AVR Origin N3

Since I used Raspberry Pi to initially program my boards, to protect my other hardware, I designed a hat for it. This hat brings out few connectors for proper usage. Also it allows selecting between 3v and 5v power going to the chip being programmed, or turning it off alltogether. When it is turned off, one can use the terminal to feed even higher voltage power without endangering the raspi.

• I2C
• ISP
• Serial

While it is useful for protecting the computer, it is impractical because one still needs a full monitor, keyboard, and mouse to use it. Not to mention the mess of USB cables. So I will not be developing it further than this 3rd generation, but for future version one should add 5k pull up resistors for the I2C pins.

Because of the serial connector is it also possible to use serial communications to talk to the board without a proper FTDI cable. So in a tight pinch with this board, chips can be programmed without a proper dedicated programmer. Even if you are making your first ISP programmer stick. Thus the name AVR Origin.

Never really needed to use the I2C interface on this board, so I dont know if the raspi needs some specific configurations for its use aside from activating them from the raspi configuration. For serial communications the same applies, altough with Raspberry Pi Zero W, you might get overlap with the inbuilt wifi and need to look into swapping the bluetooth and wifi serial interfaces around. That way you can disable the bluetooth while still having proper network connectivity.

To use the ISP programming takes bit more work, the raspberry has the pins for it, and avrdude has linuxgpio support that allows it to use them. You just need to compile the avrdude yourself to implement the feature. Raspberry PI, linuxgpio - AVRdude Install

Altough this hat has been designed for the raspberry pi zero formfactor, the 2x20 connector is compatitible with all modern raspi boards.

On my AVR Origin board, as I like to call it, I have also taken advantage of the fact that raspi gives out both 3,3v and 5v, so it was matter of simply adding a switch to allow switching in between the voltages. I also added an extra switch on the long side, that allows me to cut power alltogether to the chip being programmed. While so far it has been unnnecessary I included a screw terminal as power out, or if the main switch for the power is off it can be used as a power input for boards that need more power.

the one component the hat needs, that is not in the lab inventory, is the 20x2 pin female connector, that is the connection to the raspi board.

When I was milling out my raspi hat, I used a 0.2mm milling bit I had found online, one of the biggest problems I had with making the board, was that the 1mm cutting bit we had at the lab for the roland mill was way too big. When ever I tried to make the holes with it, it would leave the pads so small that some of them would be ripped off the board while it was being made. So I found these 0.5mm milling bits online that were perfect for the job, and allowed the roland mill to make the right sized holes without ripping the pads off.

While the engraving bits are officially 0.1mm at their tip, when cutting 0.1mm deep into a circuit board to make the traces, the effective width is nearly perfectly 0.2mm. Allowing me to make some very beautiful cuts. The cost of them is not probhitive. If I had bought engraving bits with 10 degree tip, the effective cutting width would have been the 0.1mm.