Voltmeter help!

Nathan,

I hope you have a lot of fun with your project. From your description, you have 2 things to do primarily:

1) Use the ADC of the MSP430 to sample the voltage at a certain pin

2) Convert the code to voltage and display on the 7 segment displays.

The User's Guide for the device is here:
http://www.ti.com/litv/pdf/slau056j

It will give you information on using the peripherals in the MSP430

There are many useful code examples which you can leverage here:
http://www.ti.com/litv/zip/slac019j

Take a look at the many application notes available.

Gustavo

The TCA6507 is a 7 segment LCD driver with I2C connection.

This means, forget abotu the LCD driving capacities of the MSP. You don´t need it. What you need is to

1) use the ADC module to measure the voltage

2) convert it to LCD segments

3) send it via I2C to th eLED driver.

For 1) and 3) there are several threads in this forum. 2) shoudl be relatively easy (worst case, you need to write a lookup table for which digit requires which LED pattern)

Hi,

I have almost the same college project. I am working on a basic multimeter with MSP430. My professor gave me the development tool MSP - FET430U100 and microprocessor MSP430F449. I am a beginner. Up to this days I have never worked with TI microprocessors. And my knowledeges with IAR are very basic too. Last year I worked with ATMEL microprocessors (it was a very old 8051)only and it was quite easy. My project was a simple crossing (cross-roads) cotrol. I have no problems and I finished my work one month ago (before the deadline). So I became proud. But nowadays I am thinking I am lost.....

The TI website is really good, thera are many information, many useful pdfs and tips (advices). My professor gave (and still giving) me a lot of tips too. So I have started to read the User's guide and other pdfs. But sometimes it is really hard for me because I am not a native speaker (I am from Czech Republic) and I am maybe not so clever I need a long time to undestand it. I want to improve my knowledges so I go through the examples and I think it helps me. But the whole problem is to apply it.

The multimeter should measure the DC/AC voltage, current and resistors with the same 7 segment display as in the Nathans' project and even it should be designed for low power. I found there a block diagram of handheld multimeter: http://focus.ti.com/docs/solution/folders/print/591.html But it is too much sophisticated for me.

The tips for Nathan are really good, but do you have some other useful help e.g. Eagle multimeter scheme, other code examples or other users notes (comments)???

Thank you very much in advance and sorry about my English (there are perhaps a lot of grammar mistakes).

John

A multimeter usually consists of the following parts:

1) an input voltage divider.  Since the vonverter usually can only convert voltages in a certain range, you need to break down the input voltage to something in the given range. Usually, you hav a 1:1, 10:1, 100:1 stage (or more). Which one is selected will also control the decimal point on the display later. For a plain voltmeter you only need a simple 1:1 stage, which is no more than a (protective) series resistor

2) a shunt (for converting currents into voltages, if you want to measure currents too. Else you don't need it too.

3)  an effective voltage converter, so AC voltages are converted to the same effective DC voltage. If you want to support AC measurement. If not, you don't need it too.

4) an amplifier stage. Usually, this is unity gain, but if you want to measure voltages below the measurement range of your A/D converter, you need to amplify them. It's the opposite of the voltage divider stage. If you don't need to read very small voltages, you can omit that too.

5) the A/D converter. Most MSPs have them built-in (ADC10, ADC12, SD16).

6) a voltage reference (also built-in, usually for 1.5 and 2.5V or alternatively VCC). This one also determines the range of voltages you can measure and the resolution.

7)  display.

So for the easiest version, you only need a protective series resistor from the signal input to an MSP pin that serves as analog input, two pullup resistors (~10kOhms) on the two lines from the MSPs I2C port to the display, teh MSP itself and some software. Then you can measure voltages from 0 to 1.5 or 0 to 2.5V (depends on software/selected reference) with a resolution of 1.46mv/2.44mv(ADC10) or 0.366mV/0.61mV (ADC12). (I just don't know which one is in the MSP449).

There are several threads about I2C and ADC programming in this forum, partly with code snippets.

Thank you very much for your comment (tips).

The MSP430F449 has got the ADC12 and the reference is 2.5V so the resolution is 2.5/2^12 = 2.5/4096 = 0.61mV as you said.

So I will continue on my work and take a look at this forum threads you wrote.

John Kurik said:

2.5/4096

I am only just getting time to work on this project now, and time is running out!

I am having problems working out how to operate the ADC function of the MSP430F449, I have a voltage source that is to be measured and displayed on the LCD window on the IAR Embedded Workbench.  The output from the ADC will be referenced to a look up table to allow the on screen display.

I aim to input the voltage to P6.0 and use the internal reference feature as comparison.

What would be the best method of getting a basic numerical voltage display on the screen as I am a complete amateur and time is running out!

Also, looking at the data sheet, is the maximum voltage input possible just 3.6V?

Any response will be greatly appreciated.

Nathan

Hi, I'm working in a similar project. I have to do a voltmeter, the source is 120 V-AC, I need measure the frequency, period, THD, harmonics, and display on 7-segments. How can I do?