Control servo with keyboard or other hardware buttons? - c

Question

I have just gotten started with Arduino and barely have any idea about more of the advanced stuff. It seems pretty straightforward. Now I'm one who usually likes to integrate two devices together, so i was wondering if i could control a servo with the computer's keyboard or two hardware push buttons attached to the Arduino board.
In case it helps, I'm using an Arduino Uno board. Here is the example code i am using to sweep the servo for now
// Sweep
// by BARRAGAN <http://barraganstudio.com>
// This example code is in the public domain.
#include <Servo.h>
Servo myservo; // create servo object to control a servo
// a maximum of eight servo objects can be created
int pos = 0; // variable to store the servo position
void setup()
{
myservo.attach(11); // attaches the servo on pin 9 to the servo object
}
void loop()
{
for(pos = 0; pos < 45; pos += 1) // goes from 0 degrees to 180 degrees
{ // in steps of 1 degree
myservo.write(pos); // tell servo to go to position in variable 'pos'
delay(10); // waits 15ms for the servo to reach the position
}
for(pos = 45; pos>=1; pos-=1) // goes from 180 degrees to 0 degrees
{
myservo.write(pos); // tell servo to go to position in variable 'pos'
delay(10); // waits 15ms for the servo to reach the position
}
}
Now, let's say I wanted to change the servo's angle via pressing the
left/right arrow keys on my computer's keyboard. How would i go
about doing that?
Alternatively, what if i attached two push buttons to the Arduino,
and pressing one would move the servo either left or right depending
on the the button. Which ports would i plug the buttons into? Any
code samples or diagrams would greatly help!

Answer 1

To move a servo attached to an arduino attached to a computer you will need two components.
You will need software on your computer to accept keyboard commands and send commands to the arduino via the serial port. I would recommend a language like python or java to do that as a simple app can written quite easily.
Check this playground link for an example of using Java. And for an example in python check out this project.
There is a bug/feature built into the arduino that will give you grief as you go on here. The arduino is designed to auto reset when a serial connection is made to it via usb. This page has a detailed description of the issue and cites several ways to deal with it.
You will need to modify the sketch on the arduino to listen to the serial port and adjust the servo's position based on the commands received from your computer. Check out the python link above. It is an complete (hardware, pc software and arduino sketch) project designed to do something very similar to what you are trying to do.
I recommend you start with either component and try to get it going. As you run into problems, post your code and someone will be glad to help further.
As for the second question, adding buttons to the arduino is fairly simple. You will connect them to digital inputs. There are hundreds of examples on the web. Search for "add button to arduino" and see what you get. (lol... 1.3 million hits). Here again, try it and post specifics for more help.

Answer 2

For serial communication use putty
it is a cross platform Serial and ssh client
for the left and right arrow commands:
there are no ascii characters for arrow's: but there are utf-8;
putty or an other client sends utf-8 characters for the basic ascii characters are utf-8 and ascii exactly the same;
and the arduino reads only ascii characters;
the arduino reads
--> : 27, 91, 67
<-- : 27, 91, 68
so it is not that simple to read that.
you could use something like this
int pos = 0;
Serial.flush(); // flush all received data
while(Serial.avaialble()<3); // wait for the 3 ascii chars
if(Serial.read()==27){ // first char
if(Serial.read()==91){ //second char
switch (Serial.read()){
case 67: // Right arrow
myservo.write(++pos); // increment pos with 1 before write it
break;
case 68: // left arrow
myservo.write(--pos); // derement pos with 1 before write it
break;
case 65: // up arrow
myservo.write(++pos); // increment pos with 1 before write it
break;
case 66: // down arrow
myservo.write(--pos); // decrement pos with 1 before write it
break;
case default:
break;
}
}
}
but this is not a good solution
because of the arrow character is send in 3 bytes en when you flush it can flush the 27 so you read 91, 97, 27; and that is no valid so in doesn't work
you could write a algorithm to subtract the arrow command out of 5 ascii char's
or you can use 4 to move left and 6 to move right; which are ascii characters and in a numeric keypad are arrows drawn on those keys