The infrared wireless port when updating a
It is a bit more complex than appears at first glance, since the start bit must be zero for the 10-bit serial port input hardware to work, and the IR receiver inverts the signal.Note: If the status shown is "In Progress", check again later.To keep it simple in each case, 8-bit ASCII character data will be sent out over the link and received back using mbed's serial port hardware.A terminal application running on the PC attached to mbed's USB virtual com port will be used to type in test data.At a range of just a few inches the receiver can pickup the signal from the side, if case you have trouble pointing it directly towards the IR LED.
TV remotes use an Infrared LED Car key fobs use RF Using some low-cost parts and breakout boards that should only cost around US per demo, two basic demos will be setup. Each demo has a transmitter and matched receiver attached to mbed.
Sparkfun IR LED transmitter module The Sparkfun IR LED breakout board seen above contains a 50MA high output IR LED and a driver circuit using a transistor as seen in the schematic below.
An IR Led can be used instead now that this board is no longer available, but the circuit still needs the correct polarity to control the LED on/off state, since the serial port's internal UART receiver hardware must have a low start bit and a high stop bit to work.
IRLED = .5 generates a 50% PWM duty cycle to produce a 38Khz square wave for the carrier.
The gnd pin on the IR LED is actually switched on and off using mbed's serial data output to eliminate the need for any external digital logic, and still permit direct use of the serial port hardware for 38Khz IR data transmission.