And cheap, yes! River Falls, WI October 30, 2010 Saint Cloud State University, MN

What are photogates? Photogates measure time with millisecond accuracy. With known distance, photogate timers can calculate period, speed, angular speed, acceleration, etc. One can do Newton’s 2 nd law, conservation of momentum and energy etc. with photogates. Photogate systems are carried by all major vendors. You can DIY a commercial-quality system. You only spend a fraction of the cost.

Comparison Pasco standalone $400Vernier PC-based $150+software DIY less than $60 Works with existing gates

What you need? Parts: Arduino microcontroller development board $25 Photo interrupter modules $2 $4 total Stereo audio jacks 3.5mm $1.5 each $6 total Stereo audio cables 3.5mm $2 $4 total Headers and resistors $2.5 Prototype boards and wires $8 Or PCB (much easier to solder) $20 (cheaper with batch order) Tools: Basic PC/Mac/Linux computer with USB RadioShack soldering set $8 Cutting tools if you use prototype boards Total: $50 if you’re good with proto-boards and diagrams or $60 if you’re not

What is an Arduino? Arduino is an open-source, very easy to learn/use physical computing platform Arduino can sense many types of sensors and buttons (analog and digital) Arduino can be programmed to sense its inputs repeatedly Arduino can communicate with a computer via the serial port Arduino has an active online community

Initial tests on breadboard Breadboard testing Connections PC interface Breadboard testing Connections PC interface Breadboard testing Connections

Very simple setup It is a proof of the concept but is not student-proof!

Switching to PCB Photogate diagramPhotogate PCB Shield diagramShield PCB Arduino spacing

PCB results PCB Populated PCB Connected to photogates Arduino board

Photogate 10mm

Improvements All parts are safe and secure Soldering is a breeze Jumper wires to audio cables and stereo jacks Breadboard-bound gates to standalone gates Gates can stay a few meters away from the timer and be mounted Arduino board can be easily taken out for repurposing and put back without having to connect a bunch of wires

Program the Arduino Open Arduino environment and load source code Compile source code Download compiled code to Arduino board

The PC program Shows live data Options of different measurements Save data automatically

Videos

How long does it take? Programming the microcontroller – 30s Soldering the PCB – 20 min Or using proto-board – 60 min? (I did the easy way) Running data collection – 30s Securing photogates – depends on your setup Testing everything – 10 min

What do you get? You will get one timer You will get two gates Same functionality is sold for $400 at Pasco Your system is pin-compatible with Pasco or Daedalon gates (needs ¼” to 3.5mm converter $2) You’re very happy You’ll likely make more stuff with the Arduino board Who knows? World peace?

How accurate is it? Well, it depends on three things: your picket fence, the timing accuracy and the speed being measured. The PC serial limits dt to ~0.1ms timing for two gates Say you use 1.00±0.01cm picket fence machined with a mill. For 1.00m/s speed, you get 1.4%. Boring math:

Update: Physics shield Connectors: Proto-connector Breadboard connector Stereo plug connector Compatible with all Arduino boards Two robust RJ11 connectors for sensors LCD and 6 buttons for user interaction GPS connector for GPS applications Real time clock and EEPROM for data logging, timing etc. Brings out all Arduino pins Photogate connector

Future directions: More functions on the PC photogate program Support more gates (may reduce timing accuracy) Start a blog liudr.wordpress.com for physics projects Develop more shields for physics prototyping Develop upper-division electronics class with Arduino

Thank you!

Care for some details?

Just links Arduino official site Arduino forum My blog Programs for the photogate shield (on my blog) Parts: Arduino microcontroller development board Arduino microcontroller development board $25 Photo interrupter modules Photo interrupter modules $2 $4 total Stereo audio jacks 3.5mm Stereo audio jacks 3.5mm $1.5 each $6 total Stereo audio cables 3.5mm Stereo audio cables 3.5mm $2 $4 total Headers and resistors Headers and resistors $2.5 Prototype boards and wiresPrototype boards and wires $8 Phi-1 shield (please check my blog)