Dc motor controll?

The most reliable way is to use limit switches in series with the motor.

Especially if damage might result in case the motor drives beyond the limit.

Not only an error in the code but also faulty transistors in the H-bridge will cause the motor to drive beyond the limit if there is no limit switch in series with the motor.

Diodes are placed across the switches to enable the motor to drive in the opposite direction when a limit switch is open.

When the transistors of the H-bridge labelled L are energized the motor will drive towards the left limit switch.

To indicate the control system the motor is at a limit, the normal open contact of the limit switch can be used. As long as the H-bridge is driven and the motor is at the limit, this contact will be positive.

If the motor hits the limit switch at full speed this will always work.

If the motor touches the limit switch at a low speed it might occur that the limit switch will open but the contact will not flip to the other side. In that case there is no indication.

For a more reliable indication an optocoupler in series with a resistor can be used across the contact of the limit switch.

The transistor of the optocoupler can be configured to create a positieve or a negative output.

Hi Johan

Thanks for that, I see how that would make it more certain.  This is just a  experiment for me to learn the programming language.  I set myself a goal and keep fighting and figuring until I have it worked out.  in the end I hope that all the bits together would be  of some use  when I make my mill table feed.

I have the switches lighting a led and when other switch is made high led switches off again.

Will try to do the same with the h bridge in1 in2 and enable next.

Once I have something a bit more complete I will post the sketch

Gerhard

Johan

While your approach is interesting, there are some cautions needed.

IN4001 thru 1N4007 are only rated at 1Amp.

You are also introducing a 0.6v drop on the motor which may be fine for higher voltages, but not for lower.

Unless you use two switches or a double pole switch, the software can't tell the limit has been reached.

The wiring to the motor needs to be significantly higher, than required for a simple switch.

This is fine for low current motors, but 5A or more will become inpractical. The switch also needs to be rated for the motor.

Unless you plan on using transistors with back emf diodes inbuilt, this design can cause issues which may destroy one of more transistors.

If the motor touches the limit switch at a low speed it might occur that the limit switch will open but the contact will not flip to the other side

The above is only applicable if you are using the limit switch to perform motor direction changing.

In Gerhards situation he is using software to determine the direction, so the switch going open is enough.

You are correct that a motor reaching the physical end is not desirable, however fusing it just below its stall current will ensure it doesn't get burnt out.

The drive mechanism should be able to handle the full stall (otherwise it becomes a liability later)

A more elegant version could include the normal limit switches to swap direction, and a second switch that cuts motor power positioned just after the limit switch.

mark

Yes Mark motor is 16A at max eff and 65A stall current and Yes I need the input from the limit switch to tell the arduino to change direction.

Also decided to leave switched with pull down resistors then I can use 1 resistor network common ground for all of then????

/* * dc moto with h-bridge and 2 potentiometers and 2 buttons * 1 button for forward at speed set by pot 1 * 2 button for bacward at speed set by pot 2 * limit switches on A4 and A5 */ /* *RS: Pin2 *E: Pin3 *D4: Pin4 *D5: Pin5 *D6: Pin6 *D7: Pin7 */ //Include Library #include //Initiate LCD object LiquidCrystal lcd(2,3,4,5,6,7); int mode1 = 28;          //switch between pin 28 int mode2 = 30;          //and pin 30 int goBut = 32;          // feed and return button pin 32 int pot1 = A0;          // potentiometer to pin A0 int pot2 = A1;          // potentiometer to pin A1 int enable = 10;      // to enable on h bridge int motorPin1 = 8;    // to In1 on h bridge int motorPin2 = 9;    // to In2 on h bride int leftBut = 24;      // button to 12 pull-down int rightBut =26;      // button to 13 pull-down int leftLimit = 11;    // limit switch to A4 int rightLimit = 12;    //limit switch to A5 int redLed = 13; void setup()                    // run once, when the sketch starts {     // Begin lcd interface:   lcd.begin(16,2);     //Print top line   lcd.clear();     Serial.begin(9600);          // set up Serial library at 9600 bps   pinMode (mode1 , INPUT);   pinMode (mode2 , INPUT);   pinMode (goBut , INPUT);   pinMode(pot1, INPUT);           pinMode(pot2,INPUT);   pinMode(enable, OUTPUT);   pinMode(motorPin1, OUTPUT);   pinMode(motorPin2, OUTPUT);   pinMode(rightBut , INPUT);   pinMode(leftBut , INPUT);   pinMode(leftLimit , INPUT);   pinMode(rightLimit , INPUT);   pinMode (redLed , INPUT);   digitalWrite (redLed , LOW);   digitalWrite (motorPin1 , LOW);   digitalWrite (motorPin2 ,LOW);   digitalWrite (enable ,LOW);   } int getSpeed1(){   int x;   x = analogRead(pot1);   x /= 10;   x = max (x , 0);   x = min (x , 100);   return x; } int getSpeed2(){   int y;   y = analogRead(pot2);   y /= 10;   y = max (y ,0);   y = min (y , 100);   return y; } int getPot1() {   int v;   v = analogRead(pot1);   v /= 4;   v = max(v, 90);   v = min(v, 255);   return v; } int getPot2() {   int w;   w = analogRead(pot2);   w /= 4;   w = max(w, 90);   w = min(w, 255);   return w; } int motorFoward() {   analogWrite(motorPin1, getPot1()); digitalWrite(enable,HIGH); digitalWrite(motorPin2,LOW); lcd.setCursor(5,1);   lcd.print("Left: ");   } int motorBackward() {   analogWrite(motorPin2, getPot2());   digitalWrite(enable,HIGH);   digitalWrite(motorPin1,LOW);   lcd.setCursor(5,1);   lcd.print("Right:");   } int allStop(){   digitalWrite (motorPin1 , LOW);   digitalWrite(motorPin2 , LOW);   digitalWrite(enable ,LOW);   lcd.setCursor(5,1);   lcd.print("Ready:");   digitalWrite(redLed , LOW); } void loop()                    // run over and over again {   lcd.setCursor(0,1);   lcd.print("  %");   lcd.setCursor(0,1);   lcd.print(getSpeed1());   lcd.setCursor(12,1);   lcd.print("  %");   lcd.setCursor(12,1);   lcd.print(getSpeed2());   delay(100);       if (digitalRead(mode1) == HIGH)   {     lcd.setCursor(0 ,0);     lcd.print("Feed mode.  ");     if (digitalRead(rightBut) == HIGH && digitalRead(leftLimit) == LOW)     {       motorFoward();     }       else if (digitalRead(leftBut) == HIGH && digitalRead(rightLimit) == LOW)     {       motorBackward();     }     else     {       allStop();     }   }   else if(digitalRead(mode2) == HIGH)   {     lcd.setCursor( 0,0);     lcd.print("Feed & Return.");     if (digitalRead(goBut) == HIGH)     {       motorFoward();     }     if (digitalRead(leftLimit) == HIGH)     {       motorBackward();     }     if (digitalRead(rightLimit) == HIGH)     {       allStop();     }         // space for the feed and return mode program        }   else   {     lcd.setCursor(0,0);     lcd.print("Select mode?");     allStop();   } }

Can Someone please exlain how to get the code to stop bundling up like this please???? something about HTML ???

Gerhard

PS  Will correct as soon as I find out how!!

Can Someone please exlain how to get the code to stop bundling up like this please???? something about HTML ???

Gerhard

PS  Will correct as soon as I find out how!!