Using SD Cards with Arduino - Record Servo Motor Movements

Bill,

I have a question about using SC Cards to record servo motor movements. I am working on a sixteen-channel servo controller. What I would like to do is build up the channels one at a time which would allow me to be able to go back and just rerecord one channel without affecting any of the other channels. What would you suggest to be able to do this? Thank You for your help.

Tim Lewis

@robomaster 

Did you mean SD cards ?

Assuming that you only need to store values 0-180 as the angle of the servo, each datum can be contained within a single byte.

So, on your SD card, use the first 2 bytes to save the count of samples stored on the card, where each sample is the full 16 bytes of servo positions.

Therefore, the address on the card of the first entry for servo N is 2+N (i.e. N bytes past the length counter). Each subsequent sample reading for that servo will be at 2+N+16 and so on.

So, for sample number S (for S=0,1,2,...) and servo number N (N=0,1,2,...,15), the address of its value on the card will be 2+16*S+N.

So, to record a value for servo you can use the command

seek(2+16*s+N);

to set the address and position for this samples servo N value and read or write from that position.

This way, you don't even have to implement your servos from 0 to 1 to 2 ... but can implement them in any order without corrupting the other values.

Yes, I meant SD Card. Thank You for your Idea I would like to try this out. I am still not sure to implement it but like to get this working.

@robomaster 

If it helps, think of it as a giant array of 16 byte arrays. The 16 bytes represent your servo values but the list extends along the SD card instead of your Arduino's memory.

So, you simulate moving to the index of the sample desired by passing over all of the 16 byte servo value lists before that sample and then go to the appropriate index of your servo in that list of 16 values.

If you always store the same number of samples, then you don't even need the 2 bytes at the start (i.e. the count of samples stored).

I am trying to combine the servo record and servo playback example code into a single code that will be using buttons to-do record, playback, stop functions. The functions are not looping. 

/*

SD Card Servo Record/Playback with Button Control
by Tim Lewis 9/23/2021
to store on SD Card One Channel Servo Data and Play it back.
using Push Buttons for Recod and Playback control.

*/

// Include libraries

#include <SPI.h>
#include <SD.h>
#include <Servo.h>

// CS pin for SD Card Module
const int chipSelect = 53;

// String to hold one line of text
String buffer;

// Analog pin for potentiometer
int analogPin = 0;
// Integer to hold potentiometer value
int val = 0;

// Create a Servo object
Servo myservo;

// Buttons Constants
const int RedBtn = 22; // Red Button 1
const int GrnBtn = 23; // Green Button 2
const int BlueBtn = 24; // Blue Button 3

void setup() {

// Buttons

pinMode(RedBtn, INPUT); // Button 1 as Input
pinMode(GrnBtn, INPUT); // Button 2 as Input
pinMode(BlueBtn, INPUT); // Button 3 as Input

digitalWrite(RedBtn, HIGH); // Pullup
digitalWrite(GrnBtn, HIGH); // Pullup
digitalWrite(BlueBtn, HIGH); // Pullup

// Open serial communications and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for native USB port only
}

Serial.print("Initializing SD card...");

// see if the card is present and can be initialized:
if (!SD.begin(chipSelect)) {
Serial.println("Card failed, or not present");
// don't do anything more:
while (1);
}
Serial.println("card initialized.");

// Attach servo on pin 14 to the servo object
myservo.attach(14);
}

void loop() {

// Button Control Code Here

if(digitalRead(RedBtn) == LOW) // If button 1 pressed Recording Console Inputs
{

Record(); // Record Function
}

if(digitalRead(GrnBtn) == LOW) // If button 2 pressed PlayBack Mode
{
Serial.println("Playing Back Servo File"); // Print "Playing Back Servo File" on Serial Monitor
Play(); // Playback Function
}

}

void Record() //Function to Record the movements of the Animatronic Servos

{
// Put Record Code Here
// while the STOP button NOT is pressed, continue looping
// while (! (digitalRead(BlueBtn) == HIGH )) // Stop Button not pressed

// make a string for assembling the data to log:
String dataString = "";

// Read pot value and append to the string
// Map to range of 0-180 for servo
val = map(analogRead(analogPin), 0, 1023, 0, 180);
dataString += String(val);

// Write to the servo
// Delay to allow servo to settle in position
myservo.write(val);
delay(15);

// open the file. note that only one file can be open at a time,
// so you have to close this one before opening another.
File dataFile = SD.open("servopos.txt", FILE_WRITE);

// if the file is available, write to it:
if (dataFile) {
dataFile.println(dataString);
dataFile.close();
// print to the serial port too:
Serial.println(dataString);
}
// if the file isn't open, pop up an error:
else {
Serial.println("error opening servopos.txt");
}

}

void Play() //Function to PlayBack the movements of the Animatronic Servos
{
Serial.println("Playing Back Record Servo Movements"); // Print "Playback" on Serial Monitor

// Put Playback Code Here to Play
// open the file. note that only one file can be open at a time,
// so you have to close this one before opening another.
File dataFile = SD.open("servopos.txt");

// If the file is available, read it
if (dataFile) {
while (dataFile.available()) {
// Write one line to buffer
buffer = dataFile.readStringUntil('\n');
// Print to serial monitor
Serial.println(buffer);
// Convert string to integer and position servo
myservo.write(buffer.toInt());
delay(15);

}
dataFile.close();
}
// if the file isn't open, pop up an error:
else {
Serial.println("error opening servopos.txt");
}

}

@robomaster

Just a quick comment on the code that may help (or may not)

1. the pins numbers look suspect for an arduino uno

2. the stop button is commented out in the record function

3. put in a few more Serial.println("Ive reached point x") in your code so you can trace at what point your program is failing you.

@byron I am running it on a Mega 2560 Board. it will not compile with them uncommented.

Posted by: @robotbuilder

while (! (digitalRead(BlueBtn) == HIGH ))

I suspect you just uncommented the statement above

Dont forget that the statements in a while loop need to be surrounded by {}

so 

while(!(digitalRead(BlueBtn) == HIGH)) {

   // your statments to execute if the condition is true

}

@byron 

Sorry,  I didn't mean to uncomment anything I just copied it into the Arduino IDE and went through it restoring the indents to show how much better it looks.  If the indents go then reading the code becomes much more difficult visually. IMHO

@robotbuilder - Sorry robotbuilder my post got addressed to the wrong robo.  Your efforts to present a readable bit of code meant I could actually read the code without going boggle eyed and could off some advice to robomaster.

I meant to tell @robomaster that he probably uncommented that bit of code without putting in some extra brackets when he said that uncommenting that bit of code meant is did not compile.

Doh! 🙄 

@robomaster 

I'd suggest that you change the pinMode commands for your buttons to INPUT_PULLUP from just INPUT. That will cause your buttons to be tied to the positive rail through internal resistors so they'll always stay HIGH until closed manually.

Also, can you please describe exactly what you mean by "The functions are not looping." It's not clear which functions you're talking about nor how they're supposed to loop.

I got the Record Function now looping and I can break out of it. But when I try to do the same thing with the Playback Function it does not break out of it. It does playback the file and then stops when it runs out of data. I can live with that but it would be nice to be able to stop it from playing back when pushing the stop button. (Blue Button)

Thank You for all your help.

Tim

@robomaster 

You only test if the blue button is down BEFORE you even open the file to be played back.

To interrupt the playback, you'll have to move the button test inside the "while (dataFile.available()) {"  section of the sketch.

For example ...

while (dataFile.available()  && digitalRead(BlueBtn)) {

That is  while there's more data on the file and the blue button is still UP ... etc