Introduction: Cheap Logic Analyzer

About: I'm a mechanical engineer, and I like computer programming, mechanics, electronics and specially the robotics.

If you want to make digital circuits perhaps you need a logic analyzer to log data and analyze them on PC that is very useful for debugging. These tools are not so expensive and you can buy one simply. One day I realized that one of these tools is needed for troubleshooting one of my projects immediately. But I couldn’t find one in my town and buying from internet took about two days to own such a device. So I decided to make a simple one to use at that time. Now I’m going to share my very cheap, simple and fast-making logic analyzer to be made by someone who had a problem like me. But note that the tool I made is not very accurate but could help you a lot. (It was very helpful for me.)

Step 1: Things Needed

According to the circuit diagram to make this tool you need following components and soldering tools and hot glue.

  • About one meter cat5 cable;
  • 1x DB9 female connector;
  • 2x 2.2K resistors;
  • 2x 5.1V zener diodes;
  • Female pin header (7 holes).

Step 2: Assemble All Together

  1. Solder anode of zener diodes to pin 5 of DB9 connector.
  2. Solder one leg of 2.2K resistors to pin 4 and 7 of DB9 connector.
  3. Solder other leg of resistors to the cathode of each zener diode.
  4. Solder cable wires to pins 1, 5, 6, 8 and 9 of DB9 connector and junction of diodes with resistors.
  5. Solder pin header to the other end of cable wires.
  6. Place a label according to the circuit diagram on the pin header.
  7. Use hot glue to fasten wires to the pin header.

Step 3: Ready to Use

Download Cheap Logic Analyzer Software from attached files and run it on your PC. Connect DB9 connector to your PC RS232 port. Start program, select Port (usually COM1) and press Start button to start logging data with this simple logic analyzer, finally press Stop button to stop data logging. If you check the Fast Sampling box, the data is not visible while logging, but the device is able to catch pulses as short as 10 microseconds. (The device speed depends on your PC). You can export data as a CSV file that could be imported to Excel. You can also measure distances on the chart by clicking on it. This device also has two 5V outputs that could be toggled by clicking Output1 and Output2 buttons. You can also write a signal pattern for them using below rules.

  1. Pattern starts with 0; or 1; that indicates initial state of output.
  2. Pattern continues with xxxxx; that xxxxx is the delay time before next state change in microseconds.
  3. If you want to repeat pattern, put r at the end of it.

Example 1: 1;100000;r --> H(0.1s delay)L(0.1s delay)H(0.1s delay)L(0.1s delay)H……..
Example 2: 0;100000;200000;4500;10000; --> L(0.1s delay)H(0.2s delay)L(4.5ms delay)H(10ms delay)L