Laser Scanner Part 2: (Perimeter Mode)

Similar to the input devices assignment, I decided to try to visualize the scanner mechanism I cobbled together. The architecture is as follows:

block diagram

And here is a picture of the actual device:

Most of the components are were picked up here and there surplus. The laser range finder was designed for checking products on assembly lines (for example, measuring the height of a glass jar lid to see if it is screwed on all of the way.) The data-sheet describes measuring how many sheets of paper are in a stack, so it may be pretty accurate. The output is an analog 4-20ma current loop.

This week's progress...

All of the above is interfaced to a tiny45 (new board designed and etched. See hotplate solder below) which appears to a laptop as a custom USB HID device. The microcontroller takes commands, steps the motor, and reads the sensor -- sending the results back to the laptop.

I played around more with the HID drivers... more specifically, the software I wrote/modified last time was C based. This week I spent a block of time getting the HID device readable under Python. I also tried to improve the motor control on the microcontroller side.

I also added some code to try to massage the data and plot the output using pylab.

Results:

And here is what it thought it saw scanning a box:
Box_With_Monster

And here is a toy, and what it saw:
baby_toy

Additional Notes:

Hotplate reflow (first attempt)-- The solder kicked into liquid at about 160 degrees C It did an excellent job on the USB connector! Solderpaste was applied to the board, components were stuck on, and the whole shebang was tossed on a hotplate. Result: great joints, 1 bridge. (a nice reference: http://reprap.org/wiki/HotplateReflowTechnique.)

Reference explaining VUSB clocking on the Tiny45.: http://vusb.wikidot.com/examples (see section titled:

Clocking the AVR from the RC oscillator with auto-calibration)

USB Serial Reference Projects: http://www.obdev.at/products/vusb/avrdoper.html

TI DRV8811 Motor chips appear to have the same pinout as the Allegro chips described on the MTM schematic. They may run at reduced power, or have less operating modes.