Robot Power System

In order to construct Intel Labs Seattle’s mobile robotics platform, MARVIN, I needed to build a power system to supply the DC voltages required by the different components of the system. I used nickel-metal hydride battery packs as the battery power source and VICOR DC-DC converters to provide the various required voltages. The control panel on the rear of the robot is laser-cut acrylic and provides control over battery power, battery chargers, power to individual system components, and battery current and voltage monitoring.

One of the important features of the design is an onboard AC to DC power supply. This allows the robot to run indefinitely from a single tether, which plugs into a standard electrical outlet; no external power supply is needed. The system switches seamlessly between wall and battery power when wall power is connected or disconnected, so no part of the system needs to be shut down to connect or disconnect power. Onboard chargers enable the robot to recharge its batteries while it is plugged in.

Control panel
MARVIN’s rear control panel.  Power module controls are at the bottom.


  • Batteries: 2 13000mAh 24V Ni-MH packs in series, for 48V system power
  • DC voltage rails: 48/56V (unregulated), 24V 500W, 12V 500W, 5V 100W
  • Chargers: 2 onboard 1A Ni-MH chargers
  • Wall power supply: 110/220VAC input 56V output 1600W DC power supply, with automatic switchover
  • System runtime: 2-3 hours under normal load (arm and hand in motion, laser rangefinder and two PCs running)
  • Monitoring: Battery current and voltage meters on the back panel; soon to have computer monitoring of system voltages and currents via this board

Power module internalsInside the power module while I was constructing it. DC-DC converters and solid state relay are mounted on an aluminum side panel for heatsinking. Fuses, relays for the switching/interlock logic, and screw terminals for easy connection of peripherals are mounted on the bottom plate. Batteries will fill most of the empty space.

Classroom Presenter for the XO Laptop

UW Classroom Presenter, developed by Richard Anderson et al. at the University of Washington, is interactive presentation software that runs on tablet PCs. Each student uses his or her own tablet PC, can see written annotations made on the slide by the instructor (called “ink”) and can add his or her own ink to slides which can be submitted back to the instructor to be reviewed or shared with the class. In my undergraduate capstone project at the University of Washington, I worked with several other students to develop a version of Classroom Presenter that runs on the One Laptop Per Child foundation’s XO laptop.

The software is not just a port but a complete adaptation to make it usable on the XO. The XO is not a tablet, so only simple drawing with the trackpad (or a mouse) is possible. We added text input features to enable students to provide a textual response to a question without needing to write it with a mouse. We use the XO’s built-in facilities for discovering shared activities and connecting to other machines, so that connecting the machines together is simple enough for elementary students to do themselves. We also included features necessary for setups that don’t include a projector: the original UW Classroom Presenter expects that if the teacher wants to share a student’s submission with the class, he or she will use a projector to display it. In our implementation, we enable the teacher to broadcast selected student submissions to the rest of the class, so students may view them on their own screens.

The project culminated in a trial at a local elementary school, where students in small groups shared XO laptops to complete activities about a recent field trip, while the teacher talked about the students’ work and shared their submissions with the rest of the class.

Screenshot with student ink
Screenshot of a slide in Classroom Presenter for the XO with student responses

Students using Classroom Presenter for the XO
Students using Classroom Presenter on the XO during our classroom trial.
Photo: Mark Ahlness / CC BY-NC-ND 2.0



The results of the trial were very positive; we received great feedback both from the teacher and from his students. The source code we developed has been made available under an open source license.



In the autumn of 2004, I moved to Seattle to attend the University of Washington. I began taking photos to share some of the neat places I discovered while exploring the areas around campus with my family and friends back at home. I started with a pocket-sized point-and-shoot digital camera, back when they were starting to become popular. As I learned more about the art and science of photography, I’ve moved on to cameras and lenses that afford better manual control.

I still enjoy taking walks around the beautiful University of Washington campus on weekends and capturing some of the scenery.

Most of my earlier work is posted on my blog, Ordered Pixels. More recently, I’ve been using flickr to organize and share my photos. A few selected shots are shown below.

Artistic Photography

Sunset over the Olympics
Sunset over the Olympics. Nikon D700, Tamron 210mm f/4.0

Pink Japanese Maple
Bright Pink Japanese Maple. Nikon D70, Micro-Nikkor 55mm f/2.8

Wild Geranium and Green Bee
Wild Geranium and Green Bee. Nikon D700, Micro-Nikkor 55mm f/2.8

Hidden Hydrangea
Hidden Hydrangea. Nikon D700, Micro-Nikkor 55mm f/2.8

Helleborus. Nikon D70, Micro-Nikkor 55mm f/2.8

Autumn Leaves
Colorful Autumn Leaves. Nikon D700, Micro-Nikkor 55mm f/2.8

Orange Quad
Autumn Sunset on the UW Quad. Nikon D700, Nikkor 17-35mm f/2.8

Technical and Product Photography

In addition to my hobby photography, I often take photos of my own and others’ work at Intel Labs Seattle. My photos have been featured in various promotional materials, posters, presentations, papers, and technical documentation.

Robot Montage
Marvin the Mobile Manipulation Platform and iPhone control application. Used in promotional materials and presentations.
Nikon D700, Nikkor 50mm f/1.4

Intel WISP
Intel Wireless Identification and Sensing Platform (WISP). Used in promotional materials.
Nikon D70, Micro-Nikkor 55mm f/2.8

802.15.4 board
Prototype 802.15.4 Board. Nikon D700, Micro-Nikkor 55mm f/2.8

Power Monitor Board

Board photoAssembled power monitor board.

I designed this board to monitor the power system in Intel Labs Seattle’s mobile robotics platform. It provides four current and four voltage measurements, and interfaces with a PC via USB. Readings for all of the channels can be read at over 100 Hz.


  • Microcontroller: 8-bit AVR
  • Interfaces: USB via FTDI chip
  • Voltage measurement inputs: 4 voltage dividers using precision resistors, up to 80V
  • Current measurement inputs: 4 current sense amplifiers with 0.025Ω sense resistors (up to 4A)

Basic E-Field Sensor Board

Board photo
Basic E-Field Sensor Board. Designed for UW CSE Software for embedded systems class.

For the Winter 2009 offering of the University of Washington CSE Software for Embedded Systems course, I designed a laboratory assignment around electric field sensing. In the lab, students used an 8-bit microcontroller to accomplish the following:

  • generate a waveform at a specific frequency to drive a resonant transmitter
  • synchronously sample a received signal with an analog/digital converter
  • demodulate the received signal in software to recover the signal magnitude
  • use pulse-width modulation to drive an RGB LED, varying its color with the sensed distance between the sensor and the user’s hand

For the lab, I developed a custom PCB that contains both the transmit and receive electrodes, as well as the resonant tank for the transmitter and the analog front-end for the receiver. Header pins along the front edge of the board enabled students to plug the unit into their breadboards for connection to their microcontroller circuits. Placing the portions of the circuit that were sensitive to layout and breadboard capacitance on the PCB enabled students to focus on the objectives of the lab assignment rather than on debugging layout problems.

I designed the board to be easy to assemble; the students computed the frequencies that they would use based on the capabilities of their microcontroller and the parts available in the lab, then selected components and assembled the boards themselves. Several pads for various capacitors were provided for frequency selection.

E-field sensor board in action.