4B: Barometer

Make sure that your CoDrone Mini is paired before starting the lesson! If you forgot how to do this, make sure to review how to pair to Blockly here.

You have probably felt the effects of changing air pressure before if you have been on an airplane or on a road trip through the mountains. As you climb higher and higher the air pressure decreases very quickly. The same thing happens if you are driving down the mountain or descending in an airplane. These changes in pressure cause your ears to pop!

If you have trouble remembering air pressure decreases as you go up higher, think of a swimming pool. The deeper you go to the bottom surface of the pool, the more pressure you feel. Now just replace water with air! The closer you are to the surface of the Earth (like sea level) the more air is “pushing” down on us.

The function to read air pressure is called get_pressure(). Connect it to a print block and see what the number says. What do you think it means?

The units of air pressure are in Pascals. 1 pascal is equal to approximately 0.000145 pounds per square inch. Use this information to calculate how many points per square inch of pressure is in your area, then compare this value to the weather data of your city. You can search “barometric pressure”. Units are normally given in “inches of mercury” so you will need to convert it to Pascals to compare!

Practice saving air pressure to a variable and printing the variable value. Make sure you use a descriptive name for your variables.

Since you can’t take your CoDrone Mini up to the top of Mount Everest and measure changes in the air pressure, you can do a quick experiment at home using a snack bag! 

First, take a pressure reading for your base reading. Then, get a plastic Ziploc bag and put your CDM inside. Make sure it has a little bit of air inside! Then, write code to take multiple readings using a repeat block. Press down on the bag to see the air pressure change. Does it increase or decrease? Why do you think?

After your experiment, analyze the data. Find out where the air pressure was the highest and where it was the lowest. Then, brainstorm different ways to increase the pressure without breaking your bag or your CoDrone Mini!

Now that you can observe changes in air pressure, you are going to code a program that warns you if the pressure changes! You have probably seen these types of sensors in action in car tires.  If the tire pressure is low, it wears out the tires and makes it unsafe to drive.

Let’s replicate this sensor with your drone. First, find out what the normal pressure value is inside the bag. Assign this value to a variable. Then, use a repeat block to continuously check the air pressure. Include an if statement that checks if the air pressure increases above the starting value. If so, change the LED to red. Else, the LED should be green.

To see how much the pressure changes during flight, you will take measurements and compare the values at different times during the flight. Print out the pressure at ground level, after takeoff, and after throttling up two times. By how much does the pressure change? Will it increase or decrease? Why?

Since air pressure changes with altitude, the barometer can also be used to estimate height. 

Try printing out the height in a repeat block while slowly moving CDM up and down. What value does it start at? 

All devices will have some level of inaccuracy. Test how accurate the barometer is at estimating the height off of the ground. 

Use a loop to throttle up three times equal distances and take three height measurements. Are the differences in height relatively equal?

Now, take a height measurement immediately after taking off. Then, throttle up until your height reaches the initial height + 30 (centimeters). Take another reading right before landing to confirm that your code worked. The difference in values should be 30 units.