Design a Mini Solar Tracker System

This project follows the Engineering Design Process. Confirm with your teacher if this is acceptable for your project, and review the steps before you begin.

Design Your Solar Tracker

1. If this is your first time using a micro:bit, follow the Getting Started instructions on the micro:bit website to learn how to use your micro:bit and connect it to your computer. 
2. Decide what programming language you will use for your micro:bit:
   1. If you are new to coding, we recommend using Microsoft MakeCode to program your micro:bit. MakeCode is a graphical programming language where you make computer programs using colored blocks of code instead of a text editor. The example code in this procedure uses MakeCode. We recommend following a few of the MakeCode tutorials before you proceed.
   2. You can also program your micro:bit in Python, JavaScript, and Scratch. You may prefer this approach if you already have programming experience in one of these languages. See the Let's Code page for more details.
3. Make a plan for your solar tracker system. Here are a few things to consider:
   1. Look up the maximum voltage produced by your solar panel.
      1. If your solar panel outputs less than 3.3V maximum, you can measure its voltage directly with one of your micro:bit's pins, and you can use this voltage to track the sun's direction.
      2. If your solar panel outputs more than 3.3V, you cannot measure its voltage directly with the micro:bit. You can do that using an external multimeter. Do not connect your solar panel directly to your micro:bit, or you may damage it. To track the sun, you will need to use the micro:bit's built-in light sensing capability separately from the solar panel.
   2. Many small servo motors are rated to operate at 5V but will still run at lower voltages. The 3.3V provided by the micro:bit should be enough to power an SG90 servo, but if you purchased a different servo motor, you may need an external battery pack instead.
   3. You will need to build a physical support structure for your solar tracker. Craft materials like cardboard, hot glue, and popsicle sticks work well for small solar panels and servo motors. If you purchased larger parts, you may need to use sturdier materials.
   4. There are various ways you can display your solar panel's voltage for your system.
      1. If your solar panel's voltage is too high to connect directly to the micro:bit, you can measure it using an external multimeter.
      2. If you can operate your solar tracker while it is connected to a computer, you can use the micro:bit's serial write command to print the voltage out on a computer monitor.
      3. You can use the micro:bit's built-in LED display to show scrolling text and read out the voltage.

Build Your Circuit

Assemble your circuit according to your plan. Figure 5 shows a circuit with an SG90 servo and solar panel connected directly to the micro:bit.

1. To connect the servo motor:
   1. The servo motor's cable probably ends in female pins. Plug male jumper wires into these pins so you can then connect them to alligator clips.
   2. Connect the servo motor's brown wire (ground) to the micro:bit's GND pin.
   3. Connect the servo motor's red wire (power) to the micro:bit's 3V pin.
   4. Connect the servo motor's orange wire (signal) to micro:bit pin 0.
2. To connect the solar panel (only do this if your panel outputs less than 3.3V):
   1. Use an alligator clip to connect the solar panel's black (negative) wire to the micro:bit's GND pin. Note that the pin may be too crowded to connect multiple alligator clips to it directly. Instead, you can connect the alligator clips to each other, and just connect one of them to the GND pin.
   2. Use an alligator clip to connect the solar panel's red (positive) wire to micro:bit pin 1.

Image Credit: Ben Finio / Science Buddies

Figure 5. Servo motor and solar panel connections.

3. If your servo motor requires more power than the micro:bit can provide, connect an external battery pack as shown in Figure 6. Remember that some servos rated for 5V may still work with the micro:bit's 3.3V supply, so you will need to test it to find out.
   1. Disconnect the servo motor's red (positive) wire from the micro:bit's 3V pin.
   2. Connect it to the battery pack's red (positive) wire instead.
   3. Connect the battery pack's black (negative) wire to the micro:bit's GND pin (or to another alligator clip that is already connected to the pin).

Image Credit: Ben Finio / Science Buddies

Write Your Code

Figure 7 shows an example program that you can use to get started. Watch the video tutorial for a step-by-step walkthrough of building the program. Here are some things to consider:

1. You can change the number in the change angle by 5 block to change the incremental movements when your motor system the sky searching for the sun. A smaller angle will be more accurate but will take longer.
2. The servo motor takes some time to reach its new position. While the servo is moving, it draws a lot of power. It is a good idea to have a pause command after the servo write pin P0 to value block to give the servo time to reach its new position and stop moving before you read the voltage.
3. The analog read pin P1 block will return a number between 0 and 1,023. However, this number does not have units of voltage. 0 corresponds to 0V, and 1,023 corresponds to the maximum (3.3V). You can convert from the analog read value to voltage using the equation set voltage to 3.3 × analog read pin P1 / 1023.
4. If you are using the micro:bit's built-in light sensor instead of measuring your solar panel's voltage, then you will want to delete the set voltage block. You can create a different variable called light and set it equal to the light level value under Input in the blocks menu. You will need to change the rest of your program accordingly (change max voltage to max light etc.). Note that you cannot convert this light level directly to the solar panel's voltage like you can with the analog read command.
5. You can use the serial write value blocks to write values to the serial monitor if you will be doing your tests while your micro:bit is still connected to a computer. Click the "Show data (Device)" button to see the data after you have downloaded your code. 
6. You can use the show string block under Basic in the blocks menu to show scrolling text using the micro:bit's built-in LED grid.
7. You want your solar tracking system to spend as much time as possible pointed directly at the sun - not scanning back and forth looking for the sun. The sun does not move through the sky very quickly, so you can include a long delay at the end of your forever loop using the pause (ms) block. You can make this number very large when you are ready to test outside using the sun. When you are initially testing inside (which you can do with a flashlight or lamp), you can make the delay shorter, so you do not have to sit there for long periods of time waiting for it to react to changes in light.

Image Credit: Ben Finio / Science Buddies

Figure 7. Makecode blocks for solar tracker.

Build a Support Structure

You will need to build a support structure for your solar tracking system. Figures 8 and 9 show an example. If you are using the micro:bit's built-in light sensing, it will also need to be mounted on the servo motor instead of fixed to the base.

1. The servo motor is held upright by a frame made from popsicle sticks and hot glue.
2. The solar panel is mounted to the servo motor using popsicle sticks and hot glue.
3. The servo motor and micro:bit are both attached to a piece of cardboard that serves as a base. You may want to use tape (not hot glue) to secure your micro:bit so it is more easily removable.

Image Credit: Ben Finio / Science Buddies

Figure 8. Close up of popsicle stick support structure for servo motor.

Image Credit: Ben Finio / Science Buddies

Figure 9. Servo motor and micro:bit attached to cardboard base.

Test Your Solar Tracker

1. Since the sun moves so slowly, to initially test your solar tracker, you may want to test it indoors. There are two ways to do this:
   1. Leave the cardboard base in place, and use a moveable light source like a flashlight or lamp.
   2. Rotate the cardboard base to change its orientation, and use a fixed light source like a ceiling light or window.
2. Download your code, watch the servo motor scan, and see if it turns to the position that is pointed toward the most light.
3. Move your light source (or rotate the base) and watch the motor scan again (if needed, remember to decrease the value in the pause (ms) block so you do not have to wait a long time between tests). It should point in the new direction of the brightest light source.
4. If your tracker does not work properly, here are some suggestions:
   1. Make sure none of your alligator clips are loose.
   2. Make sure the exposed metal ends of the alligator clips are not bumping into each other. This can create a short circuit. 
   3. Increase the pause (ms) value immediately after the servo write block to give the motor more time to finish moving.
   4. Make sure your servo motor works by testing this servo sweep code. This code just makes the motor oscillate back and forth continuously. If your servo still does not move at all, it may need an external battery pack as shown in Figure 6.
   5. If you are testing indoors, try to test in a room with a single bright light source or hold an artificial light source very close to the micro:bit so there is less interference from windows or other lights in the room.
5. When you are ready, set your solar tracker up outdoors to test on a sunny day.
   1. If you had previously decreased the pause ms value at the end of the forever loop, remember to increase it again before testing outside. 
   2. If there is no risk of rain, you can leave your micro:bit connected to a computer so you can print out data from the serial monitor. This also allows you to power the micro:bit with the computer's USB port.
   3. If you cannot leave a computer outside, you can still power your micro:bit using a USB cable and phone charger/wall adapter. This approach is preferable to using the 2xAAA battery pack included with your micro:bit, which may not last all day (especially if your micro:bit is powering the servo motor directly).
   4. If possible, you can set up a camera in time-lapse mode to take a video of your solar tracker system as it moves throughout the day. If this is not possible, you can come take pictures of your tracker at set intervals (for example, every 30 or 60 minutes).
6. Evaluate your solar tracker's performance. Does it always seem to follow the sun? Do you ever catch it pointing in the wrong direction? If so, can you figure out what went wrong? Are there any changes you can make to either your code or your physical setup to improve your tracker's performance? See the Variations section for more ideas.