You could read the definition on wikipedia, but as you may already know, I have my way of explaining things to beginner!

I would say that a logic analyzer is a device used to view the voltage of "logic" electric signals that are usually too fast to be measured by a voltmeter. A logic analyzer it not exactly like an oscilloscope, as it cannot measure analog voltages. Actually, it can only measure the logic state of a signal, see if it's a 1 or a 0. '0' being Zero volts and '1' being 5V (for classic TTL logic devices).

The main keypoint that makes a logic analyzer better than another is the sampling rate, or the maximum number of samples that can be recorded by second.

From a functional point of view, a logic analyzer records the states of logic signals, usually after some 'triggering condition' is met, then, recorded signals are displayed on a screen for in depth analysis.

2. Introducing Scanalogic

Scanalogic is a simple, yet effective logic analyzer specially designed to be easily built by beginners, so that it can be used for debugging and analyzing their projects.

It can be used at sampling rates as high as 4 Million Samples per second. It has only 4 channels, but that is more than enough for most hobby projects, further more, most communication buses nowadays have very few transmission lines, ranging from 2 to 4, so decided 4 was more than enough. Scanalogic is a combination of a hardware (figure 2.a) and software application (figure 2.c). As you will see later, the hardware is as simple as it can get: An ATMEGA16 micro controller and a NAND gate! The code to be loaded in the micro controller is provided at the end of this page.

Figure 2.a

The hardware records the samples at the desired sampling rate, then send them to the PC application via the UART port of the microcontroller and the RS232 port of the PC. If your PC doesn't have an RS232 port, as mine, you can still use a USB-RS232 converter cable, as shown in figure 2b.

Figure 2.b

The software is made with visual basic. A setup file is included at the end of the page. It is compatible with windows ME all the way up to XP (or maybe Vista, can someone confirm?). The Scanalogic software controls the hardware (as you can see, there are no buttons on the hardware) It allows you to setup the triggering conditions, to start sampling, to receive sampled signals, display them, analyze them, and even store them for later analysis.

Figure 2.c

3. Building the hardware

There are no secrets held for the hardware, as the real power of this logic analyzer comes from the innovating source code, loaded inside the ATMEGA16 microcontroller.

As you can see in figure 3.b, there are only a microcontroller, and a NAND gates IC and all of it resides in an old CDROM power supply box. The DB9 connector for serial communication is firmly glued to the box with an epoxy resin. The whole is powered from the RTS line of the RS232 connection (pin number 4), so there is no need for external power supply (but you may as well use any 5V power supply if

Figure 3.a

your serial port cannot deliver the required current).

As you can see in the schematic below, there are no level shifting IC like the MAX232, but believe or not, most if not 100% of current serial communication hardware is compatible with the approach below, where the signals are simply 'inverted', but not shifted to +/- 12V. (Originally, in the RS232 protocol, a logic 1 is represented with -12v, and a logic 0 is represented by +12V).

Pin 4 of the DB9 connector is used to power the device, as it rises to +12V (theoretically) when a communication is being carried out. The Diode D3 makes sure no negative power supply is applied to the device, and the 5.1V zener diode D4 prevent supply voltage from rising above 5.1 volts. Using the handshaking signals as a power supply is far from being my invention, it have been used in a lot of devices like mice and old external keypads...

Figure 3.b

The probes are directly connected to micro controller. A better approach would be to add buffers to protect the micro controller but, for simplification, I didn't include one.

The crystal oscillator X1 can be anything from 1Mhz to 16Mhz, but remember that the clock frequency of the microcontroller directly affects the maximum sampling rate, according to the following equation:

Max_Sampling_rate = Clock_frequency/4

That is simply because, the most efficient code I could ever write, needs at least 4 clock cycles to sample and store new signals.

D1 is simply a red LED, used to signal if the device is powered up and correctly functioning.

Download the hex file to be loaded into the ATMEGA16 for different crystal frequencies: - 8 MHz - 12 MHz - 16 MHz (Need hex files for other frequencies? request for it in the forum)

4. Downloading and using the PC side software

Scanalogic software, especially this first version is very simple and intuitive.

After you have plugged the Hardware, the configuration is simply made via 3 steps:
1- Press F2 to chose the crystal frequency at which your microcontroller is running, and to chose the COM port to which the hardware is connected.
2- Press F3 to chose the sampling rate
3- Press F4 to chose the triggering condition

Then you simply need to Press F5 anytime to start the sampling. Note that if you chose a triggering condition, the sampling will only start when this condition is met.

Download the installation file for SCANALOGIC

I hope this article was useful. Any comments and further questions are welcome in the forum below.

Project under construction, register to the forum to get informed of updates by e-mail.

Discussion (Last 15 posts preview...)

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Posted by: ikalogic on: 11 Aug 2010 Re: Scanalogic ['Quote ] Sure! I will add the option to have 10bit address! can you please send me SCL files of the data that you captured? you can send it by mail to ika@ikalogic.com This will be of great help for me to make sure the new decoder is working properly Thank you very much for this feedback! We are always looking forward to update our software

Posted by: whoffmann on: 11 Aug 2010 Scanalogic ['Quote ] Hi, At the moment I aquire I2C-data that have a 10bit address-room (Dallas DS1307 and DS1337). The embedded decoding is not correct (made for 8bit). do you see any possibility for an upgrade with next release? best regards Werner

Posted by: ikalogic on: 10 Aug 2010 Re: Scanalogic ['Quote ] this is most probably a power supply problem, Try powering the device from an external 5V..

Posted by: dixonsteel on: 09 Aug 2010 Scanalogic ['Quote ] A little further info... The errors and omissions were my mistakes that I corrected. I just put in another 16L and used this line to program it: avrdude -c usbtiny -p m16 -U flash:w:logic_analyzer_16Mhz.hex I'm sure it is a fuse problem as the LED is now lit again. I'm still getting the error on startup though. I feel I'm very close and would appreciate any help. (Also, am I correct in assuming that the device does not have to be attached to a circuit under test to work? I mean that with the analyzer and software running it does not have to be 'in use' to be error free?) Thanks!

Posted by: dixonsteel on: 09 Aug 2010 Re: Scanalogic - fuses ['Quote ] Hi, I built the project and had to correct a few errors and omissions. I finally got it programmed using usbtinyisp. I used 16mhz crystal and used 16mhz hex file. LED is on (or, it was on). Each time I started software I got error message. It would connect to com port COM1, but would say it could not communicate with device. I did some fiddling and tried to set fuses. I think I messed it up. The LED no longer lights and usbtinyisp no longer sees it. Do you think the fuses the original problem? What would be the command to set them correctly if I replace the mega16L? Paul

Posted by: kakzai on: 02 Aug 2010 Scanalogic ['Quote ] Dear Sir Can't i request hex file for crystal frequency 4 MHz ? Thanks you very much before http://www.ikalogic.com/scanalogic_home ... mini_forum

Posted by: nachi on: 06 Jul 2010 Scanalogic ['Quote ] Dear Sir Thank you so much for the wonderful guidance and prompt reply . Wish you all the very best for your upcoming projects and may you achieve success to your satisfaction. Best regards Nachiket.

Posted by: ikalogic on: 05 Jul 2010 Re: Scanalogic ['Quote ] No, but various users have provided the hex file for M32, you will find it among the 20 pages this thread...

Posted by: nachi on: 05 Jul 2010 Atmega 16 L to Atmega 32 possible with same HEX code ? ['Quote ] Dear Sir Can the Atmega 16 L chip be replaced with that of an Atmega 32 in the circuit and be burned with the same hex file ? Awaiting reply . Thanks in advance. Regards Nachiket Kalantre

Posted by: yan78 on: 08 Jun 2010 Re: Scanalogic ['Quote ] Ika ! Even with one channel I could do a a lot of work on a Weather transmiter protocol. It's a wonderfull tool . I will try to find more time to resolve that bug in software . I will post this problem in arduino forum . Maybe someone will have more time so solve the problem . Bye !

Posted by: ikalogic on: 07 Jun 2010 Re: Scanalogic ['Quote ] Quoting Yan78: New release! Scanalogic with 2999 samples . Serial speed 115200 bps , DTR deactivated so Arduino will not restart . It will work only with Arduino based on ATMEGA 328 - 16 Mhz . ONLY CHANNEL ONE IS WORKING . Did not had time to investigate ! Thanks yan for all the efforts!! did you get any luck with other channels? besides, i am not Arduino user at all, but are other Arduino fans out there aware of that? maybe we can let them work with you on that!

Posted by: yan78 on: 04 Jun 2010 Re: Scanalogic ['Quote ] New release! Scanalogic with 2999 samples . Serial speed 115200 bps , DTR deactivated so Arduino will not restart . It will work only with Arduino based on ATMEGA 328 - 16 Mhz . ONLY CHANNEL ONE IS WORKING . Did not had time to investigate ! See attached file(s)

Posted by: yan78 on: 03 Jun 2010 Re: Scanalogic ['Quote ] Another version for Arduino now adata is 2000 samples large . But someone will have to modify the source in Visual Basic for Scanalogic . Onlz channel 1 is working ( I didn't had time to find why because I'm playing with some decoding for a 433 Mhz weather receiver ) See attached file(s)

Posted by: yan78 on: 03 Jun 2010 Re: Scanalogic ['Quote ] It's working better without Timer0 overflow int. activated . line 1323 in source file //TCCR0B = (1<<CS00)|(0<<CS01)|(1<<CS02); //TC2 counts Clock_io/1024 SREG = 0x80; //enable general interrupts in SR //TIMSK0 = TIMSK0 | (1<<TOIE0);//Enable timers interrupts //TCNT0 = 0;

Posted by: yan78 on: 03 Jun 2010 Re: Scanalogic ['Quote ] Ika ! your solution was good . But I don't know why is only sampling for channel 1 . For those ho want to try and to upgrade the software this is the code . See attached file(s)

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