This is a small hardware + software system intended for measuring lap time of line follower robots. The hardware is built from common computer mouse and optical light beam sensor in a way where sensor is simulating left mouse button press. When the robot blocks the light beam, the mouse left button is pressed down and if the light beam is freed again the button is released. The software measures the time between mouse button presses. It is important not to use the real computer mouse during the measuring period, but it is possible to test the software with real mouse.

Receiver eletronics

Receiver assembled

Transmitter assembled

Components for electronics:

• Any USB computer mouse
• 5 x 2 cm PCB prototyping board
• Hamamatsu S4282-51 light modulation photo IC
• Any bright red LED
• 10uF 6,3V capacitor
• 100nF capacitor
• 15r resistor (you can even skip it)
• Two RCA (or BNC) plugs and receptables
• ~1m of two wire cable
• Plastic pipe for forming the arc for cable
• Velleman VTMG12 10x magnifier
• Two boxes
• Hot glue

Assembly instructions:

1. Disassemble the USB mouse, remove the left button switch
2. Solder the photo sensor and capacitors on the prototyping PCB
3. Connect the sensor PCB to the mouse PCB (by soldering or glueing)
4. Solder the power and signal wires between sensor and mouse PCB-s (you need to study the mouse schematics)
5. Make holes into receiver box for RCA receptable and USB cable
6. Fit the RCA receptable and solder the wires from it to the sensor PCB
7. Make a hole for lens into receiver box
8. Prepare a place in receiver box for sensor board which can be adjusted to the focal point of the lens
9. Make holes into transmitter box for LED and RCA receptable
10. Fit and solder the LED, resistor and RCA receptable in transmitter box
11. Make a wire with RCA plugs and connect it between receiver and transmitter
12. Double check schematics and plug the mouse cable to the PC
13. The transmitter LED should light up
14. Darken the room and see how the light falls onto the photo sensor through receiver lens
15. Adjust the position of the sensor board so the light spot covers the hole sensor package
16. Fix the sensor board by glueing
17. Close the boxes
18. Test the system with timer software

Screenshot of timer working

The software is written in Visual Studio 2009 C# and released under GPL licence. It's a very simple program with open source code so there's not much to describe. To start measuring lap times, press the start button in the window, press enter key on keyboard or press middle mouse button. To end measuring, press the escape key on keyboard or the right mouse button. Keep the program focused while measuring and don't move or press the left mouse button on real mouse.

The timer software window is always on top so it can overlay the Excel competition table. In the competition table, every robot have three trials among which the best time is chosen.

• Program + Source code v0.5
• Competition holding Excel table

• Mikk Leini