Simple 4 pixel camera sensor
July 28, 2013
In the following I describe a simple 4 pixel camera sensor, which can be versatilely used in robotics.
The sensor consists in general of four pin photo diodes with a relatively large photo sensitive area, arranged in a square, and an according collimator lens. Every photo diode can be thought of a quadrant of a two dimensional graph. We can use the sensor to measure the intensity of light, detect motions, track a light source in two dimensions or do basic 2-D optical flow calculations.
I am using a MCP604 op amp to convert the signal from the photo diode that produces an output current into a voltage (called transimpedance amplifier). This is implemented with a single resistor (R1) in the feedback loop of the amplifiers shown in schematic below. The capacitor (C1) provides stability for this circuits.
The output voltage is given by:
Light sensitivity and linearity are maximized in this photovoltaic mode.
I started to build the prototype, positioning and glueing the four pin photo diodes on a 14 x 14 mm black colored piece of carton:
Then I bended the photo diode leads and placed the sensor array in a 45 degrees angle in the middle of a 4 x 6 cm double side perf board:
Next I assembled the PCB mount lens holder and soldered the photo diode leads:
Finally I populated the board on the backside, using 1206 SMD capacitors and resistors and wrap wire. Only the MCP604 is a PDIP version.
Now I have to wait that the op amp arrives to test the sensor and write according programs:
Update August 5, 2013
I have attached a pdf called 4 pixel camera sensor - angle of incidence computation in the blog post, where I explain how to compute the angle of incidence.