![]() ![]() Xpl_dataref_subscribe("sim/cockpit/electrical/instrument_brightness", "FLOAT", new_pwm_xpl)įsx_variable_subscribe("GENERAL ENG THROTTLE LEVER POSITION:1", "Percent", new_pwm_fsx) Driving more than one LED from one I/O pinĪs we said before, you can only drive one LED from one I/O pin. The throttle setting goes from 0 to 100, so to get 0.0 to 1.0 we have to divide the value from the sim by 100. Make the LED shine brighter according to the throttle setting. The brightness value coming from X-Plane varies from 0.0 to 1.0. Make the LED shine brighter according to the set instrument brightness. Bind to Raspberry Pi pin 22, and turn the LED initially off So this script will do different things for different sims. So it will start completely off, then suddenly turn on and increase the brightness from there.ĭue to the limits of FSX and Prepar3D we will take the throttle setting for FSX and Prepar3D, and for X-Plane a very practical example: instrument lighting brightness. LED's cannot be dimmed from completely off to completely on, the LED has a certain threshold at the bottom of the brightness curve. You can find the LED API here: hw_led_add. With the LED API function you can change this 'on time' from 0 (off) to 1 (maximum). When the 'on time' gets longer for one of those 1000 periods, the LED will shine brighter, shortening the 'on time' will make the LED brightness decrease. ![]() PWM turns the pin on and off very quickly, this can happen up to 1000 times a second or even more. The LED can be dimmed by using PWM, which stands for Pulse Width Modulation. Xpl_dataref_subscribe("sim/cockpit2/engine/indicators/fuel_pressure_psi", "FLOAT", new_fuelp_xpl)įsx_variable_subscribe("GENERAL ENG FUEL PRESSURE:1", "PSI", new_fuelp_fsx) Second example, dimming a LED with PWM Subscribe to the data from the simulator. Make the output high (true) if the fuel pressure for engine 1 drops below 25 PSI Bind to Raspberry Pi pin 22, and drive the output initially low In the first example we are going to have a LED that comes on when the fuel pressure for engine 1 drops below 25 PSI. Never connect a LED to the Raspberry Pi without a resistor, not even 'just to try', it will possibly destroy your Raspberry Pi. The positive (anode) side of the LED is connected to a 56Ω resistor, the resistor is connected with a blue wire to I/O pin 22 on the Raspberry Pi. The negative (cathode) side of the LED is connected is connected with a black wire to ground (GND), pin 14 on the Raspberry Pi. In both examples we will use the same wiring schematic. LED connected to the Pi with a 56Ω resistor Dimming is explained in the second example, but if you just want the LED to turn on and off, it's better to use a different (higher) resistor value, because PWM dimming makes it more complex. If you think that the LED is shining to bright for your application then you have two options: use a resistor with a higher value, or dim the LED with PWM. ![]() Resistors come in standard values, a standard value that would come close to 55 is 56 ohm (Ω). Using a LED with a forward voltage of 2.2 and a forward current of 20 mA will result in: (3.3 - 2.2) / 0.02 = 55. R is the resistor value, Vs is the supply voltage (3.3 volt in case of the Raspberry Pi), Vf is the forward voltage (we will use 2.2) and If is the forward current, which typically has a maximum of 20 mA. To calculate what resistor to use there's the following formula: R = (Vs - Vf) / If. In the examples we will use a red LED with a forward voltage of 2.2 volt. Typically the forward voltage of a LED ranges from 1.8 to 2.5, but some LED's consume even more. The forward voltage is the 'negative voltage' used by the LED. When you connect a resistor to the LED it does not matter if you connect it to either the anode or the cathode. The cathode (negative) side of the LED usually has a a flat part. The longest feet is the anode, simply said this is the positive (+) side of the LED, the shortest is the cathode, which is the negative (-) side of the LED. LED's have two feet, one of the feet is a little longer than the other one, and usually the LED has a little flat side. For this example I will go through the forward voltage and forward current really quickly, if you really want to understand it, then please read the Adafruit article carefully. ![]()
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