What is it?

This Arduino UNO shield turns your Arduino UNO R3 into a hardware debugger that is able to debug classic ATtinys and ATmegaX8s, such as the ATmega328P. Well, you also need the open-source firmware dw-link.

The hardware debugger speaks debugWIRE with the target chips and has a gdbserver interface to the host. In other words, you can use GDB on your host computer to debug your AVR chip!

The shield provides the following features:

• you can debug 5 V and 3.3 V systems,
• the hardware debugger provides the supply voltage,
• it can supply up to 300 mA,
• it power-cycles the target board in order to enter the debugWIRE state,
• it can program fuses (even in a debugging session),
• and it puts the ISP lines into high impedance state when the lines are not needed.

As a bonus, the software also implements an ISP programmer. So, you can program and debug your target board without changing the connections.

If you want to try this out without buying the hardware, use the quick-start guide.

Why did you make it?

I like the classic AVR chips and use them for a number of low-power projects. What I hate about it is that the Arduino framework does not offer any debugging support for these chips. The alternatives to the Arduino framework are all expensive, proprietary and/or clumsy.

So, I came up with the dw-link Arduino sketch that provides all the needed software functionality on an UNO. However, when you start debugging systems, then you will quickly notice that the basic hardware interface provided by an UNO without this shield is not enough. You also want to handle 3.3 Volt systems, you want to deal with power hungry systems that might need more than 20 mA, and you want to disconnect the ISP lines from the target while you are debugging. So in addition, to the basic debugging firmware, I designed this shield.

What makes it special?

It is a tremendously useful tool and will make your debugging experience awesome. There is nothing comparable out there.

What is included?

You can get either

• the bare PCB (most parts are probably already in your spare part box, and the rest can be acquired easily at your local electronics store),
• a partial kit, which contains the PCB, three logic-level P-channel MOS-FETs (IRLML6402), and the voltage regulator (LD1117V33),
• a kit that contains the PCB and all components,
• a pre-built kit where the three SMD parts have been soldered to the PCB already, you only have to solder the THT parts,
• or a completely assembled kit.

What is not included?

When you want to debug something, you need additionally

• an Arduino UNO R3, on which this shield can be placed,
• a target chip on a dev board with an ISP connector,
• an ISP cable to connect the UNO to the target,
• a USB cable to connect your host computer to the UNO.

How to assemble the kit?

The shield is not really complicated to build. Just follow the assembly instructions, which you find together with the design files in my GitHub repo.