Ideally I could use the USB port on my oscilloscope instead of the RS-232 port. Why? Because USB is much more commonplace, and it's probably faster.

What's the problem then? I don't know how to interface to the oscilloscope.

GDS-820C uses an FTDI serial->USB converter chip for USB connectivity. It should be as easy as installing the drivers, and connecting via USB.

The latest Virtual Com Port (VCP) drivers should be available for you here: http://www.ftdichip.com/Drivers/VCP.htm

I decided to write this program using python, as I've heard many great things about python.

Here are the packages I'm using:
- pyserial http://pyserial.sourceforge.net/
- matplotlib http://matplotlib.sourceforge.net/
- enstaller http://code.enthought.com/enstaller/


I grabbed pserial from the project page.

Matplotlib is a little different, I opted to download a package from Enthought (the enstaller) which will give me a graphical front end to install some handy python modules.

I followed the "Quick Installation Instructions" @ http://code.enthought.com/enstaller/

Making sure to add the appropriate python directories to my environment path in windows:






After that, load up a command line window and type 'enstaller'

this should load the gui



C:\Users\andrew>echo %PATH%
C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;c:\Python25;c:\Python25\scripts

C:\Users\andrew>
C:\Users\andrew>enstaller
enstaller - version 2.2.0b3 on Python 2.5

Reading http://code.enthought.com/enstaller/eggs/windows/xp...Starting the Enstaller GUI...


At this step I selected to install the following packages:
- matplotlib
- numpy
- scipy
- wxPython

Afterthought: it may be better to install these packages manually..

Open Source SCPI Capture, Oscilloscope Display Program!

Now.. What is the point of this project??

I have an Instek Digital Storage Oscilloscope (GDS-820C) which has a USB & RS-232 serial connection. It came with software to capture waveforms & other data over USB or RS-232 (communicating with the SCPI spec). The problem is: the software sucks. So I decided "Hey, there's an API for this oscilloscope... I could write a better capture program."

And that's exactly what I'm doing.

background
Ok, so what the hell is SCPI? SCPI is an organization&specification for electronics testing equipment. The goal is to make different pieces of testing equipment talk the same language to the outside world. Such as the engineer's computer that is trying to pull the data. If all testing equipment uses the same language to send/receive data, then you could have one program that talks to all of your pieces of equipment. Which is really convenient. There is more info at http://www.scpiconsortium.org/

Tools used:
- python
- open source python modules
- oscilloscope that supports the SCPI protocol

Well, the PIC18F2550 wasn't working for me so I changed to the PIC18F2520.

I don't know why it was giving me problems, but it essentially was not letting me set the clockrate fuses correctly (and I seemed to be missing pieces out of my 18F2550.h file, compared to other people's projects I found on the net.) The only thing I'm really missing is the USB-capability of the 2550, but I wasn't going to use it anyway.

I have completed the PIC code to read from the analog-to-digital converter, as presented in my last post. I have also verified the duty cycle on my GDS-820C oscilloscope.

While the stepper motor could be completely computer-controlled, I'd like to be able to change the speed of the motor by turning a dial. for this i'm using a linear potentiometer from radioshack (10kohm, RadioShack #271-1715.) I'll read the voltage off of the middle pin -- turning the potentiometer will cause this middle-pin voltage to swing from ground to +Vcc (5v in my case). I will read this voltage in via the PIC's analog-to-digital converter and control the motor's speed accordingly.

So today I started on a pic-based stepper motor interface board. This project is designed to interface with a seperate motor controller circuit for the actual motor control, and monitor the rpm's via a sensor -- creating a nice closed loop system. The feedback will be via a hall effect sensor or led reflective/breakbeam setup. I'm not sure yet. Also, eventually I will make my own motor controller circuit, but right now I'm using the BSD-02 motor controller from Interinar. This controller will let me control a bipolar stepper motor, up to 50V @ 2amps. Pretty nice. I can also full-step, half-step, quarter-step, and eight-step.



System Components:

PIC Microcontroller: I'm using the PIC18F2550 with an Olimex development board. The pic will sent the control signal to the motor driver circuit. The pic will also monitor the feedback circuit to determine the real rpm. Furthermore, the PIC will monitor a potentiometer that will be used for speed control. Additionally the PIC will have a serial interface to a PC to display rpm, and possibly accept settings from.

Potentiometer: the potentiometer will control the rpm of the stepper motor. This setting will be read by the A-to-D on the PIC.

Stepper Motor: I picked up from stepper motors for cheap from my friend John at engineeringhobbyist.com and will be using the PowerMax II stepper motors. These suckers are rated for 1.75A operation. 1.8degree full steps. Model #: P21NSXC-LSS-NS-03.

Stepper Motor Controller: like I said, I'm using the Interinar BSD-02 motor controller, and may roll my own later down the road.