Hardware design decisions

A project log for Captain Pugsley - Smart motion sensor

Smart wifi connected motion tracker & iOS app with a personality!

akupilaakupila 08/14/2014 at 20:200 Comments

Captain Pugsley is a battery powered motion sensor connected using wifi. Here are some high level design decisions for the various parts. More details will follow once i've validated these things to work (still waiting for PCBs). The Rev A PCB is a 50mm diameter round PCB with everything fitting quite nicely.


Lithium polymer battery. Charging circuitry and fuel gauge on board, charging using USB or similar.


CC3000. The W23 from Atmel looks interesting but not available yet. The CC3000 has a lot of code already (yay Adafruit!) and seems great for this application. For the antenna i'm experimenting with a 2.4Ghz trace antenna (TI DN0007), we'll see how that turns out.


Initially i was considering using a raw PIR sensor and doing the amplification myself. However my analog design is pretty much as good as my French (pas très bon) i decided to go with an integrated sensor instead. Given the low volume the higher cost won't have much of an impact considering the risk of something going wrong. Panasonic's EKMC1603 turns out to be perfect. It has a digital output. The downside is that it's quite difficult to find but on the upside it comes in black and white.

Power supply

Nothing crazy here, just need to cover the power consumption of the CC3000 during transmission. Keeping everything at 3.3v lets me run of a single power rail. An LDO could work (from 3.7v LiPo) but i decided to go with a switching supply based on TPS62203D. I have plenty of board space for the inductor so size isn't an issue. We'll see how this pans out.

User interface

All configuration is done using the iPhone app. However before this it needs to connect to wifi and it'd be good to know what the status of the connection is. For this i added two leds that will shine out right next to the PIR sensor. They're connected to timer outputs so we can do some nice fading lights. During normal operation these would be off though, both to save battery life and probably more importantly not have a bit "look at me" light on the secret motion tracker..