Measurement question

Foton

What measurement device do I need to make accurate timming measurments on multiple I/O ports at once? I only have a 2 channel digital oscilliscope, but two channels is not enough to monitor multiple channels at once. I know that there are logical analyzers with multiple channels to make measurements, but I have never used one and don't know if this is the tool that meets this requirement. Can anybody give me some advise please?

Thx.
Foton

Franklin

Define accurate and multiple.

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- Stephen

Foton

Stephen,

I will try.

Multiple: using a stamp·I can set miltiple ports to output / input·and control servos·and sensors. While performing these steps I would like to measure high and low voltages as a function of time simultaniously.

Accurate: following program timming execution on these ports, so i can troubleshoot program flow.

I hope this is clear enough.

Thx.

Mike Green

Foton,
Accurate refers partially to some information about the actual voltage range and values you want to measure and the time frame you want to measure them within (including the accuracy of the timing). A Stamp can certainly measure voltages with a few external components, but with limited accuracy and not very quickly at all. Being a "single threaded" processor, it can only do one thing at a time although you can use external analog to digital converters that, in addition to measuring voltages more accurately, can do it quickly and simultaneously with the Stamp doing other things. To answer the question about what you might need, we would have to have some idea of the number of channels of analog information you want to measure, the ranges of those voltages, and some idea of how quickly you want them, how often, and how close to some specific time point (like do you need the readings to be pretty much simultaneous?)
Mike

Foton

Mike,

Thanks for the quick reply. I would like to be able to measure from 0 to 12 volt. I don't know how many channels yet, but for now 8 will be enough. As to the timing I would like them to be pretty much simultaniously.

B.t.w. my english is'nt very good so forgive me for·all the·spelling errors.

Thx.


Post Edited (Foton) : 10/29/2006 7:07:28 PM GMT

Mike Green

The ADC083x series of devices <http://www.parallax.com/dl/docs/prod/datast/dsadc0831.pdf&gt; have from 1 to 8 channels and can measure from 0 to 5V on one channel at a time, but they're pretty fast and could measure all 8 channels in a few milliseconds. Parallax has some examples for the ADC0831 in their 'Basic Analog and Digital' student guide <http://www.parallax.com/dl/docs/books/edu/baad.pdf>, but the ADC0838 is nearly identical. To measure 0 to 12V, you'd only need voltage dividers to reduce the voltage to the 0 to 5V range. You could, if need be, use more than one ADC0838 on a Stamp.

pjv

Hi Foton;

And of course you could measure 8 analog channels EXACTLY simultaneously in parallel, at a rate of about 4 times (all channels in 256 microSeconds) per millisecond. This is using the Parallax Virtual A/D and implementing an 8 channel simultaneous version of it. This is all done with one SX-28 and 2 resisistors plus one small capacitor per channel.

Study the app notes on Virtual A/Ds on the Parallax site, and it will show you how to do it.

Cheers,

Peter (pjv)