RFarmer v0.1

A project log for NANDfarm => RFarmer

Small, easy to use, cheap ZigBee developement board for the internet of things.

Radu ConstantinRadu Constantin 07/23/2014 at 15:580 Comments

As with every first version of a project, you are bound to find errors and problems. And I had a lot. Thinking back on it I can not imagine why I sent the board to the fab. This being said, I present to you my shameful first attempt at board manufacturing with the hope that maybe some people will learn from my mistakes.

The ideea was to start the prototyping process as cheap as possible. So first of all, I started ordering samples and after a few mishaps with the postal service here, I finally had some chips to work with.  So I fired up Eagle and started to work on the schematic. After a few hours of work I was happy with the look of the board (at that time) and I started working out the prices and the aquirement of the component.

As anyone can see, there are a lot of problems with my design. First of all I did not put separate pins for device programming. So I had to connect all the necessary lines direcly to the PORTB headers. This worked for all the connections axept for the RESET. Luckily out of habbit I made the via holes for home PCB production (0.6 mm) and I was able to fit a small pin in them. 

In my hurry to finish the design I completly forgot the basic rules for differential traces and impedance matching. I am ashamed. However, with the help of a good friend, and a Network Annalyzer from the electronics laboratory I managed to barely match the circuit which resulted in a whopping 10 cm of wireless range. I am still surprised it worked at all. 

Aside from all the problems I had with this board, I am quite happy with the robustness of the small microcontroller. The single-chip sollution performed excellent even with all the short circuits bad connections, QFN hand soldering and impedance missmatching.