3 replies to this topic

[starlight]

hi, I just got my Visual Studio 2010 and started hacking last night, so please pardon my uber noobness. I want to record IR signals from my remotes. I measured the signals from an IR receiver diode at about 50 kHz, and saw from the ARM processor data sheet that the Netduino A/D channels can handle 384 KHz. I then wrote the following extremely sophisticated code (you can see I am a jeanous )- public static void Main() { OutputPort led = new OutputPort(Pins.ONBOARD_LED, false); AnalogInput a5 = new AnalogInput(Pins.GPIO_PIN_A5); led.Write(true); // turn on the LED for (int x = 0; x < 100000; x++) { a5.Read(); } led.Write(false); // turn off the LED } I compiled as RELEASE version and let it run. From my stop watch, the blue LED turned on for about 28-31 seconds and then turned off. This means that Im only able to sample about 3,800 times per second, but my remote is throwing signals at 50,000 times per second (as I measured on my OScope). So, this is my summary why I believe this IR capture will never work with Netduino, but its my first project so likely completely wrong. I would like to know where I went wrong, if so- 384.0 KHz : Netduino hardware sampling capability 3.8 KHz : Microsoft .NET Micro sampling capability on the Netduino hardware 50.0 KHz : What my remote appears to be transmitting signals at Does .NET microframework or whatever its called really subtract two orders of magnitude performance from Netduino's hardware? If so, it seems I need a Netduino with a clock speed of 3.8x = 50; x = 50/3.8 = 13 times present speed of 48 MHz, so 625 MHz to handle simple IR remotes, and 5 GHz to realize the full potential of the ARM processor's A/D channels. I sit now in the smoldering wreckage of my first project wondering wtf I went wrong. Can someone please clue me in? I would appreciate it. In return you get this good laugh at my ignorance. Thanks

[CW2]

I want to record IR signals from my remotes. I measured the signals from an IR receiver diode at about 50 kHz, and saw from the ARM processor data sheet that the Netduino A/D channels can handle 384 KHz.

Although Netduino microcontroller is rather powerful, the performance of managed code is significantly lower, because it is interpreted (unlike in 'full' .NET Framework, where Just-In-Time (JIT) compiler translates IL opcodes into assembly). But in all likelihood, 50 kHz is the modulation frequency, you can easily use IR receiver with built-in demodulator or band-pass filter, so you don't have to sample the input signal at such rates. The demodulated output timing depends on particular IR protocol, it is usually slower (~milliseconds) and this can be recorded using interrupts. For example, there is already RC6 decoder and NEC protocol decoder.

[starlight]

Although Netduino microcontroller is rather powerful, the performance of managed code is significantly lower, because it is interpreted (unlike in 'full' .NET Framework, where Just-In-Time (JIT) compiler translates IL opcodes into assembly). But in all likelihood, 50 kHz is the modulation frequency, you can easily use IR receiver with built-in demodulator or band-pass filter, so you don't have to sample the input signal at such rates. The demodulated output timing depends on IR particular protocol, it is usually slower (~milliseconds) and this can be recorded using interrupts. For example, there is already RC6 decoder and NEC protocol decoder.

[starlight]

Thank you for your most helpful reply! It is good to know such limitations..they are just so astonishing at first that they are hard to believe! have a good day