Ramsey Electronics rrw1b

RRW1B • 5

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. M any individual compo-

nents are packed inside of the IR receiver part (U2) itself; s o 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, am plifier, AGC circuit,

bandpass filter, a peak-hold circuit, an integrator, com parators, and an output

amplifier. Heck, the part is a kit in itself! Just be glad it’s all in one nice module

and ready to go.

IR remote controls send out their data on a 38 kHz car rier 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 transmiss ion and decrease in-

terference from other IR sources like ambient light (the sun pum ps 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 switc hed on and off at a

rate of 38 kHz in order to send the needed data. The digita l data being sent

(ones and zeros) is composed of a certain duration pu lse for a one and a dif-

ferent duration pulse for a zero. There are pauses with no carrier in-between

each one and zero data bit being sent for easy determ ination of the bit

boundaries. A common format for this type of data transm ission is called

60/30 PWM. While this may sound complex, it reall y is not. Let’s take a closer

look.

PWM stands for Pulse-Width-

Modulation, meaning we

change the on-time of the LED

within a certain amount of time.

If we send data at a rate of 1

bit per second (bps), each bit

would take up a second of

sending time. To represent a 1,

the LED may be switched on

and off at 38 kHz for 60% of

the one second time frame (0.60 sec.) of it. For a 0, the LED wil l be switched

on and off at 38 kHz for 30% of the time (0.30 sec.) of the entire s econd.

0Sec 1Sec

IR Remote

Output

IR Detector

Output