Matt Todd, Max Beard, and Kyle Roberts are three Mechanical Engineering students from Colorado State University who have designed a portable weather station.
The Portable Electronic Weather Evaluator (PEWE) is equipped with multiple sensors: a barometric pressure sensor; an anemometer for measuring wind speed; an altitude sensor; and a thermistor to measure the change in temperature. On the PEWE's front panel, as seen in Figure 2, there are 10 LED's along the right side that light up proportionally to measure the wind speed as well as another 10 LED's that correspond proportionally to measure the temperature. There are also two LCD displays. The top LCD displays all of the sensors readings. The bottom LCD displays a logic statement corresponding to the sensors readings as well as the PEWE's introduction when the device is turned on. Below the LCD's are five LED's that, from left to right, display high temperature, low temperature, high altitude, high wind, and low pressure. These LEDs also correspond to logic statements that are displayed on the bottom LCD screen.
Matt, Max, and Kyle with the PEWE
Under the 5 LED's, there is a row of four buttons. The two left most buttons control the raising and lowering of the anemometer. The two right most buttons control the SOS function and the light show. When the SOS button is pressed, the LEDs that surround the anemometer housing flash SOS in Morse code. Under these four buttons, there are two additional buttons that control the sound and the unit conversions. The user can switch between metric and SAE units as well as turn the buzzer on and off. PEWE has two power switches at the bottom of the front panel. The left most power switch is wired to a 9V battery which powers the Arduino. The right most power switch is also wired to a 9V battery that turns on the power to the driver board and supplies a 5V power source to the PIC16F88.
Figure 2: Description of the PEWE
As seen in Figure 2, the housing for the anemometer sits on top of the PEWE. The anemometer sits on top of a 3-D printed riser which is attached to a lead screw by the use of a journal bearing. The lead screw and two stabilizing rods are used to convert the rotary motion of the NEMA 17 stepper motor to linear motion, as seen in Figure 4. This motion is used to raise and lower the anemometer. The stepper motor is controlled by a PIC microcontroller and an 'easy driver board.' The PIC tells the driver board which direction to turn the motor as well as sends pulses to the driver board which correspond to the amount of steps the stepper motor takes. The lead screw pitch has 12 threads per inch. The anemometer needed to be raised 3 inches therefore the stepper motor had to precisely controllable to make 36 rotations.
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Hi, armorris, Charlieplexing is a method of addressing more LEDs with fewer pins. Charliplexing is named after Charlie Allen of Maxim. It uses the tri-state property of I/O pins, i.e., High, Low, Input (high impedance). There are a number of explanations of the technique online. Using the technique one can address n2-n LEDs using n pins. One does have to be careful of current limitations. Another advantage of Charlieplexing is that it reduces the number of current limiting resistors, assuming all LEDs are of equal current. This would save parts count and board space. I notice that they use several resistor arrays. One should be careful on the SOS function in that driving all LEDs at once could overload the maximum total current of the MCU.
BRedmond, I just clicked on Post Message below any other message post and it worked for me in posting a new subject. Were you logged in at the time? I was looking at their code and it seems like they define THERMISTORNOMINAL as 10,000 ohms and assume that it represents 25ºC. Then they do an analog read on the thermistor pin and use the Steinhart-hart equation to calculate the temperature.
Very nice design, well documented, but experimenter socket-board is not suitable for long term use, as explained by others. I've seen many other GF projects that were built up like a permanent project, but using socket-board for the electronics. Makes no sense to me. I always use perfboard on my one-off projects. I save my (much more expensive) socketboard for breadboards only.
BTW, what is Charlieplexing? I've been a practicing electrical engineer for decades and I have never heard of it before now. Is that some kind of kludged-up multiplexing technique to save I/O pins? If that's the case, I have done it many times without knowing what it's called. Who is Charlie?
I don't understand whyI can't initiate a comment, only reply to other people's comments.
I also can't cut and paste from the article while writing my post. d'Oh!
a thermistor to measure the change in temperature and LEDs to display temperatures.
Are they measuring T or delta T? I know that Mechanical Engineers are more often interested in delta T but it seems like a weather station is more interested in the actual temperature (unless you really do want to know that the temperature has dropped 20 degrees in the last hour).
You raise good points. Breadboarding is great for prototyping. I agree that if you want to haul this into the wilderness (like where I live) you would want solder connections. But Schmartboard offers a solder breadboard that mimics the breadboard. You could actually solder the connections after confirming it works. You just lay it on top of your breadboard and solder at will.
I also agree with your comments about inability to weld for most of us. But one can get framework hardware from Adafruit and Sparkfun. Just a suggestion to others.
As far as code writing: That's why we need to practice modular design. Just call a function that can be re-used.
I agree that they did a good job on the packaging, but it is what I would expect from mechanical engineering students. I was surprised that they used a welded aluminum frame- not everyone has access to equipment for welding aluminum.
As for the electrical workmanship, I disagree that it was nice. They used breadboards for making connections to components. This is a quick and dirty way to make temporary connections. It can be unreliable, because wires and components can get loose and break connection. In the long term, corrosion could also kill the connections of a breadboard. Because this is a portable weather station, the potential operating environment (possible bad weather) should have been considered. There are better ways to make the connections. One is with custom PC boards, which they could have made themselves for not very much money. Another would be copper-clad vectorboard.
Charlieplexing would have been a good multiplexing technique for them to learn about, but it would have made the code writing/development and design work more labor intensive. It might have caused other problems, too. Because they didn't run out of microcontroller pins, there wasn't really a good reason to use Charlieplexing.
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