How to Build a USBtinyISP: Low-Cost DIY AVR Programmer

Atmel AVR chips power a lot of hobby and embedded projects, small, cheap, well-documented. To get code onto them you need a programmer, and commercial ISPs run $20-$40 for something that’s basically an ATtiny running open-source firmware. The USBtinyISP flips that: it’s a DIY programmer built around an ATtiny2313, costs a few dollars in parts, and works with almost any AVR target (ATtiny, ATmega, etc.).

This post walks through building one.

What you need

• An ATtiny2313 (the microcontroller running the programmer firmware)
• Passive components: resistors, capacitors, a 12 MHz crystal, a USB-B connector
• A 6-pin ISP header to connect to target chips
• A PCB or breadboard

The reference design is well documented, Adafruit’s USBtinyISP guide has the schematic, PCB layout, and firmware image. Follow that for the build.

Bootstrapping: programming the ATtiny2313

There’s a chicken-and-egg problem: to flash the USBtinyISP firmware onto the ATtiny2313, you need another programmer. Any working ISP (a friend’s, a commercial unit, an Arduino-as-ISP) will do, you only need it once.

Once the firmware is on the 2313, the board becomes self-sufficient.

Setting fuse bits

Fuse bits control clock source, brown-out detection, and reset behavior. For the USBtinyISP running at 12 MHz from an external crystal, set:

1avrdude -c usbasp -p t2313 \
2  -U hfuse:w:0xdf:m \
3  -U lfuse:w:0xef:m

If you’re bootstrapping with a serial-port ISP instead of USB, swap -c usbasp for -c stk200.

Using the programmer

Once built and flashed, the USBtinyISP shows up as a USB device. avrdude talks to it out of the box:

1# Read the target chip's signature to confirm the wiring
2avrdude -c usbtiny -p m8 -n
3
4# Flash an ATmega8 with a compiled hex file
5avrdude -c usbtiny -p m8 -U flash:w:firmware.hex

Most AVR toolchains, Arduino IDE, PlatformIO, plain avr-gcc + avrdude, accept usbtiny as a programmer type, so you can use the same board across workflows.

My build

Here’s the board I ended up with:

Related

• Programming a standalone ATmega8 with Arduino code
• Finding the RC constant using an ATmega8
• Introduction to AVR programming