6 Dec

Tenergy LiFePO4 CR123 Cell Test


I stumbled upon Tenergy’s lithium iron phosphate CR123 cells when looking for a fairly compact cylindrical rechargeable battery. The Tenergy RCR123A LiFePO4 cell, as listed on Tenergy’s website, supposedly has a nominal voltage of 3v and a nominal capacity of 750mAh. Both of these values seemed a bit unusual, so I ran the battery through a discharge test to get some realistic data on what this cell is capable of. Note that many consumer battery manufacturers publish capacity numbers that are more than 200% of the real-world value, so this isn’t a unique case.

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31 Oct

DIY 3D-Printed Model Rocket


3… 2… 1… Blast off!

Space has often been referred to as the final frontier, and many who look towards the heavens find themselves wondering what might be hiding just beyond our reach. Although commercial space missions cost well into the millions and even billions of dollars, model rocket enthusiasts have been striving to reach just a bit closer to space for decades. Estes model rockets have allowed generations of kids to dream about one day escaping the earth’s gravity and venturing into the unknown. I like to think that a bit of exploratory spirit can be found in everyone, and I am certainly no exception. Read more »

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19 Oct

FeatherHAB: 2-gram High Altitude Balloon Tracker

FeatherHAB Balloon Tracker

FeatherHAB is a lightweight, small, and inexpensive balloon tracker. It tracks the location of a balloon with GPS and broadcasts the balloon’s position to the APRS network on 144.390MHz. The tracker is built around a Ublox MAX8 GPS module and a custom RF transmitter designed with the Silicon Labs Si446x transceiver IC. Power is supplied by a single-cell Lithium battery, which runs through a tiny buck-boost converter to power the system. The total weight comes in at about 2 grams without a battery.

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23 Aug

Therm: a Tiny PID Controller

Therm PCB top

Therm is a very small PID controller with an OLED display, thermocouple interface, and USB port. It can switch an external solid-state relay for driving large loads, or a transistor for driving small loads. When attached to a computer, it enumerates as a USB serial port for easy control and logging of data. The design is based around a STM32F0 microcontroller and the MAX31855 thermocouple-to-digital IC (note: an RTD version of therm is in the works). Read more »

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8 Aug

Local Restaurants: The Ann Arbor Experience

Polaroid Shots of Ann Arbor

Polaroid Shots of Ann Arbor

Ann Arbor is known for its exceptional selection of local restaurants, but picking a place to try can be overwhelming. Here is a short list of my favorite places to eat in town that you won’t find anywhere else.

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Food | 1 Comment | Tags: , , , , , , , , , , , ,
31 May

The CANable: a small USB to CAN adapter


The CANable is now available for purchase on the Protofusion store!

The CANable is a hardware clone of Eric Evenchick’s CANtact project, an open-hardware USB to CAN adapter compatible with socketcan. I took his design and reworked the hardware to be a bit more suitable for my personal needs, with a screw terminal instead of a DB9 connector and a much smaller PCB.

The design is open-source hardware and the schematic is nearly identical to CANtact except CANable uses the STM32L042’s onboard high speed oscillator, has a micro-USB connector, and has a smaller 3.3v regulator. Feel free to pull down the hardware source and the firmware (a forked version of the CANtact firmware that uses the internal oscillator instead of an external crystal).

Update: CANable support has been merged into the CANtact firmware. Just change the define in main.c for CANable and you should be good to go!

I’m currently not producing these boards, but you may fabricate your own from the source files linked above. If there’s enough interest I may consider fabricating and selling some boards. Drop a comment if you’re interested!

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13 Mar

Crazyflie 2.0 Review

Crazyflie 2.0

The Crazyflie 2.0 is a second generation nano quadcopter created by Bitcraze as part of their open-source flying development platform. Available for $180 from Seeed Studio, this developer-friendly kit seemed like the perfect way to dip my toes into the increasingly popular world of hobbyist drones. I went for the developer combo package, which included the Crazyflie kit, Crazyradio, JTAG debugger, and a couple breakout/prototyping boards for $215. I also purchased a few spare batteries to extend my flight time, a decision I definitely haven’t regretted. Read more »

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1 Mar

Immersion Heating with a Vacuum Tube

A 6v6 vacuum tube heating some water

Recently I was doing some woodworking and wanted to try fuming a small test piece of oak with ammonia. The fuming process darkens the wood and gives it a nice aged, gray look. To speed the process up, I decided to heat my ammonia solution to increase the rate of evaporation. With nothing else on hand and with a desire to do something fairly ridiculous, I decided to use a vacuum tube as an immersion heater in a closed-loop PID heating setup for my ammonia fumer.

Disclaimer: This is a sub-optimal solution to this problem, don’t try this at home, ammonia vapor is poisonous, etc…

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15 Feb

Low Cost DIY Photobooth

Sample Photobooth Photostrips

Sample photobooth photostrips

Photobooths are popular at many types of social events, including weddings, birthday parties, and school dances. However, renting one can easily cost upwards of $1000, making them impractical for many events. So when a friend mentioned wanting one for her wedding, I jumped at the opportunity to build a low-cost DIY photobooth.

To make my photobooth cost-efficient, I decided to use a thermal receipt printer to print out black and white photo strips, which eliminates the need for an expensive photo printer and photo paper/ink. I also added Twitter integration so the photobooth can tweet out every photo strip it takes, and a QR code generator that prints a link to the corresponding Twitter post on each photo strip.

The BeagleBone Black single-board computer seemed like a perfect match to power this project, and I decided to script everything in Python to keep it simple. Gphoto2 provides the camera interface, CUPS handles the printing, and Python libraries take care of everything else.

Lets get into the details of how this thing works.

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Linux, Projects, Python | 2 Comments | Tags: , , , , , , , , , , , , , , ,
24 Sep

Luma Controller Development


The Luma Controller takes any audio input, calculates and analyzes a FFT of the spectrum, and sends commands out to a network of Luma nodes. This board duplicates the functionality of our music analysis software, but with greater flexibility and significantly less latency. The first prototype of the Luma controller is up and running and is built around an Arduino-bootloaded ATMEGA328. Although this board is functional and provides decent results, we are redesigning the controller from the ground up with a more powerful ARM processor.

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MNL, Projects | No Comments