programming pen usb interface

Posted on Feb 5, 2014

Trigger programming with its build-in pushbutton. The solution I came up with was to add a tiny USB keyboard circuit to the pen`s interface. One method to have the pushbutton trigger a programming command would have been to add a microchip to the pen`s interface and connect it to the PC using a USB to serial converter. The microcontroller could then sent some

programming pen usb interface
Click here to download the full size of the above Circuit.

data to the PC every time the button is pushed. However, that would also required a script on the PC side to check whether the pen was sending data. What I wanted was a universal interface, which could be used to program any type of microcontroller, which wouldn`t require any scripts or drivers. What I came up with was to add an USB keyboard interface to the pen. In order to make the pen work no matter which command needs to be executed to program a chip, I decided it would send the arrow up keystroke followed by an enter. That way, I can just type the programming command (e. g. "make flash") once in a terminal window and pressing the programming pen`s button afterwards will make the same command execute. I did not want to increase the size of the programming adapter, so my build space was extremely limited. I found V-USB, a software USB driver for Atmel AVR chips. That website contains a lot of links to example projects, one of which is a self-calibrating ATTiny45 USB keyboard interface. The ATTiny45 is a small 8 pin chip which just fit in the space I had available on the pen`s interface. Due to the self-calibrating code, it did not require an external crystal, which is normally needed due to frequency precision requirements of the USB interface. Basically, that project was a perfect starting poattachments_refint and someone had already done most of the work for me. Excellent! The circuit I put together is shown in the...

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