Servo Sweep. Learn to make a regular Servo move in a sweeping motion.

Transcription

1 Servo Sweep Learn to make a regular Servo move in a sweeping motion. We have seen how to control a Servo and also how to make an LED Fade on and off. This activity will teach you how to make a regular (position based) Servo move in a sweeping motion from side to side. First, we ll look at the sweep example given by Arduino and then we ll take a look at how you can modify the LED Fade code to look like a sweep. Arduino Regular (small) Servo Red Wire Black Wire White Wire 1. Connect the red black and white wires to their corresponding colors on the Servo and then connect to the Arduino as you did in Programming a Servo. The red wire connects to Vin (or 5V), the black wire connects to GND, and the white wire connects to Pin 9.

2 2. The motion we want for this Servo activity Sweep is detailed in the example of a sweep. This is an example that is already on Arduino and you can open it and use it as your own. Go to File -> Examples -> Servo -> Sweep. The example code is below.

3 Servo Sweep This example uses a for statement unlike the fade example that uses an if statement. A for statement is similar to an if statement, but behaves a bit differently. Once you enter a for statement, you stay there until it is complete (thus it is often referred to as a for loop ). The first statement: for(pos = 0; pos <= 180; pos += 1) means that if the position value = 0, then we want to increase the position value by 1 until pos = 180. Inside the brackets of the for statement are the actions that will take place, myservo.write(pos) and then delay(15). This means that our Servo will go to 1 degree, then 2 degrees, then 3 degrees, and so forth, all the way up to 180 degrees. It will pause for 15 milliseconds at each degree, which is just enough for the Servo to move one degree, before it has to move again, thus making it look like a continuous motion. The Servo moves 180 degrees for 15 milliseconds each degree which means it would take it 2700 (15 * 180) milliseconds (or 2.7 seconds) to sweep from 0 to 180 degrees. Once pos reaches 180, it moves on to the next for statement which says that we will start at 180 and decrease pos by 1 until we reach 0, each time moving the servo to the angle defined by the variable pos.

4 3. If you completed the LED Fade activity, you may have taken on my challenge of using the same type of code to control a Servo. If you haven t yet completed that challenge, go back and try it before moving on. That code may Servo have looked Sweep something like this: This code would make the small Servo move from 0 degrees to 180 degrees, moving 5 degrees at a time, and pausing for 30 milliseconds between each move, allowing the Servo to move the necessary amount before moving again. Personally, I like if statements better (I think they re a bit simpler to understand).

5 If you re having errors uploading, Servo check Sweep that you have written everything correctly and that you are connected to the right port, and then if you still need help refer to the Troubleshooting document. If your Servo isn t working, make sure all of your wires are connected properly and also that the Servo isn t broken (try testing it with a different Servo). 1. Try to make the altered Fade example do the exact same motion as the sweep code. You ll need to change the degree and the delay. 2. Use the Sweep example and alter it to make an LED fade on and off. Use the same logic of the Fade code but use the for statement of the Sweep example instead of the if statement of the Fade example. Challenge 1 Solution: Now there is a 15 millisecond wait at each degree instead of a 30 millisecond wait every 5 degrees, so the servo will make the exact same sweeping motion as it would with the sweep example.

6 Challenge 2 Solution: Servo Sweep Notice that we use the variable light instead of pos and we use the language of an LED (pinmode and analogwrite) instead of a Servo (myservo.attach and myservo.write). When connecting your circuit to make this LED Fade, be sure to attach the LED to pin 9, as stated in the setup.