Electronic – arduino – Controlling Multiple Servos

arduinoservoshift-registertransistors

I'm trying to control 8 servos (tower pro sg90 micro servo) using a shift register (74hc595) . I planned on giving the pwm and ground pins common to all the motors and then controlling vcc via the shift register. The IC by itself cannot drive the motor so I need a make an additional drive circuit to power the motors via the output pins of the shift register. I was thinking of using a simple transistor switch. What transistor would be cheapest and best to drive the servo ?. Would it be better to just use a 5V relay controlled by the shift register ?. Will the shift register provide enough current to the coils of the relay ?

I only need to control one servo at a time. Also I only have very few pins left on the arduino.

Best Answer

While you may only need to control one servo at a time, are you sure you don't need to hold all the servos, all the time?

A PWM expander will give you independent control of many PWM channels over I2C.

Related Solutions

Electronic – arduino – Sharing Clock and Data for 74HC595 and CD4021B Shift Registers

If I may answer my own question. It should work. Here's how with arduino over SPI.

void setup() {
    //Setup SPI
    SPI.begin();
    //Setup CD4021
    pinMode(CD4021_PSC_PIN9, OUTPUT);
    digitalWrite(CD4021_PSC_PIN9,HIGH);
    //Setup 74HC595
    pinMode(HC595_LATCH_PIN12, OUTPUT);
    digitalWrite(HC595_LATCH_PIN12,HIGH);
}

void loop(){
    //Shift out to 74HC595
    digitalWrite(HC595_LATCH_PIN12,LOW);
    SPI.transfer(BYTE_DATAOUT);
    digitalWrite(HC595_LATCH_PIN12,HIGH);

    //Shift in from CD4021B
    digitalWrite(CD4021_PSC_PIN9,LOW);
    BYTE_DATAIN = SPI.transfer(0x00);
    digitalWrite(CD4021_PSC_PIN9,HIGH);
}

Learned from here, from someone who has done this exact implementation before.

Using a Arduino Pro Mini to power more than 2 servos

That's not correct. There was a limit in early versions of the Servo library, but that's been removed. The Pro Mini uses the same ATMega 328p chip as a full-size arduino, so the only limitation is the number of PWM pins that are broken out. There are 6 on a Pro Mini, and the library supports up to 12 on a non-mega.

Also - note that the arduino micro is based on the ATmega32u4 chip, which means it'll behave like a Leonardo, not a standard Uno. It has 7 PWM pins.

Best Answer

Related Solutions

Electronic – arduino – Sharing Clock and Data for 74HC595 and CD4021B Shift Registers

Using a Arduino Pro Mini to power more than 2 servos

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