11 replies to this topic

[renatoa]

Hi ! I want to do a very specialised device: - a blackbox with two serial ports and a PWM output - one serial port will only listen at 9600bps - the other is bidirectional, - the box will receive various commands on the bidirectional port, and, depending on these commands, will process the input from the first port, and issue a PPM stream on the PWM output. Depending on various processing stages, the speed of the bidirectional port can be changed from 19200 to 115k. Because it was already prototyped in VB.Net on a laptop and it works, seems logical to implement it using Netduino. Is it able to fulfill the above tasks, do you see any limitations ? Any other better approach? Thank you, Renato

[hari]

Netduino has all the necessary ports and features so it should be able to do what you described. It would be interesting to see what it is when you have it completed.
http://netduino.com/netduino/specs.htm

[renatoa]

Well, based on the (lack of) feedback received so far in other threads, I conclude that issuing of a PPM stream is not possible with Netduino, more exactly with the current release of the framework / SDK, probably hardware can do it. So another useless aquisition... If anyone want it, please drop me a PM.

[Chris Walker]

Hi renatoa, What exactly do you need to be able to accomplish this with your Netduino? Chris

[renatoa]

Generate an 8ch PPM frame. The current SetPulse method seems not enough for this task.

[Jan Olof]

Hi Is this what you want to generate http://www.mftech.de/ppm_en.htm A 8 ch RC control frame ? Had no idea what you was talking about so had to goggle . /Jan Olof

[renatoa]

Yes, this is what I want. This is the output of any modular radio system, and the input for RF module

[Jan Olof]

My understanding is that you can´t do that kind of sub mS accuracy pulses from managed code (C#). I think it would be possible from unmanaged code (C++). But there are some much better experts on the forum than me. /Jan Olof

[Chris Walker]

Would the community-created BitBanger work for this? It's coming up on the integration list, but if there's something needed beyond that it would be great to start working out the details now... Chris

[Jan Olof]

Hello Chris My understanding of the bitbanger is that it outputs it´s bits as fast as possible, with a clock to clock in the IO stream into a shift register for instance. But there is no possibility to control how long a output should be on or off. So we would like to have a two dimensional array with logic level, and the time for each signal to be output. I think the bitbanger today executes in a tight loop until clear, and that is okay as it does it´s job very quick. To do what we like för example the PPM signal, I think the program must be interupt driven from a hardware timer, but I don´t know what the interupt latency would be from unmanaged code. I understand it can be quite long in C# code (I think I have read a discussion about this but can´t find it. /Jan Olof

[renatoa]

Thank you for these details, my belief was that at least SetPulse is a hardware timer, if it is software too... Why can't be created objects to drive directly the processor timers ?

[renatoa]

I wonder if someone could implement in as a new class in Netduino, if I have all the required code in C, for an Atmega, using hardware timers ?