How to Switch a Transistor

In this video, I show how I solved my hourly hydration problem by wiring a transistor to a water pump behind my desk. I describe three different ways of switching: MOSFETs, BJTs and relays. I then skim over logic gates and show how I added lighting to my bedroom.

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The Making of the New CS120B “Intro to Embedded Systems” Parts Kit

I recently finished creating the brand new UCR CS120B Parts Kit! It took me a very long President’s Day weekend to write all the documentation, but in the end, I created a very general-purpose parts kit and produced many how-to articles Adafruit style!

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Android Phone Battery Calculations

I recently received a new Samsung Galaxy S3. Coming to Android 4.1.1 from three years of iOS is quite liberating. The phone just gives you so many more customization options and control. Amongst all the new features though, I really like the power usage meter under Settings > Battery. It presents a nice graph that shows battery charge over time and the applications using the most power. I thought it would be fun to interpret the data a bit and calculate the “full charge time” and the charge rate in mA. My calculations are below:

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Comparing PCB Manufacturer Prices: OSH Park,, iTead Studio and Upverter

For low quantities of PCBs, there are two main services available that I am aware of: OSH Park and iTead Studio. They have their pros and cons, but a new kid has come onto the block: They use OSH Park’s facility, but have a different pricing formula. I have done some analysis to find the best vendor for the project.

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Arduino-based Point-of-sales system

I made a point-of-sales system using Arduino, a receipt printer, a 20×4 LCD and a keyboard on October 13, 2012. I thought it would be a good exercise for me because I really wanted a reason to use the Adafruit receipt printer and I would have an example of an embedded systems project that was complicated enough to require a state machine. I’ve documented all the hardware and software below.

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