RRW1 PAIR THEORY OF OPERATION
The RRW1A (transmitter board) may look quite simple but there is actually quite a lot being done inside each one of the parts. Many individual compo- nents are packed inside of the IR receiver part (U2) itself; so many in fact that if it was built up with discrete components, it would never fit in this little kit case. Inside of the part there is an IR detector diode, amplifier, AGC circuit, bandpass filter, a
IR remote controls send out their data on a 38 kHz carrier much like the way your FM radio does. By modulating the carrier signal with the data you want to send, it is possible to increase the range of the transmission and decrease in- terference from other IR sources like ambient light (the sun pumps out lots of IR!!!). The modulation style used with remotes is called OOK (on off keying). In a nut shell, OOK modulation means the IR LED is switched on and off at a rate of 38 kHz in order to send the needed data. The digital data being sent (ones and zeros) is composed of a certain duration pulse for a one and a dif- ferent duration pulse for a zero. There are pauses with no carrier
PWM stands for |
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Modulation, meaning we |
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change the |
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within a certain amount of time. |
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| 1 |
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If we send data at a rate of 1 |
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bit per second (bps), each bit |
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would take up a second of | 0Sec |
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| 1Sec 0Sec | ||||||||
sending time. To represent a 1, |
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the LED may be switched on |
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and off at 38 kHz for 60% of
the one second time frame (0.60 sec.) of it. For a 0, the LED will be switched on and off at 38 kHz for 30% of the time (0.30 sec.) of the entire second.
0
1
RRW1A • 5