I recently moved to 4.2 RTM to take advantage of the reduced networking byte-code size which I read about in a forum post on here somewhere. Where does general information about new microframework footprint sizes come from?

Hey Patrick, this may or may not be of any use because it depends on the back-end code for sockets. With the regular .Net framework, socket objects can be disposed but underlying socket resources are maintained by the CLR in the event that in a short space of time, you decide to create a new socket to the same remote host on the same port. This is true even if you call dispose and try to trash the socket as hard as you can. When you use the 'using' clause, it just calls Dispose on the IDisposable object. Your network stream will dispose fine but your socket objects might be doing funny things if the implementation of System.Net.Socket is the same under MicroFramework as it is for regular framework. This is the only thing I can think of that hasn't been explored yet.

If I'm using a dual coil latching relay with voltage of 3V (with coil resistance 129 ohms), do I need to use the transistor ??

It's a bit touch & go with your situation. When they say 129 ohms, they mean total impedance. Part of it is reactive and the other is purely resistive. 129ohms at 3.3V from the CPU pin will draw up to 23mA which is borderline. If you intend on driving the relay in short bursts then it would possibly be acceptable but otherwise you wouldn't.

Once the transient behaviour dies away from switching the relay on, the effective impedance of the relay will be less and you'll exceed the maximum continuous current draw from the CPU pin and smoke the poor thing.

If it was me, I'd use a transistor.

One method I use is to create a socket which is a listener using IPAddress.Any for the binding. The listener will be created if the network is up or down but you can call Socket.Poll(). It will throw a SocketException if the network is down with an error code 10050. The only time this approach fails is if you power the ND+ up and it initially isn't connected to the switch/router. There's some bug which is apparently being fixed in 4.3 where network connectivity to the ND+ is impossible under this start-up condition but the ND+ internally believes connectivity is fine after you plug the network cable in.

Hey guys, Is there a method to check runtime memory usage and possibly get the total memory of the device through micro framework? With the regular .Net Framework you have to do it through a process object but this doesn't apply to .Net Microframework. I've had a skim through all the namespaces for 4.2 and can't find anything relevant.

Hi Nobby,

Try:
int freemem = Microsoft.SPOT.Debug.GC(...);

You can optionally pass in true, forcing a garbage collection, giving you the full amount of memory available.

Chris

That worked a treat, thanks Chris )

Was just about to go to bed and saw this thread. Downloaded the beta framework and installed. Two days ago I downloaded and installed the retail VS2012 Professional. Microframework applications in my solutions now load. I built a 4.2 netduino+ application, deployed and debugged, working fine so far. Will be putting this to a hard test over the next few days and hopefully will be able to do away with 2010.

I have version 4.1 since this is what is recommended in the Download section of this site.



I tried all your suggestions and my browser still doesn't want to connect to the Netduino. I am running the example code from Chapter 8.



I really appreciate the it! Here is a screenshot of my current network settings in MFDeploy:

I noticed in your MFDeploy screenshot that your default gateway isn't in the same IP pool as the DHCP assigned IP address(192.168.5.XXX vs 192.168.1.XXX). Since you're using 24-bit networking, a lot of things are going to go south here. It also suggests that you might have some sort of configuration issue in the netduino or your router.

--Edit my bad: I saw that was your old static IP address.

Hi Guys,

Separately, do you have any sample circuit to connect to N+ for measuring 4-20mA Analog input?
Together with sample code will be great. Currently I am using VB.net to handle the 12V pulse input through opto-coupler circuit.

Thanks in advance.

I don't think you can measure current with a microcontroller. You need to transduce the current to a voltage.

The most accurate method is getting a transducer which uses electromagnetic coupling. It's also the most expensive method.

The easiest method is to use a really small series resistance (1-5 ohms, whatever you can get your hands on) with the circuit you are measuring current. Measure the voltage across the resistance and divide that by the series resistance in your netduino code. The result has errors obviously. Adding resistance to the circuit changes the current. You might also get non-negligable current flow into the analog pin even if it has a high impedence characteristic during analog sampling.

The other consideration you need to be aware of is that 4-20mA is a rather small current to transduce. Mostly because ADC(Analog to Digital Conversion) usually has a precision relative to the operating voltage of the microcontroller(AVR/Netduino) and the value of AREF(usually set to zero volts or Vcc/2). A current that small will produce a voltage so small it will appear as zero after ADC. You'll need to amplify the transduced current signal significantly, especially if you are working in a narrow measurement range (4-20mA).

You can make a simple voltage amplifier with two resistors and an op-amp package.

Hello Alex,

Sound a typical field instrumentation problem.

Use a 250ohms in parallel to 4-20mA signal. Remember V=IR .... V=(4/1000)(250) = 1V...do similar
operation for 20mA and you get 5VDC...right in the acceptable voltage range of the Analog inputs...

Hope helps.

You can't measure the current of a circuit using a parallel impedence, that's only appropriate for voltage measurements(scale conversion). Parallel impedence splits the current through branched paths and it also alters the characteristics of the circuit in a large way(unless the impedence is essentially infinite, 250ohms is very low).

The current transducer circuit has to run in series and have a negligable impedence.

Microsoft.SPOT.Hardware.Utility.GetMachineTime().Ticks has 100ns precision(0.1us) but the accuracy is skewed by +- a few hundred microseconds due to the runtime overhead. If you need to measure an interval less than one millisecond, you end up with an error of about 20% but this error is negligable for slightly larger intervals. The 100ns precision is definitely usefull for cumulative timing functionality. Are you using the timer as a measurement interrupt?

TCP sockets consist of remote and local endpoints by design so naturally you'd assume the state of the connection is managed by TCP but it isn't. The only way to determine the current state of the socket is: -Enforce an activity timeout -Attempt to read from the socket -Attempt to write to the socket In the first case, simply enforce a timeout of a desired interval. If no communications occur within a certain time-frame, forcefully terminate the socket. In the second case, the operation will block indefinitely if no deterministic data stream exists(i.e. client isn't required to send data regularly). If you set a read timeout on the socket, it will throw an exception but this is a false-positive in terms of detecting a client disconnecting. The best method is to write to the socket. This is commonly refered to as Keep-Alive. If the client has closed their socket at the remote endpoint, a socket exception will be thrown at the local endpoint and you can remove the client. Send a single byte or an appropriate byte pattern to the client. They can either absorb the data or make an appropriate response if required. The problem with this approach is that the client is required at at least monitor for this incoming Keep-Alive data. End-to-End data transfer with TCP is fully-interlocked. Even if you perform a write operation on a socket asynchronously, the data backs up in the server's memory(in the netduino RAM in this case) until the client reads all pending data. This is dangerous to server stability. If you are creating an HTTP server, the HTTP specification covers the aspect of Keep-Alive and the client notifies the server through GET/POST methods whether or not they would like the connection to remain open. Even then, this is usually in the order of minutes. HTTP is typically not used for persistent connections though except in the case of data streaming. Good luck

Just noticed that the Netduino Plus forum got renamed so I'm putting my money on a second generation Netduino Plus

Hi Nobby,


There appears to be a bugfix in lwIP to correct this type of issue. .NET MF 4.3 is getting an lwIP upgrade, so we're hoping to have a fix for this soon. [lwIP is a big complicated project and 10,000s of boards rely on it working properly...so introducing the update in beta firmware should help it get some good in-field testing.]

Chris

Thanks for the information Chris

I'm also having ethernet issues with the latest firmware. Although, I can't confirm if the issue exists with older versions. I discovered that the ethernet interface never works at all if a network connection doesn't exist on boot. I made a thread here: http://forums.netdui...h__1#entry32165 Nobody has shared any discussion on the matter. I'm using static IP in this case and absense of network connectivity is fine as long as it occurs after boot/powerup.

Well, I understand the concept and I dont have a problem writing the code for say a 2.4GHz processor x86 with a 4 GBs of ram sampling time of around 1e-6 second easily, the problem I had over here was using this high resolution encoder with a netduino thats all. Just to put things in perspective, if the shaft is rotating at 3 revs/second (180 rpm which is not much )thats 1200*3 = 3600 interrupts/second. I just need help on generating an efficient enough code for the netduino to be able to handle all that along side of some computation thats all. Like I said I am just not used to micro-framework.

There's a couple of ways you can deal with your scenario. If your PID controller is for speed only then the only problem you'll face is convergence speed and possible overshoot depending on your performance specification. Even if the interrupt frequency basically matches the transport delay of the netduino hardware/framework, you just design your PID outer control loop as fast as the device can.

Position control for 3600 interrupts/sec is going to be hard. Depending on how smooth the control needs to be, you would probably have to slow the motor down. If you have to maintain a particular speed range then you'll most likely have jerky position control from lack of controller bandwidth and transport delay.

Although the netduino is capable of 100ns precision timing, most timing functions have 1ms precision. Do you have an option of a lower resolution encoder or do you need to have ridiculously fine position control?