Monday, October 1, 2012

V3 New Circuit Boards


As you can see above the new circuit boards have arrived from Alberta Printed Circuit Boards. These guys have some of the quickest turn around I’ve seen – you do pay for it though. I’ve designed this board to not deviate too much from the smaller circuit boards I initially built – mainly to speed development of the V3.

A previous post showed a circuit board with an atmega32u4 chip and the associated circuits to support it. Considering I do not have a reflow over I opted for the simpler approach of only supporting the analog and wireless on this PCB and leaving the regulator and micro-controller on an Arduino pro micro. You can see how I broke out the ISP to make it more convenient to program.


Both of the boards mount to this main one – one via pins and the other via surface mount. I haven’t, but I should, incorporate power planes but I consciously did not include them as the AP2 module suggests not having anything metal under the F-Antenna. I probably took this to the extreme but after the difficulties with V2 maintaining a good signal I felt this was a good choice. The analog components are very very low power, on the order of micro-amps of current draw at 3.3v and I never had issues with the little circuit boards so I’m comfortable.

The voltage divider used on V2 is replaced with a precision voltage reference, the LM4140.

This will go on a bike without too much problem but having seen the size of the “Stages” power meter I’m keen to drive the size down. This would have been a great time to know some electronic engineer who works at any of the mobile phone companies as they can pack some power into a small space.

I’m keen to use the AP2 module as the nRF51422 hasn’t become available yet. I unfortunately missed my opportunity to get a free one as I had to renew my passport (Expired on the 25th of Sept, and the Boston conference was on the 24th). So I couldn’t book tickets or sign up for the tour, and as a result I’m waiting for nuhorizons to get in the evaluation kit.

I just submitted my order for parts with Digikey just then, so maybe a new prototype by the end of the week, but likely next week some time.

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