Starting from below, we notice the IR1 infrared receiver, whose output is directly read by Arduino/RandA’s D6 line, during the learning phase, from the “original” remote control. The very well-known DS18B20 temperature sensor is connected to D11, so to return the environment’s temperature to the user. By still going up, we reach the T1 bipolar transistor, used as an electronic switch controlled by the D5 line (configured as an output), that is programmed by the sketch so to apply the modulated signal, which is relative to the channel we want to broadcast. The choice of D5 was not a random one, since it corresponds to the TCCR0 timer’s output, used to acquire the modulation frequency.
The LD3÷LD5 infrared diodes (driven by this signal) send the data in the form of infrared light pulses: with a 5V power supply and a (R5) series 22Ω resistor, the direct current in the diodes’ series is confirmed at about 50mA, a value that allows a transmission at a distance of about two-three meters (the exact range also depends on the alignment among the photodiodes and the receiver, and on the sensibility of the latter). To further increase the range, the power must be increased, and that can be achieved (by decreasing the electrical resistence’s value and/or by increasing the voltage), provided that the duty-cycle of the signal applied to T1 is reduced (by decreasing the ratio between the starting and switching off times) in order to avoid damaging the same diodes. A yellow LED (LD6) is also connected to the T1’s base, and it is used to monitor the execution of the transmission cycles (it will flash quickly during the transmission).
LD1 and LD2 LEDs are needed in order to display the system’s status during the execution of the various phases (as we will explain later), while P1 and P2 are needed in order to give orders, specially if concerning the acquisition phase (and they will be seen in detail later, as well).
Finally, U1 is an EEPROM memory, managed via I²C bus, and needed to memorize the codes of the acquired channels: by using a 24LC256 (32 kB) type memory, up to 127 different codes can be memorized. We had to recur to an external memory since Arduino microcontroller’s internal EEPROM has a limited capacity, one that doesn’t allow the memorization of more than four channels.
Let’s pass now from the hardware to the software, by going to see how the shield we just described is managed.
The program for Arduino resident in RandA has been developed as a finite-state machine, whose diagram has been summarized. From the idle state, with both LEDs turned off, it keeps waiting that a button is pressed or that a command arrives from remote (from a web page, that -as we will see later- from Arduino’s point of view corresponds to receiving some characters on the serial port).
By pressing P1 we enter the acquisition mode from the remote control: the red LED will flash, thus informing that the user has to click the key (on the virtual keyboard of the web page) he wishes to associate with the remote control’s code that will be acquired. If the operation is not completed within ten seconds, the phase will be aborted and the system will return to the wait state. Vice versa, the LED will turn on with a fixed light, to indicate that the wanted button on the remote control has to be pressed (after having “pointed” it towards the IR1 infrared receiver, at a distance of about 10 cm), so to send the code to be acquired. Once this has been done, the green LED should turn on for about five seconds, so to indicate the correct learning of the new code. Even in this case, a time-out is present: if within a short time the infrared signal doesn’t arrive, the red LED will flash three times so to warn about the operation being unsuccessful, then the machine will return to the wait state.
Please notice that the acquisition phase can only be activated by pressing the P1 button, and not from the web page. This solution has been chosen mostly in order to avoid that, by remotely activating it by mistake, some channel may be overwritten. Anyway, having to press the button is not a problem, since we have to be near to the board in order to “point” the remote control (from which to learn the codes) at it.
Let’s return to the diagram: if from the wait state we press P2, the red LED will flash two times so to indicate that the local mode has been activated, meaning that the acquisition and communication operation can be carried out by acting on the two buttons, thus without having to connect “remotely” by means of the web page. This option enables the usage of the system in the “stand-alone” mode, for example to make a quick operation test, even when we are far from a PC.
The only limitation is that we do not have the virtual keyboard, and therefore we chose that learning or communicating will regard the first channel only. The operating mode is clear from the diagram: once we enter the “local” operation mode, by pressing P1 the acquisition phase will be activated, with the red LED turned on with a fixed light, waiting to receive a code from the remote control (the code will then be saved, as we explained before, on the number one channel). On the other hand, by pressing P2 the red LED will flash three times and the IR communication will then be activated.
Finally, if from the wait state a command is received from remote, the IR communication is activated for the channel whose number is specified by the command itself (that obviously corresponds to the relative button clicked on the web page). A command has then been added, and it is identified by the (number of channels +1), that asks Arduino to read the temperature from the DS18B20 sensor and then to send it back to the web page.