Check this webpage for directions on making sensors for your near space flight computers. These sensors are also useful for model rocket satelites I'd be happy to add your suggestions for sensors you have flown with NearSys flight computers.
Solder the cable from the sensor to the short pins so the longer side can plug into the I/O receptacles of the flight computer. Since this is not a polarized header, it's possible to plug the headers into the I/O receptacles backwards. Generally this will not harm the sensor since the +5 volt pin is in the center. A good way to prevent this from occuring though is to color code the wires of the sensor cable. NearSys typically uses a white wire for the signal, red for +5 volts, and a black or green wire for ground (this is very similar to the color coding used for servo cables.
The easiest way to attach the sensor cable to a headers is to tin both the short pins of the header and the ends of the wires in the sensor cable. Slide heat shrink over the tinned wires and push them way down the wires so they don't accientally shrink when the wires are soldered to the header pins. Then place a tinned wire against a tinned header pin and apply a hot soldering iron to them. The solder in both will melt and fuse the wire to the header pin. Repeat this process for the remaining two wires and after the solder cools, slip the heat shrink tubing over the soldered connection and heat with a hot air gun. The connection will be plenty strong for a balloon or rocket flight.
To prevent the heat of the soldering iron from distorting the spacing and alignment of the pins in the header, you should plug the header into a receptacle while connecting a cable to it as shown above. After soldering the wires to the header, still leave it plugged into the receptacle while the heat gun shrinks the heat shrink.
The final cable will look like the one ilustrated below.
If two sensors will always fly together, then use a double row snapper header for them. The part is available from Jameco as a double row straight header, part number 117197. The organization of the pins is the same. Just remember each sensor has a unique signal but can share power and ground. An example of the cable from a double sensor is illustrated below.
Squirt a little hot glue around the exposed wires to prevent shorts and cover the unit in a piece of heat shrink tubing to create a temperature for the interior of the BalloonSat. The result will look like this (notice that a green dot was painted on the header to distinguish the ground pin of the header).
If a two wires are soldered the header and resistor, then the LM335 can be placed outside the airframe at the end of its cable. Cover the soldered connections and the LM335 in heat shrink tubing for protection. The result looks like this.
It's important to pick the best value for the fixed resistor (R-fixed). To get the maximum range of voltage out of the sensor, make the value of the fixed resistor equal to the square root of the CdS's maximum resistance times the CdS's minimum resistance. In other words, place the CdS cell in the dark and measure its resistance (this will be its maximum resistance). Then place it in full sunlight and measure its resistance again (this will be its minimum resistance). Multiply these two numbers together and then take the square root of the answer. To be more specific, you should place the CdS cell in the darkest light you expect it to be exposed to and then in the brightest light you expect it to be exposed to. But it will be enough that we just use sunlight and darkness.
Now you'll never get a fixed resistor with a value you just calculated, so pick one that is close to your calculated value. Then create the light sensor by soldering three wirers to the three pin header. Solder the signal wire (white) to one lead of the CdS cell and one lead of the resistor. Solder the ground wire (green or black) to the other lead of the resistor. And finally solder the +5 volt wire (red) to the other lead of the CdS cell. Be sure to slide heat shrink over the wires before you solder the wires to leads. Also, tin the wires and leads first, place then in contact, then fuse them together by heating them with a soldering iron. Your light sensor should look like this diagram when complete.
The complete light sensor loks like this.
The light sensor will be sensitive to its pointing direction, so you may want to experiment with placing it inside a diffuser. A cheap diffuser is a ping pong ball. Either cut a small hole in it and stick the business end of the light sensor inside of it or cut the ping pong ball in half and attach it to the outside of the BalloonSat or Rock-Sat airframe.
The CdS cell needs to be mounted to the outside of the airframe and beneath the half ping pong ball. The easiest way to open up a ping pong ball (and safer than an Exacto knife) is to cut it open with a pair of cuticle scissors. Use a circule template to draw a perfect circle around the ping pong ball and cut along the line.
Probably the best way to calibrate the light sensor is to make measurements at fixed distances from a light bulb in a darkened room. Measure the distance from the light bulb and take a reading with a flight computer. Record the readings for each distance from the light bulb and enter the information into a spreadsheet. After the distance column of cells, create a new column of the distances squared. That's because light intensity falls off at the square of the distance. Next plot the distance squared readings with the flight computer readings. In essence you're plotting the light intensity against the sensor's readings. After creating the chart, create a trend line and ask the spreadsheet to generate the equation. After recoverying a flight computer carrying a light sensor, use the equation to convert the readings into light intensities.
Aware Electronics makes a great gieger counter, the RM-60. It's designed to operate off of the five volts of a serial port. You can modify an inexpensive RJ-11 phone cable and add the RM-60 to your experimental payload. Plug the RJ-11 and cable into the RM-60 and cut the cable to about one foot long. Strip back the outer insulation to expose the four wires inside. Each wire will have its own color insulation. Their color is not important, but their order is. Look at the diagram below to identify each wire in the cable and its function.
Strip the insulation from three of the wires and solder them to a three pin header as described above. Don't forget to use heat shrink tubing. If you plug the RM-60 cable into an I/O receptacle of a flight computer, you can measure the background radiation with the COUNT command like this.
SYMBOL GM = 1 'This is the I/O the RM-60 is connected to
SYMBOL RESULT = B0 'Need a byte sized variable to hold the results
COUNT GM,10000,RESULT
The complete RM-60 geiger counter should look like this.
If you have suggestions for sensors, email nearsys with the information. If it's unique enough, I'll post it on this webpage.
