IR Emitter and Light Detect sensor

Other Hardware Sensors
1

Dear All
I am just started learning on microprocessor with Arduino Uno. Have been trying out some simple circuit but encounter problem on determining frequency and duration using IR emitter (LD274) and light detect receiver (IS1U60).
When transmit frequency of 40KH tone to IR emitter, the pulseIn reading acquired by Receiver shown in a range of 400-500 usec which not tally with transmitted. Below are some other frequency tried and pulseIn value acquired.
tone frequency Duration pulseIn reading
20KHZ 1 810-865
20KHZ 2 1470-1490
30KHZ 1 735-800
30KHZ 2 1150-1220
40KHZ 1 365-500
40KHZ 2 420-510

I am confuse with the pulseIn readings in relation to the frequency and duration emitted. Can anyone help me how Arduino calculate the reading on serial out of pulseIn base on tone sent?
My sketch as follow:

//SENDER (IR Emitter)
int ir_pinS = 6; //Emitter pin wired through a 220 ohm resistor
int led_pin = 13;
//RECEIVER (Light detector)
int ir_pinR = 7; //IR Receiver pin 1 wired through a 220 ohm resistor

void setup() {
pinMode(ir_pinS, OUTPUT);
pinMode(ir_pinR, INPUT);
Serial.begin(9600);
}

void loop() {
tone(ir_pinS,40000,2);
int time = pulseIn(ir_pinR, LOW);
Serial.println(time);
}

LD274.pdf (37.7 KB)

IS1U60 remote sensor.pdf (50.5 KB)

2

This set-up isn't going to work I'm afraid. The receiver isn't suitable for measuring the frequency of the transmitter because it has a demodulator built in. You need to use a plain IR photo-diode, not an IR receiver. That type of receiver is only good for IR remote control projects (40K should work, but the centre frequency is actually 38kHz).