Simple debounce coding

Question

am a complete beginner at coding with Arduino, although I have used them for a few years by copying other peoples code. I only understand a tiny fraction of the layout of a sketch and would really appreciate some help to solve, what I believe, is a simple problem.

I have a sketch to control the speed and direction of a stepper motor:-

/*
 Stepper Motor Test
 stepper-test01.ino
 Uses MA860H or similar Stepper Driver Unit
 Has speed control & reverse switch
 
 DroneBot Workshop 2019
 https://dronebotworkshop.com
*/
 
// Defin pins
 
int reverseSwitch = 2; // Push button for reverse
int driverPUL = 7; // PUL- pin
int driverDIR = 6; // DIR- pin
int spd = A0; // Potentiometer
 
// Variables
 
int pd = 500; // Pulse Delay period
boolean setdir = LOW; // Set Direction
 
// Interrupt Handler
 
void revmotor (){
 
 setdir = !setdir;
 
}
 
 
void setup() {
 pinMode(LED_BUILTIN, OUTPUT);
 pinMode (driverPUL, OUTPUT);
 pinMode (driverDIR, OUTPUT);
 attachInterrupt(digitalPinToInterrupt(reverseSwitch), revmotor, FALLING);
 
}
 
void loop() {
 
 pd = map((analogRead(spd)),0,1023,1000,150);
 digitalWrite(driverDIR,setdir);
 digitalWrite(driverPUL,HIGH);
 digitalWrite(LED_BUILTIN, HIGH);
 delayMicroseconds(pd);
 digitalWrite(driverPUL,LOW);
 delayMicroseconds(pd);
 
}

This works perfectly with my stepper driver and stepper motor with good speed control. However, the author did warn that debounce might be a problem and this has proved to be the case. I understand the principal of debounce and I have studied a number of debounce sketches and can also understand the method of reduction using a few milliseconds delay. I believe that the following code is as simple as it can get but I have no idea how to incorporate this in the above sketch.

bool debounce() {
 static uint16_t state = 0;
 state = (state<<1) | digitalRead(btn) | 0xfe00;
 return (state == 0xff00);
}

(The author appears to have split the code into two parts (I think)

#define btn 2 //assuming we use D2 on Arduino
void setup() {
 pinMode(btn, INPUT_PULLUP);
 pinMode(LED_BUILTIN, OUTPUT);
}
void loop() {
 if (debounce()) {
 digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
 }
}

Can anyone look at these sketches and advise me if a) they are compatible and b) how do incorporate the debounce code into the working sketch?

Thanks in advance from a complete coding numptee (Scottish expression!)

• jsotola: what's the purpose of digitalWrite(LED_BUILTIN, HIGH); in the first code? ... it makes no sense to execute it repeatedly
• jsotola: The author appears to have split the code into two parts ... the author used a function ... it is grouping code into sections that are more easily managed
• Edgar Bonet: There are some simple to use debouncing libraries out there. I suggest you just use one of these instead of coding the debounce logic yourself.
• Solmod: My apologies, I was trying to use the digital write for the internal LED to see if I could spot when a transition from Hi to Lo took place. Thank you fpr pointing out that the author has used a function, but at my level of learning that still does not mean anything to me. Please be aware - I am a total novice at coding. This is why I am looking to you guys for help. Give me block of aluminium and I weill machine the most intricate device you want but show me an Arduino sketch and my brain does not compute.
• Solmod: Edgar Bonet - I'm aware that there are simple debounce libraries out there but I don't even know how to add a library to the simple code that I have working. Also, I cannot define a "simple" debounce library from a complicated one, hence why I need help.

Answer 1

You can try replacing the function revmotor() with this code. That is instead of using the separate debounce code that you have found. It works by locking out presses of the switch for 100ms following the last press.

void revmotor (){
 static uint32_t lastSwitchAtMs = 0 ;
 if ( millis() - lastSwitchAtMs > 100UL ) { // debounce 100ms
 setdir = !setdir; 
 }
 lastSwitchAtMs = millis() ; 
}

Note that the variable setdir should really be declared so volatile boolean setdir = LOW; // Set Direction

EDIT:

Incidentally, found the article that you followed here: https://dronebotworkshop.com/big-stepper-motors/ which includes the code and a schematic diagram.

• Solmod: This has worked perfectly. Thank you. I have tweaked the debounce delay up to 400 millis which works best with the switch that I am using. Thanks again.
• 6v6gt: @Solmod 400ms ? That must be some rough old switch but, anyway, I am happy that you have something which you can use. The code I supplied is a special case because it is not so usual to use an interrupt service routine to read a switch/button (overkill or sledgehammer to crack a nut) but there are cases where it is valid for example when the loop contains some blocking code.
• Solmod: The "switch" is actually the bare end of two wires at the moment until I could get everything working. Now that it works, I will be building up the physical circuit in a control box with a good quality press button switch - I may be able to reduce the period after that ;-). Anyway, thank you for you assistance - it has helped me a lot.

Answer 2

I believe that the debounce() function and example was from me that I described in my blog post The simplest button debounce solution, in fact I was not the one who first write it, I adapted it from Jack Gansslle's A Guide to Debouncing - Part 2 that was first published way back to 2004.

In your case, all you need to do is when revmotor() event is triggered, called the debounce function and alter the state of setdir only if debounce return true.

int reverseSwitch = 2; // Push button for reverse
void revmotor (){
 
 if (debounce())
 setdir = !setdir;
 
}
bool debounce() {
 static uint16_t state = 0;
 state = (state<<1) | digitalRead(reverseSwitch) | 0xfe00;
 return (state == 0xff00);
}
void setup() {
 // your pin setup code here
 pinMode(reverseSwitch, INPUT_PULLUP);
 attachInterrupt(digitalPinToInterrupt(reverseSwitch), revmotor, FALLING);
}

I must say that I did not test this particular code before post this answer, but I've been using it in similar use case in the past many times.

• Solmod: Thank you for getting involved - it is much appreciated. I have tried to follow your suggestions and I have altered my code accordingly, however, I get an error message saying "debounced" not declared in this scope. I'm not sure if I am reading this correctly but I see that the if (debounced) statement comes before the Bool debounce statement - does this have an impact on the program?
• Solmod: My code now looks like this: void revmotor (){ if (debounced()) setdir = !setdir; } bool debounce() { static uint16_t state = 0; state = (state<<1) | digitalRead(reverseSwitch) | 0xfe00; return (state == 0xff00); } void setup() { pinMode (driverPUL, OUTPUT); pinMode (driverDIR, OUTPUT); attachInterrupt(digitalPinToInterrupt(reverseSwitch), revmotor, FALLING); }
• Solmod: OK - problem solved - tiny spelling error debounce / debounced. code is running now although the debounce action is still a little erratic. I'll keep experimenting. Thank you.
• hcheung: You could change the 0xfe00 to 0x8000 and 0xff00 to 0xc000 to have longer debouncing period.
• Solmod: Thank you again for your input. For me to understand what this change will do, could you explain what the changes mean please.