1. The Sender

 

Click to enlarge

The 555 Timer produces a triangular wave. The potentiometer must be fixed around 5kOhm to get a 40kHz signal. Be precise using the frequency-meter. The phases of the IR and ultrasonic output are not relevant. Here the boards made with EAGLE 4.01 from CADSOFT :

Partlist

C1 3300pF
C2 0.1uF
C3 47uF
D1 IR -LED (GaAIAs-type)

   If_peak=200mA

   (CONRAD part No.171140)
D2 1N4148
D3 1N4148
D4 1N4148
D5 1N4148
IC1 LM555N
R1 1k
R2 10k
R3 1k2
R4 270 (1/2W)
R5 4k7
R6 68 (1/2W)
LEGO RCX-connector
T1 BC107 transistor-npn
T2 BC107 
U$1 ULTRASONIC

 TRANSDUCER 40KHZ (sender)

  (CONRAD part No. 182273)

The beacon is powered by one RCX. Connect the sender's powerline to output A of the RCX. The test-signal is generated by the following small program:

beginoftask(main)

setpower(motor_A,con,7)

loop(con,forever)

   playsystemsound(click_sound)

   on(motor_a)

   wait(con,5)

   off(motor_a)

   wait(con,50)

endloop()

endoftask()

 

The signal output looks like:

N.B. This beacon is not designed for sending a continuous 40kHz-signal. Permanently driven, the frequency decreases to 35kHz due to heat-influence within the circuit. But used as designed, there is no frequency-drift. 

 

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