Sunday, June 2, 2013

Circuit Board Designed–95%


Circuit Board design with the exception of the antenna and all respective parts (except the nRF51422 which I already have in my possession) have been ordered. They should arrive Tuesday or Wednesday which will allow me to check to make sure all the parts fit the pads I’ve outlined on the board and make any needed edits. During this time I’ll design the antenna.

Currently the board is 26mm x 32mm. It might have to get wider to accommodate the antenna slightly as I do no wish to use a meander trace. I want either a trace antenna or an IFA. I might make separate board with a ceramic antenna.

I’ve been given the suggestion to include an SMP connection such that a network analyser could be used to tune the antenna. I am going to try the technique where you make the antenna too long and cut it back. I’ve read about people tuning with a basic RF spectrum analyser with this method which is cheaper for me. (RF spectrum = 200 dollars, network analyser = thousands).

I need to spend some time on the silk screen labelling. It’d be an amateur mistake not to spend more time on this as it really helps clarify what the parts are for future debugging.

Total cost of all associated parts is somewhere in the vicinity of 30 – 40 dollars. However, I’ve been quoted at prototype assembly at 70 – 90 dollars a board. More motivation to finish the reflow toaster.


  1. Hello,
    I'm an electrical engineering student from Germany and always was like: "a powermeter can't be that hard to build by my self, how come they are so expensive?"

    Keep up the good work! Are your programming files, circuit board files and so on going to be open source? I would be highly interested, since I'm a cyclist too.

    1. I wouldn't say it's hard, just a lot of work.

      I'm not 100% sure if everything will be open sourced or not. I'm aiming more at hacker friendly. Long term strain gauge installations is not something people can do at home. Reprogramming is. So I'm hoping to take an Arduino style approach. Offer the hardware (if there proves to be some demand) and let people reprogram with aftermarket firmware. It's kind of like the WRT54G router. The router works well out of the box, but some people like hacked firmware for additional features. That's more of what I'm looking at. Provide the low cost hardware, let people add features (gyro, accelerometer, other communications, etc).

  2. Looking good Keith.
    Good work at plugging away at the design.