tcatm/lichtsensor

Abstract

A simple USB light detector consisting of a simple circuit based on an ATtiny44 and a LED. Readings are accomplished by running a userspace tool on the host. Each run will return the most recent measurement.

Measurements

Measured values will be within 0…4294967295 (32 bit value), with 0 meaning "pretty bright" and higher values meaning "less light".

Sample Readings

Value	Environment
8…15	average desk lamp
30.000…60.000	clouded sky
> 800.000	sensor hidden in a drawer

Compiling the source

Firmware

Run make within the avr directory. Make sure to the the fuses to "External Crystal" and disable CLKDIV8 (see avr/fuses for the values I used).

Client

The sample client is a single file. You'll need libusb to compile it. Usually, you can just install the devel package (apt-get install libusb-dev) on Debian-like distributions.

To compile the client, just run:

gcc -o lichtsensor client/lichtsensor.c -lusb

Taking readings

Just run the lichtsensor binary after connecting the sensor:

% ./lichtsensor
18214

If you get a Operation not permitted, try running it as root and take a look at the libusb FAQ.

Schematic

Pictures

http://imgur.com/a/VfXc4

Further research

The sensor's readings are likely to drift over time as there is no compensation or calibration yet.