a stabilized +5V power supply which should be connected to an RCX output. It gives also the reference voltage (=2.5V) to the amplifier. The ultrasonic receiver is linked to the amplification stages, followed by the peak detector and a comparator to trigger the signal, which is then transfered to the PIC-microcontroller. (Use the oscilloscope and the RCX-beacon when calibrating.) The IR-detector's signal is dephased by 180°and then sent to the PIC. The output is the one we described already at the phase-sound's page. We added a 5th stage to the resistor-net. The relevant resistor has only 1kOhm. We use this small value for special messages. Don't forget to connect the optocouplers to an RCX input while observing the polarity this time. The PIC is clocked by a 4MHz quartz. The trigger point must be found through the potentiometer. 

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NOTE: You may as well use the IR-receiver Sharp GP1U57X. Note that these IR-detectors only react on a modulated signal.

Here a typical receiver response:

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