AVR based logic analyzer. - Electronic Circuits Projects Diagrams Free

ikalogic · 10th May 2008, 08:06 PM

Hello,

I've been working from a couple of weeks on building a logic analyzer using an ATMEGA16 microcontroller.

my fist goal is to make a 4 channel, 1MHz sampling rate analyzer. Future development are on the way.

The connectivity to the PC would be via RS232 (or USB via a USB to RS232 cable)

The PC will have a Visual basic program to receive all data an draw it.

My goal is also to make the visual basic program capable of decoding UART, SPI, I2C, and CAN buses.

I have already solved the PC to ATMEGA16 connectivity problem. I have also found a *new* idea to auto-correct the timebase of the ATM EGA based on the RS232 clock..

I have successfully coded the inline ASSEMBLY codes for 1MHz sampling.

Sooner or later i should start on with the hardware implementation.

My question: are people here interested in such a project? I am planing to take lot of pictures during the building of the project, and make the software available for download with documentation. That will be a lot of work, and i'll be happy to do it, if i feel that it of some interest to you.

Is it?

I also hope there will some active participation and suggestions from fellow members, which is logical considered such a project/software will be interesting for the electronics and robotics community.

Waiting for your comments.

Regards.

**3v0** · 10th May 2008, 09:12 PM

I am interested but would much rather see USB for PC connectivity.

ikalogic · 10th May 2008, 11:19 PM

Well, i am actualy gonna use the RS232 TO USB cable to use it on my laptop..

ikalogic · 10th May 2008, 11:30 PM

anyway.. i feel like the community here - to my surprise - is not very motivated about such a project...

blueroomelectronics · 10th May 2008, 11:53 PM

The PICkit2 has a builtin 3 channel 1mhz logic analyzer built in to the software. USB too.

ikalogic · 11th May 2008, 12:00 AM

Quote:

Originally Posted by blueroomelectronics

The PICkit2 has a builtin 3 channel 1mhz logic analyzer built in to the software. USB too.

Well, i am building it anyway, and i love AVR and ATMEL! every one got his fans!

lol, anyway, i wanted to ask, is 1MHz logic analyser means that it can sample clearly signals at 1Mhz, or that it takes 1 Million samples per second?

gramo · 11th May 2008, 12:05 AM

I think it sounds great Ika

I've played around with VB quite a bit with regards to UART, but not with USB unfortunately..

If you keep it simple, then the raw programming of the micro will be minimal, especially if you use UART

The Logic Analyzer;

Monitor the status of the Pin and when it changes send a byte through UART with the relevant information (high/low). The VB program will display a running image with the data with its refresh rate (time scale) being changeable by the user.

The time it takes to send one byte via UART will be your smallest resolution. Its crude, but it will work for a simple logic analyzer, and will get decent speeds with a fast enough UART.

The Oscilloscope;

This will require bi directional UART, primarily for setting the time scale. Create a routine that waits for a positive zero crossover, and then grabs 256 samples and stores the data into an array.

The time between samples could be extended with NOP's or by burning cycles (as required by the user on the VB side of things). Send the 256 bytes of data to the PC, for display on the VB program. It simply maps the 256 ADC values on a graph and waits for the next signal.

Your thoughts?

Sorry about your post on my site BTW, I used Web Expressions to update the site instead of a standard ftp program, problem is, it deleted all folders that were not found locally on the computer - the forum being one of them.

blueroomelectronics · 11th May 2008, 12:08 AM

I'm not at my computer but I recall it alises @ 500kHz. Handy tool either way, plus a UART tool too. Not too shabby for an inexpensive programmer / debugger.

gramo · 11th May 2008, 12:22 AM

Quote:

Originally Posted by ikalogic

Well, i am building it anyway, and i love AVR and ATMEL! every one got his fans!

lol, anyway, i wanted to ask, is 1MHz logic analyzer means that it can sample clearly signals at 1Mhz, or that it takes 1 Million samples per second?

You can take a sample every 1/1000000 of a second. Say your display contained 64 co-ords for displaying the captured data, this means that 1/(1/1000000 * 64) is the fastest sine wave you can sample, this of course limits the max frequency it can sample too 15.625 KHz

You can go faster, but you will not be able to sample the complete sinusoidal signal, or decrease the resolution of the result

Zero crossover detection is simple,

Code:

While True
    // ensure the signal is below zero crossover
    Repeat
    Until Adin(0) <= 511

    // wait for the signal to go positive above zero crossover
    Repeat
    Until Adin(0) >= 511

    // take samples
    Sample = 0
    For Sample = 0 to 64
        ADCSample(Sample) = Adin(0)
        DelayuS(TimeScaleFactor)
    Next
    
    // write data to UART
    USART.Write("New Sample")
    Sample = 0
    For Sample = 0 to 64
        USART.Write(Convert.DecToStr(ADCSample(Sample))
    Next

Wend

Thats almost my whole OSC program, but I can't find the origianls since re-installed windows. Both the Delay and Adin modules were modified to provide application specific speeds/delays

ikalogic · 11th May 2008, 12:27 AM

Quote:

Originally Posted by gramo

I think it sounds great Ika

The time it takes to send one byte via UART will be your smallest resolution. Its crude, but it will work for a simple logic analyzer, and will get decent speeds with a fast enough UART.

Well, the interesting part of my project it that i wont rely on the speed of UART to transfer the states of the 4 channels... i will store them immediately on the micro controller (i could store up to 2000 samples per channel), while still leaving like 500 bytes of free memory for my program variables. then they would be sent to the PC. A trigger signal would initiate the sampling cycle (it could be rizing/falling edge, etc..)

I however intend to give the user the possibility of "free running" analyzer, where the 4 channels will arrive at the same speed of the UART, this mode will allow the user to see the channels live, but won't be optimized for speed..

gramo, i have a question, with 1 MHz sampling rate, what is the maximum frequency of the signal that can be analyzed clearly.. if you see what i mean?
In other words, how much higher the sampling frequency has to be than the measured signal frequency for acceptable results?

and about the OSC, thanks but i really want to stick to the logic analyzer for now.. one thing at a time! but thanks anyway

gramo · 11th May 2008, 12:43 AM

Quote:

Originally Posted by ikalogic

I however intend to give the user the possibility of "free running" analyzer, where the 4 channels will arrive at the same speed of the UART, this mode will allow the user to see the channels live, but won't be optimized for speed..

This will suite most applications given the target audience I'd imagine

Quote:

Originally Posted by ikalogic

gramo, i have a question, with 1 MHz sampling rate, what is the maximum frequency of the signal that can be analyzed clearly.. if you see what i mean?
In other words, how much higher the sampling frequency has to be than the measured signal frequency for acceptable results?

Seems we are posting in and around ourselves

I posted an example earlier, but also forgot to mention that the impedance of the sample will be a factor given the time it takes to charge/discharge the internal capacitors on the micro side of things. For most applications this isn't and issue, but for some high frequency, and high impedance samples, there results will not be 1:1

Quote:

Originally Posted by ikalogic

and about the OSC, thanks but i really want to stick to the logic analyzer for now.. one thing at a time! but thanks anyway

Nps, just putting it out there for you

gramo · 11th May 2008, 12:47 AM

Quote:

Originally Posted by ikalogic

In other words, how much higher the sampling frequency has to be than the measured signal frequency for acceptable results?

Sorry, I didn't explain that bit, I came from the oscilloscope perspective working with the frequency of a sinusoidal wave.

Your resolution will be limited by the code overhead of the samples for the logic analyzer, from there you can calculate the error/max frequencies attainable

ikalogic · 11th May 2008, 02:36 AM

Let me put it this way:

i allready managed to write the code to achieve 1MS/s.

What is the max frequency of the signal that can be sampled? 2.5 times less as some websites say, although i am skeptic..? or what?

thanks for your enlightening!

**3v0** · 11th May 2008, 06:26 AM

Have you seen this? I am not suggesting anything by pointing it out other then it is an interesting open source LA effort.

FLASH - PLAICE: Programmer, Logic Analyzer and In-Circuit Emulator Project

eblc1388 · 11th May 2008, 07:52 AM

Quote:

Originally Posted by ikalogic

What is the max frequency of the signal that can be sampled? 2.5 times less as some websites say, although i am skeptic..? or what?

Besides frequency, things just don't all happen at the same time.

Ask yourself this simple question:

If there are two logic levels changing one after another, will my sampling frequency will be fast enough to catch and distinguish them?

E.g. You have two 1KHz square signals. The rising edge of the second one lags the first one by 100ns. Will the sampling results tell them apart? What if they differs by 500ns or even 1us?

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10th May 2008, 08:06 PM	(permalink)
ikalogic	AVR based logic analyzer. Hello, I've been working from a couple of weeks on building a logic analyzer using an ATMEGA16 microcontroller. my fist goal is to make a 4 channel, 1MHz sampling rate analyzer. Future development are on the way. The connectivity to the PC would be via RS232 (or USB via a USB to RS232 cable) The PC will have a Visual basic program to receive all data an draw it. My goal is also to make the visual basic program capable of decoding UART, SPI, I2C, and CAN buses. I have already solved the PC to ATMEGA16 connectivity problem. I have also found a new idea to auto-correct the timebase of the ATM EGA based on the RS232 clock.. I have successfully coded the inline ASSEMBLY codes for 1MHz sampling. Sooner or later i should start on with the hardware implementation. My question: are people here interested in such a project? I am planing to take lot of pictures during the building of the project, and make the software available for download with documentation. That will be a lot of work, and i'll be happy to do it, if i feel that it of some interest to you. Is it? I also hope there will some active participation and suggestions from fellow members, which is logical considered such a project/software will be interesting for the electronics and robotics community. Waiting for your comments. Regards. __________________ Ibrahim Kamal check my electronics and robotics page: http://www.ikalogic.com/

10th May 2008, 09:12 PM	(permalink)
3v0	I am interested but would much rather see USB for PC connectivity. __________________ search engine for electronic parts Junebug USB PIC programmer kit., USB Bit Wacker, Homepage The 15 Minute Printed Circuit Board! (+drill time)

10th May 2008, 11:19 PM	(permalink)
ikalogic	Well, i am actualy gonna use the RS232 TO USB cable to use it on my laptop.. __________________ Ibrahim Kamal check my electronics and robotics page: http://www.ikalogic.com/

10th May 2008, 11:30 PM	(permalink)
ikalogic	anyway.. i feel like the community here - to my surprise - is not very motivated about such a project... __________________ Ibrahim Kamal check my electronics and robotics page: http://www.ikalogic.com/

10th May 2008, 11:53 PM	(permalink)
blueroomelectronics	The PICkit2 has a builtin 3 channel 1mhz logic analyzer built in to the software. USB too. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

11th May 2008, 12:05 AM	(permalink)
gramo	I think it sounds great Ika I've played around with VB quite a bit with regards to UART, but not with USB unfortunately.. If you keep it simple, then the raw programming of the micro will be minimal, especially if you use UART The Logic Analyzer; Monitor the status of the Pin and when it changes send a byte through UART with the relevant information (high/low). The VB program will display a running image with the data with its refresh rate (time scale) being changeable by the user. The time it takes to send one byte via UART will be your smallest resolution. Its crude, but it will work for a simple logic analyzer, and will get decent speeds with a fast enough UART. The Oscilloscope; This will require bi directional UART, primarily for setting the time scale. Create a routine that waits for a positive zero crossover, and then grabs 256 samples and stores the data into an array. The time between samples could be extended with NOP's or by burning cycles (as required by the user on the VB side of things). Send the 256 bytes of data to the PC, for display on the VB program. It simply maps the 256 ADC values on a graph and waits for the next signal. Your thoughts? Sorry about your post on my site BTW, I used Web Expressions to update the site instead of a standard ftp program, problem is, it deleted all folders that were not found locally on the computer - the forum being one of them. __________________ Spency. PIC Micro's - Your mind is the limit PIC's and interfacing with other devices - a PIC Basic Guide @ digital-diy.net

11th May 2008, 12:08 AM	(permalink)
blueroomelectronics	I'm not at my computer but I recall it alises @ 500kHz. Handy tool either way, plus a UART tool too. Not too shabby for an inexpensive programmer / debugger. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

11th May 2008, 02:36 AM	(permalink)
ikalogic	Let me put it this way: i allready managed to write the code to achieve 1MS/s. What is the max frequency of the signal that can be sampled? 2.5 times less as some websites say, although i am skeptic..? or what? thanks for your enlightening! __________________ Ibrahim Kamal check my electronics and robotics page: http://www.ikalogic.com/

11th May 2008, 06:26 AM	(permalink)
3v0	Have you seen this? I am not suggesting anything by pointing it out other then it is an interesting open source LA effort. FLASH - PLAICE: Programmer, Logic Analyzer and In-Circuit Emulator Project __________________ search engine for electronic parts Junebug USB PIC programmer kit., USB Bit Wacker, Homepage The 15 Minute Printed Circuit Board! (+drill time)