Wednesday, December 25, 2013

Ion Chamber

NearSys is experimenting with ion chambers as an affordable radiation detector for robots and near space. The designs under experiment can be found at Charles Wenzel's website,

The electronics are soldered to a perf board and shielded with a copper pipe cap. The electronics are bolted to the can of the chamber, making the ion chamber a very durable unit.

Currently, the ion chamber under study is being read by the READADC command. to my surprise, I have determined that 5.5 MeV alphas from Americiunm-241 can be detected by the chamber but not 4.5 MeV alphas from Uranium-238

Friday, December 20, 2013

LED-based Color Detector

NearSys is testing an application based on the work of Forest Mims. In thre early 1990's. Mr. Mims published on an interesting effect, LEDs produce current when exposed to light, mosrt especially when the light has the color that the LED produces. The reason this happens is because LEDs are like little solar cells.

So after experimenting with using LEDs as a near space photometer for several years, NearSys is now experimenting with using them in a robotics application. In this case, the unit contains two different color LEDs for detecting and two fo the same color LEDs for a light source.

A two LED color detector being tested on red-colored floor

A robot controller using this unit measures the voltage produced by both LEDs to determine the color being illiminated. The best comparison seems to be made by multiplying the two values. A red and green seems to be most effective at distinguishing between colors as the graph below illustrates.

It also appears that two infrared LEDs, one 870 nm and the other 940 nm are effective at distinguishing between gloss black and flat black surfaces.

Look for a short article about this new color detector and a YouTube video in the near future.

Here's a reference for Mr. Mims' original article

Mims III, Forrest M. "Sun Photometer with Light-emitting diodes as spectrally selective detectors" Applied Optics. Vol. 31, No. 33. November 20, 1992.

Animated LED Display

The new NearSys Animated LED Display showing the number 9

NearSys is developing a animated display of 64 (8 by 8) bicolor LEDs.

The LED array is a BL-M12A883XX from Adafruit. Each square contains two LEDs, colored red and green. both LEDs can be illuminated simulataneously, so each pixel can be off, red, green, or yellow.

A PICAXE 28X2 controls the display and receives a command for the specfic display form the robot controller it is connected to.

Setting the color of each cell in a column is easy, just set two 1-byte variables (one for red and one for green). For example,
Green = 255
Red = 255

Then increment the current column to display with thess commands
Counter = Counter + 1
Column = Counter *4

Finally, set the PICAXE-28X2 output pins to acitivate all the cells in the current row.
pinsA = Row
pinsB = Red
pinsC = Green

Current, I am testing a display for a count down timer. When completed, I'll post a YouTube video.

I will write a short article on it for Servo. look for the kit to become available at around that time (January 2014).