circuit add-ons working well so far

We're experimenting with the FET switching and charge controller circuits that we mentioned in an earlier post.  So far, so good.

The FET switch, being pretty simple, does exactly what we thought it would do:  shut the "load" shields down.  Here's a link to the the particular setup we're using.

The charge controller we've only used for a couple of days.  I want to see how it holds up for at least a week before we commit to field use.

student skyping

Zack helping the Hixson kids with setting up the Ethernet shield.

show at the creative discovery museaum

Several youngsters took time from their fall break to put on a demo/educational booth at the Creative Discovery museum.  They set up several stations showing kids some core programming structures.  We set up an air sensor (methane- which isn't going to report much) to an xbee so kids could walk around while the radio sent data back to a laptop.  Fun evening.

Core structure: Using FET's to Control Power

As I mentioned in an earlier post, we're going to work in FET's  (mostly MOSFET's) to do some important stuff, notably to conserve power in remote locations and to regulate voltage.

For the former, a MOSFET can be used as a switch.  Below is a simple example I'll show the kids next wee: a motor powered by a separate power supply that is shut on an off by sending highs and low from an Arduino digital out pine to the gate of the MOSFET.  Signal high, MOSFET switches motor on. Signal low, motor is off.

·         The diode running parallel with the motor is sometimes called a flyback or kickback diode.  When current is shut off in a device that has a coil, like a motor or a relay, some of it will run backwards, which can possibly blow the MOSFET.  The diode routs that backwards current back to the motor, protecting the MOSFET.

·         The 10k resistor we see often in Arduino sketches.  It functions a  pulldown resistor.  It keeps the gate voltage at 0 if the Arduino output is low.  This avoids what is called a floating pin situation. We don’t want any stray voltage to the gate except when we signal it to be there with the digital out. 

a   And here's the generic code, setting the motor to go on and off at 5 second intervals. 

int motor=3;

void setup ()

{

  pinMode (motor, OUTPUT);

}

void loop ()

{

  digitalWrite (motor, HIGH);

 delay (5000);

  digitalWrite (motor, LOW);

  delay (5000);

}

If things work out, we can shut off the Vernier shield at much longer intervals, saving valuable milliamps along the way.  

      

burning in the mq 131

This ozone sensor takes a 48 hour burn in time.  I'm going to use the local air quality station to calibrate a value, courtesy of the AirNow site, which give you your local Air Quality Index, PM count, and ozone count in real time.

the "Wireless" part of our program getting started

One of our team members Zack got an Arduino Ethernet Shield going-  just a bit of data going to an IP address- in this case, an air sensor that we were playing with .  One small step......

How to keep the power going on our remote stations

Certainly a problem.  You have some choices:  include a bigger battery, change out the battery more often, reduce power consumption, and provide extra power.  We've been tinkering with solar, since that's where I have a bit of background.  Starting to look at a mini turbine as well.  Of course, on the supply end, there's going to be the need for charge controllers/voltage regulators. We just ordered some components to try building a few circuit designs.  There's commercial stuff out there, but might as well give a crack at making our own.

There's also using a switching function to shut the vernier shields on and off, which would also reduce power consumption. I've just gone through a skyping with the Hixson kids on how to measure power consumption of different loads and to get a rough estimate of total daily consumption.  Bit of ohm's law there.

What the voltage regultion and switching functions both have in common is that they feature FET's (Field Effect Transistors), which will give a good opportunity to bring in a bit of circuit fundamentals.  Don't know if I want to make it a recorded tutorial, skype it, or both.  It's now on my list, though.

Kids will have a booth at Startup Week

We're on to show off what we're doing at Chattanooga Startup Week at the Creative Discovery Museum. They came up with a plan where folks can graduate through several stations of increasing complexity through different programming structures.  We'll also try to get a weather balloon in the air with some of our calibrated sensors.  We've just found an ozone sensor (read the datasheet! that we look forward to using.
Here's a time lapse video of three of our youngsters trying to assemble it all while figuring out exactly how the stations will work, including a bit of venting of frustration.  Good job, kids.