Tag Archives: Graph

C2000, MSP430, Stellaris, Tiva

Code Composer Studio Graphing Tool Tutorial

8 Comments

 

In this Code Composer Studio graphing tool tutorial, graphing variables will be demonstrated in Texas Instruments IDE.  The process is fairly straightforward and will be shown in a video as well as some screenshots so it can be easily replicated.

Introduction

For the demonstration a program running on the MSP430G Launchpad was used, with the MSP430G2553 fitted.  The Launchpad was connected to a small experimental PID boc I have constructed, which I call the ‘Pocket PID’ (tutorial to follow on this), the box uses a LM35DZ temperature sensor as well as a few other components.  The voltage from the LM35DZ is sampled and then two variables are generated; a variable called Result which is comprised of a raw data set of several over samples and a variable called FilteredResult, which is a digitally filtered version of the Result variable.  Both variables can be viewed side by side which allows the effectiveness of the digital filter to be observed, the box also has a small heater and fan which allows the variables rate of change to be viewed over time in a graphical format. This provides a good example of how the code composer studio graphing tool can be used.

The graphing tool can also bee seen in action on another tutorial based on the C2000 Launchpad, where it is used to view the operation of an solar MPPT, graphing the power, voltage and PWM duty cycle.  The third part of the article concerned with this can be found here and the YouTube video here.

Code Composer Studio Graphing Tool Tutorial – Video Demonstration

Code Composer Studio Graphing Tool Tutorial – Main Steps

The main steps to access the the graphing tool in code composer studio (CCS) are carried out in debug mode, so all the screenshot images below are taken from within that mode.  As with all software there are often other ways to achieve the same results, this is just a method that works for me.

The first step is to decide which variables you want to graph and add these as Watch Expressions in CCS, this is achieved by highlighting the variable and then right clicking to bring up a properties menu, from this menu you want to choose the Add Watch Expression selection. This is shown in the below image.

Code Composer Studio Graphing Tool Tutorial Add Watch Expression MSP430 Tiva C C2000

If this has been successful then the variable chosen should then appear in the Expressions window, which is shown in the next image.

Code Composer Studio Graphing Tool Tutorial Watch Expression Visible MSP430 Tiva C C2000

You can add as many watch expressions as necessary, the video demonstration shows two variables being watched and graphed, but I have successfully watched and graphed four expressions.  I am not sure if there is an upper limit, but i have noticed stability issues when many variables are being watched over a long period of time.

After adding the variables required to the watch expression window, the next step is to add breakpoint and then edit the breakpoint properties.  Adding a breakpoint can be achieved either by double clicking on the line number, or highlighting a section of code on the line number and right clicking, then selecting the Breakpoint (Code Composer Studio) and Breakpoint option.  The image below illustrates this action.

Code Composer Studio Graphing Tool Tutorial Add Breakpoint MSP430 Tiva C C2000

Once the breakpoint has been added it should be visible in the Breakpoint window, for the breakpoint to be enabled it needs to have a tick in the far left column.  The image below shows the breakpoint window with the tick in the far left column, as well as an arrow highlighting the Action column.

Code Composer Studio Graphing Tool Tutorial Breakpoint Visible MSP430 Tiva C C2000

 

A breakpoint by default will halt the program at the chosen point, for the graphing tool to work all the windows simply need to be refreshed, this then allows the Expressions window and the graph to be updated.  The next image illustrates how this is achieved by editing the breakpoint properties.  I simply right click on the breakpoint symbol shown next to the line number it will activate, this then brings up a properties list and then select the Breakpoint Properties option. The image below shows this then step.

Code Composer Studio Graphing Tool Tutorial Breakpoint Properties MSP430 Tiva C C2000

Once the Breakpoint Properties window is open there are a few options that are accessible, for this tutorial only one is of interest which is the Action property.  As already mentioned the action the breakpoint will carry out by default is half the program, for the watched expressions to update, this action simply needs to be changed to Refresh All Windows.  The next image illustrates how this is changed.

Code Composer Studio Graphing Tool Tutorial Breakpoint Properties Change Action MSP430 Tiva C C2000

 

Now that the variables have been added and a breakpoint has been placed and set-up to perform the required action, the variables to be graphed can be chosen and set-up.  To bring a graph up for a particular variable, right click on the variable in the Expressions window and then select the option Graph,  as per the image below.

Code Composer Studio Graphing Tool Tutorial Watch Expression Right Click MSP430 Tiva C C2000

Once the graph option is selected the graph should be visible in CCS, I find it usually defaults to the bottom left of the window, as shown in the next image.  The graph window can be manipulated to the required size as well as being picked and placed as required.  Additional graphing windows can be added for other variables in the same way.

Code Composer Studio Graphing Tool Tutorial Tutorial Add Graph Window MSP430 Tiva C C2000

Now the graphing windows also has various options which allow you to tailor the view for your requirements, by hovering over the symbols small tooltips will appear which give a good impression of the button’s action.  This tutorial will only cover two of the buttons which provide enough of an introduction for now.  The first button is the Graph Properties button which is shown in the image below.

Code Composer Studio Graphing Tool Tutorial Graph Properties MSP430 Tiva C C2000

By clicking this button a new window will open which displays some useful quick access properties.  I usually use the Grid Style option to add a Major Grid to the x and y axis, additionally the Display Data Size option allows you to determine how much data is viewable on the graph, before it is pushed off the edge of the screen.  For long data captures increasing the Display Data Size can be useful, I have had issue with instability here though so its compromise on other settings such as Sampling Rate Hz as well as other settings for CCS when in debug mode.  The Graph Properties window is shown in the next image.

Code Composer Studio Graphing Tool Tutorial Tutorial Graph Properties MSP430 Tiva C C2000

The next button that will prove useful is the Graph Display Properties button, this is shown in the next image (also note the Major Grid now shown on the graph window).

Code Composer Studio Graphing Tool Tutorial Graph Display Properties MSP430 Tiva C C2000

The Graph Display Properties window again has quite a few options, allowing things like colour, number formats, axis names and scale to be changed.  Some of these options are demonstrated in the video, the image below shows the Graph Display Properties window and the option for the Y axis Set Number Format option window open.

Code Composer Studio Graphing Tool Tutorial Graph Display Properties MSP430 Tiva C C2000

The final image shows a screen capture from the video, with both sets of data displayed side by side.

Code Composer Studio Graphing Tool Tutorial Video Result Capture MSP430 C2000 Tiva C

I take great care when writing all the tutorials and articles, ensuring all the examples are fully tested to avoid issues for my readers.  If you have found this useful or have any problems implementing, please feel free to leave a comment and I will do my best to help.

C Programming, C2000, Electronics

C2000 Solar MPPT Tutorial Pt/4

32 Comments

 

In this fourth and final part of the C2000 Solar MPPT Tutorial, the system set-up and testing will be looked at.  This will involve the overall hardware set-up for testing, ADC calibration, reduction of noise on the ADC sampling, efficiency test and some improvements for future iterations.  The final C2000 solar MPPT tutorial C code is also downloadable at the bottom of the page.

System Testing

Once the hardware was calculated and designed, the PCB was laid out and then printed using the freeware version of EagleCad.  The PCB was then printed on a LPKF milling machine, the finished component side of the PCB can be seen in the image below.

C2000 Solar MPPT Tutorial PCBThe board was given a thorough visual check, it was noted some of the drill holes on the component side were marginally out of alignment.  This is due to a slight misaligned of the milling machine alignment pins, the bottom of the PCB is milled first and then flipped so the component side can be milled.  When the board is flipped the minor misaligned becomes apparent, it is not enough to cause an issue, but I manually make all my own footprints allowing for the small idiosyncrasies and tolerances of the milling machine.

The components used for the design were mainly sourced from the education institution stock, with only the INA138 being ordered in.  This reduced any unwanted lead times and also keeps costs down.  There are down sides to this which were found with the IRFI640G MOSFETs.  The mistake was made of soldering these directly onto the PCB without checking the MOSFETs first, they were sourced from a large bag of perhaps 500 or more IRFI640G, all previously reclaimed from other boards.  Once the board was constructed it was noted the power supply was going straight into over current protection, this was narrowed down to two faulty MOSFETs that were short circuit, between Drain and Source.  A quick on the fly test I used to check the MOSFETs can be seen in the image below.

C2000 Solar MPPT Tutorial MOSFET Testing

System Calibration

Once the board was working, the next step was to test the buck circuits under controlled conditions,  The test involved the C2000 being set-up to supply a fixed PWM output of 50% duty cycle on PWM1, with PWM2 180o out of phase.  A dummy load in the shape of a 100W potentiometer set to 50Ω was connected to the output terminal, with a 20V supply applied to the solar panel input pins.  A multimeter was used to then measure the output DC voltage, which was observed to be 10V, this confirmed the buck circuit was operating correctly, the 20V was adjusted down to approximately 15V and the voltage was observed to half on the output.

After this initial test the ADC values being sampled needed to be calibrated, this would involve measuring the input voltage and current as well as the output voltage and current.  To achieve this to a good accuracy the same test conditions were used and two Hewlett Packard 34401A multimeter’s.  Some constant values were calculated from the signal conditioning circuitry (see the second part of this tutorial here) used to sample the ADC values, these were calculated as follows.

C2000 solar MPPT Tutorial ADC Constant Equations

These values would then need to be adjusted to meet the tolerances of the circuit.  A laptop was also set-up running Code Composer Studio (CCS) and the calculated ADC variables were viewed, and then the constant calculations values altered until the accuracy was satisfactory. The actual ADC constant values used can be seen in the below code snippet

Various test were carried out at this point to see how the ADC calibration and sampling was working, experimenting with sample and hold times, over sampling.  A useful tool is the graphing feature in CCS this allows trends to be observed in variables.  The original set-up used a timer to trigger the ADC sampling, however this generated more noise due to the MOSFET switching, so the PWM was used to trigger the ADC SOC.

 

The next image shows a screen capture from CCS, with the debug mode in operation.  The MPPT circuit was supplied with 17.5V from a regulated power supply, the load potentiometer was set to 40Ω, a PWM frequency of 25kHz (not 15kHz) with a 50% duty cycle was used in an open loop configuration.

C2000 Solar MPPT Tutorial 25kHz_25SH

What this graphed data shows is a 2 minute sample window (click the image to expand), the top graph is the input current with a variation of 2.4mA, and the bottom graph input volts with a variation of 10mV.  At the top right of the graph the ADC input variable values can also be seen, the two highlighted in yellow just indicates the value has just changed.

Efficiency Test

This basic efficiency calculation test was made by graphing the the input and output power under different power conditions.  The power efficiency fluctuated between 85~93%, with the greatest efficiency being achieved towards mid-range power.  The graphed data can be seen below with the input power at the top and the output power at the bottom.

C2000 solar MPPT Tutorial Power Efficiency Graph

Improvements

This was a prototype design and the first attempt at a solar MPPT, as such there are some improvements that can be made for future iterations.

On the software side, the clock speed for the C2000 could be reduced as there is plenty of idle time, the processor could also be placed into a low power mode between timer interrupts, this would bring an overall reduction in power dissipation.  Additionally a battery charging statement machine could be easily added, with a further form of regulation to switch between full charge and float charge.  If the circuit did not require an interleaved design, the code structure and algorithm could be easily ported across to a lower power and less expensive microcontroller like an MSP430G series.

On the hardware, the MOSFETs are key components that could be changed making the system more efficient.  Greater use of surface mount devices would reduce the circuit trace lengths and noise.  An improved ground plan design would also help reduce noise.  The trace lengths for each circuit phase ideally need to be identical, this will help to balance the phases.  It is possible to sample the current in each phase, then use software to adjust the duty cycle to correct any imbalances, however this increases the overall systems complexity particularly the software.

C2000 Solar MPPT Tutorial C Code Download

The link below contains the zip file with the complete C code, there is a small advert page first via Adfly, which can be skipped and just takes a few seconds, but helps me to pay towards the hosting of the website.

C2000 Solar MPPT Tutorial Full C Code

I take great care when writing all the tutorials and articles, ensuring all the code is fully tested to avoid issues for my readers.  All this takes time and a great deal of work, so please support the site by using the Adfly links etc.  If you have found this useful or have any problems implementing, please feel free to leave a comment and I will do my best to help.