sending ascii commands over serial

[jkupke]

Ok, I know this is incredibly simple but I'm not sure what I'm doing wrong. I have a stepper motor connected over serial. It operates using very simple commands, send w to wake up the motor, send G to step motor. I have no problems controlling the motor through the monitor window. But when I try to use a sequence i get a c1000 channel or function not found error.

I have created the device and it works since it works in the monitor window. I simply need to step the motor

device.stepmotor.write(x)

where x is whatever command i need to send. Is this error because I'm not sending the commmand in the right format? I've tried just typing the G, I've tried Asc(G), I even tried chr(G) even though I'm pretty sure that's converting in the wrong direction.

Any help?

[AzeoTech]

The command expects a string, so:

device.stepmotor.write("G")

If you do:

device.stepmotor.write(G)

DAQFactory will look for a variable named G, which presumably you don't have, which is why you get the C1000 error.

[jkupke]

Ok, that did it thanks

One other question, if I wanted to create an edit box that lets me change these inputs rather than coding them in the sequence, it looks like the edit box will only send values to a channel. I've got it sending to virtual channels I've created. But how do I put that in a sequence? How do I get the value inside the write function?

[AzeoTech]

I do not recommend using edit boxes except for forms inside configuration pages (see the blog). Instead, and especially when you need to do an action at the same time, I recommend using a popup edit box. (button with Set To action) The easiest way to do this is to create a Test String channel, then in the event of that channel, put the command. Something like:

device.stepmotor.write(mychannel[0])

Then whenever you set mychannel to a value it will send it out the serial port.

[jkupke]

Ok, using the test channels worked perfectly. Now I have another question for serial. It looks like the pins that let me read the two outputs from the motors encoder are disabled so I can't just set up a set of quadrature timers. The only way to get position data from the encoder is through the serial connection. There is a setting that causes the motor to send an ASCII "M" every time the motor steps. What is the best way to capture this along with time so I can back speed out of it?

[AzeoTech]

Speed? That's going to be hard because the input gets buffered so you won't get the exact time that the device sent that "M". Also, there's no directional encoding. Personally, I would consider purchasing an encoder and attaching that to the system to get exact position. It will be much more reliable and easier to setup.

[jkupke]

Well the stepper should only fail to maintain speed if it misses a step, which at the torques I'm applying won't happen. If I only want to know the position at certain times, say once a second would that be reasonable?

[AzeoTech]

If its only one direction I suppose you could count the M's coming in. Just create a sequence that reads the port and counts the M's. Something like this (I'm doing this off the cuff):

global pos = 0
private string in
while(1)
   try
	  in = device.mydevice.read(1)
	  pos += (in == "M")
   catch()
   endcatch
endwhile

[jkupke]

So I have the sequence correctly counting pulses, but if i wanted to put these pulse counts to a file how would i code that. I have the following in the sequence at the moment.

private Filehandle = file.Open("c:\stepdata.csv",0,1,1,1)
global pos = 0
private string in
private string stringpos
while(1)
   try
	  in = device.stepmotor.read(1)
	  pos += (in == "m")
	  stringpos =doubletostr(pos)
	   file.Write(Filehandle,stringpos)
   catch()
   endcatch
endwhile
file.Close(Filehandle)

but this is just creating the file. It's not writing anything to the file. My end goal here is to put each count in a file along side a time stamp so that I can later match this data up with another channel.

[AzeoTech]

If your application is small, I'd just create an export set that exports "pos" and run it after the pos+= line. Drop all the file. functions and let the export set handle it for you.

[jkupke]

That worked well for counting the pulses, but when I add another channel that is reading the signal from a load cell, the export stops recording the "pos" variable, I just get the ""time, ,load cell" for each row.

Any thoughts on why the export isn't recording both at the same time?

[AzeoTech]

Data alignment. The load cell channel and the pos channel have different time stamps so they don't end up on the same row. I'd do this:

1) create a new global variable with the load cell reading, let's say "load_cell_log". Have the export set log that instead of the channel.

2) in your event, change this line:

pos += (in == "m")

to something like this:

pos += (in == "m")

pos.time = systime()

load_cell_log = load_cell[0]

load_cell_log.time = pos.time

beginExport(myexport)