Introduction

VUSBtiny is a small in-system programmer (ISP) for Atmel AVR microcontrollers. It allows you to program microcontrollers on the go, without carrying a big programmer with you.

VUSBtiny is based on the USBtinyISP. It uses an Atmel AVR microcontroller running V-USB, which allows it to communicate with your computer via a USB port.

The programmer was not developed by me, but with this repository I added to it in some ways:

• edited the code so that it compiles with the most recent versions of avr-gcc
• designed a PCB for the project, in a way which should make it simple to be hand produced
• wrote this readme, which can help you make your own VUSBtiny.

You can find the original VUSBtiny page here (or here).

License

VUSBtiny is licensed under GNU GPL v2.0. The license is in the file LICENSE.txt. The changes I made are released under the same license.

The V-USB driver is licensed under GNU GPL v2.0. If you intend to use V-USB commercially read this page.

Needed components

To assemble your own VUSBtiny you will need the following components:

• an Atmel AVR microcontroller compatible with V-USB. I suggest ATtiny45 or ATtiny85
• one USB port (male and type A)
• two 68 Ω resistors
• one 1.5 kΩ resistor
• two 3.6 V Zener diodes
• a 10 μF capacitor (optional but recommended)
• a breadboard, perfboard or PCB to assemble the circuit.

How to flash the AVR

The following instructions teach you how you can flash the Atmel AVR you chose to be the brain of your VUSBtiny. I will assume you are using ATtiny45 or ATtiny85. The instructions should be very similar even if you are using others.

With an Arduino Uno

1. Choose a microcontroller compatible with V-USB. You can read about the required specs here. You need at least a 2 kB flash and 128 B of RAM. If you don't want to use an external oscillator your microcontroller must have a 16.5 MHz internal RC oscillator.
2. Setup your Arduino as an ATtiny programmer
3. Program Arduino Uno with the "ArduinoISP" sketch. This step is done without the capacitor between the RESET and GND pins of the Arduino. After you upload the "ArduinoISP" sketch connect the capacitor, as described in the link above
4. Adjust the following options in the makefile:
   • MCU=attiny85, for example
   • possibly adjust PROGRAMMER_MCU also. For ATtiny85/45 this is not needed
   • AVRDUDE_PROGRAMMERID=avrisp
   • AVRDUDE_PORT=/dev/ttyACM0 or to whatever port the Arduino Uno is connected to. You check which port to use by running dmesg right after you connect your Arduino. The last lines in the output should mention some tty port
   • BAUD=19200. This value must match the one in the Serial.begin() in the "ArduinoISP" example
   • change the fuses if needed (FUSE_L and FUSE_H)
5. Do make. The source should compile successfully
6. Do make install
7. Set the fuses (if needed). On ATtiny85/45 we need to disable the reset pin which will be used as a normal I/O pin, which means you will not be able to program this microcontroller anymore using the Arduino Uno. If you need to reverse this step you need a HVSP (High Voltage Serial Programmer).
   • the fuses differ from device to device. The makefile is prepared for ATtiny85/45. If you have another MCU search for a fuse calculator that can aid you setting the correct fuses
   • when you're ready run make fuse

How to use your new programmer

Your newly made programmer will be seen as a USBtinyISP programmer. That means the options you give to avrdude will be the same as if you had a true USBtinyISP connected. Example (flashing a simple blink code):

avrdude -c usbtiny -p t85 -U flash:w:blinkC.hex

You may have to run with sudo, or set correct options in your system.

Troubleshooting

1. Checking if your device was recognised

   Little after you connect the VUSBtiny to your computer if you run dmesg you should see something like this:

    [27548.612082] usb 4-1.5: new low-speed USB device number 105 using ehci-pci
    [27548.639576] usb 4-1.5: New USB device found, idVendor=1781, idProduct=0c9f
    [27548.639587] usb 4-1.5: New USB device strings: Mfr=0, Product=2, SerialNumber=0
    [27548.639592] usb 4-1.5: Product: USBtinyISP
   

   If instead you see only error messages this means the VUSBtiny was not correctly recognised, so it will not work. Try reconnecting.

2. When programming with VUSBtiny avrdude throws Operation not permitted error

    avrdude -c usbtiny -p t85 -U flash:w:blinkC.hex
   
    avrdude: error: usbtiny_transmit: error sending control message: Operation not permitted
    avrdude: initialization failed, rc=-1
             Double check connections and try again, or use -F to override
             this check.
   
    avrdude: error: usbtiny_transmit: error sending control message: Operation not permitted
    avrdude done.  Thank you.
   

   If you see avrdude throwing the previous error back atcha it is probably a permissions problem and you have two options:

   • run the command with sudo or
   • write a udev rule

3. When programming with VUSBtiny avrdude throws initialization failed, rc=-1 error

    avrdude -c usbtiny -p t85 -U flash:w:blinkC.hex 
   
    avrdude: initialization failed, rc=-1
    	 Double check connections and try again, or use -F to override
    	 this check.
   
   
    avrdude done.  Thank you.
   

   If you see this error you probably made a mistake when hooking up the programmer (VUSBtiny) to the target (whatever microcontroller you are programming). Recheck your connections against a 6-pin ISP header pinout and the MISO, MOSI, SCK, RST, VCC and GND pins of your microcontroller.

Improvements

Some improvements that should be made to the PCB are:

• leave more space between the capacitor and the ISP headers. This way the capacitor can be bent to be made horizontal without difficulting access to the ISP header pins

• increase spacing between traces. This is meant to ease manual production and soldering of the board