Can't buy a JTAGulator? Then build it – DIY under $75

Hello, everyone! Welcome to this blog where we delve into the motivation and process of building a JTAGulator, an invaluable tool for test engineers, developers, and hackers alike. If you’re looking to identify on-chip debugging interfaces such as JTAG, UART, or SWD, this blog is for you!

Note: Price mentioned includes India import and custom taxes; we ordered in bulk.

Motivation and Introduction to JTAGulator

The idea for this blog came when we realized how challenging it was to source a JTAGulator within India. JTAGulator, an open-source tool by Joey Grand from Grand Idea Studio, is essential for identifying various interfaces on embedded devices.

Protocols Supported

• JTAG
• UART
• SWD
• GPIO logic analysis

The tool lets you configure aspects like input-output voltage, making it versatile. Despite being launched at DEFCON 21 in 2013, it remains a reliable and popular tool among hackers.

Given its rarity in stock, we decided to build our own!

Starting the Build: The PCB

We started by downloading the Gerber file from Grand Idea Studio’s website. As per the Creative Commons Attribution 3.0 Licence, full credit goes to Joey Grand and Grand Idea Studio.

We uploaded the Gerber file to a local PCB manufacturer.
Cost: ~350 INR (~4.5 USD) per PCB.

Download: JTAGulator Gerber Files

Gathering Components: Bill of Materials (BOM)

The Bill of Materials (BOM), available on Grand Idea Studio’s site, includes:

• Quantity
• Reference (e.g., C for capacitor, D for diode)
• Manufacturer & Part Number
• Distributor (e.g., DigiKey, Mouser)

Tip: Some countries enforce import regulations; prepare for customs clearance accordingly.

Assembly and Soldering

With the PCB and components ready, we used the following tools for assembly:

• Solder Paste (Mechanic brand)
• Brush and Blade Set
• Soldering Station & BGA Rework Station
• Tweezers & PCB Holder
• Stereo Microscope for precision soldering
• Multimeter for continuity and voltage checks

Placement of SMD components, especially those with polarity (e.g., tantalum capacitors), required precision. Capacitors, resistors, diodes, and ICs were placed as per the BOM.

Soldering Steps and Troubleshooting

After placement, we:

• Used a multimeter to test for shorts
• Used isopropyl alcohol to clean excess flux

Common issue: Shorts around ICs can prevent USB detection.

Final Assembly and Testing

We followed the test procedure from Grand Idea Studio.

• Checked USB port recognition
• Flashed firmware using Parallax Propeller Tool

Powering Up and Validation

We connected to the JTAGulator via serial console (e.g., GTKTerm) at 115200 baud.

On success, the device displays a welcome message and the LED turns green.

Download Propeller Tool v1.3.2

Final Cost Estimate

Component	Cost (INR)
PCB	350
Components (imported)	~4800
Assembly Tools/Extras	~350
Total	~5500 INR (~66 USD)

Conclusion

With patience and precision, building a JTAGulator can be rewarding and cost-effective.

This DIY approach not only saves money but offers deep insight into hardware debugging.

Embrace the hacker’s way - bruteforce those pins and own the board.

Happy Hacking! 🎉