Let's Make Robots!

Simple 4 pixel camera sensor

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.

4_pixel_camera_sensor_-_angle_of_incidence_computation.pdf122.82 KB

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Looks good in concept. I'm keen to try something similar to emulate an insect compound eye. What is the part number of the pin diodes?

Also where does the lens come from?

I bought the photo diodes on taobao. It seems it's a Chinese spinoff of the SFH206K. Here is a list of pin photo diodes from Hamamatsu: http://www.hamamatsu.com/us/en/product/alpha/P/4103/index.html

You can also use a BPW34.

The lens is from a broken monitoring camera.