Help with Arduino and Servo specifications.

Hello again. I plan on connecting a relay to the Arduino uno. But i know i have to place a transistor in between them. If i have a seperate power supply (6V) controlling a motor, and i have the relay along that power supply, would i need a 5V relay or a 12V? When buying a relay, does 5V or any voltage mean that is the voltage that flips the relay on/off? or is that the maximum voltage that the relay can handle? thanks. :smiley:

There are two main sets of ratings for a relay. One is for the coil that actuates the relay and the other is for the contacts that carry the controlled current. The coil will have ratings called pull in voltage , voltage needed to get the relay to switch, and holding current, the current that you must supply to keep the relay switched. Those are on the coil side. On the contact side are the rated voltage and current that the contacts can handle.

Ok. Thanks. Would a better decision be to just use a transistor with the Arduino? My motors are six volts so would a transistor without the relays work best?

Is the motor only going to be run in one direction? If so, probably better with a transistor. You can use PWM to control speed if using a transistor, but not with a relay. If you need forward and reverse you'll need an
H-bridge of some kind. Google "arduino dc motor control" for many many circuits and code.

i actually have four motors that are going full speed and it would be nice if i could they could be reversed. can i use one H-bridge to reverse multiple motors? the motors wont be running at the same time all the time, will this affect the h bridge?

If you somehow switch the motor leads to the H-bridge, perhaps. But it would be a lot easier to just have a bridge for each motor. I would use a 754410 chip for the bridges. Each 754410 will drive two motors. You will have independent control of speed and direction for each motor. You may need to supply a bit more voltage to the 754410 to get 6 volts to your motors as it drops some voltage. How ever you do the bridges, don't forget the flyback diodes to protect the bridge circuit from reverse voltage from the motors. The 754410 has them built in.

If you're trying to choose components to drive your motors you need to know the peak current drawn by the motor, as well as the supply voltage.

If the754410 chip already has the fly back didodes built in, then why would I need them on the breadboard? Is it just a safety measure? Thanks!
I'll check the peak current

tjrusk12:
i actually have four motors that are going full speed and it would be nice if i could they could be reversed. can i use one H-bridge to reverse multiple motors? the motors wont be running at the same time all the time, will this affect the h bridge?

It is also possible to use a double pole double throw relay and a MOSFET transistor to control speed/direction of a motor instead of an H-bridge if desired.

I haven't used external diodes for any of my 754410 drivers and have had no trouble. They are made for motor and solenoid driving so the internal diodes are sufficient. They can drive up to 1 amp.

Ok! Sounds great! So about three of the bridges and transistors will do the job? Any other required parts? :slight_smile:

I don't know what you need transistors for. Each 754410 chip will drive two motors (forward, reverse and PWM speed). You have four motors so all you should need is two chips. ( buy a few as they are handy little devils, good for stepper drivers and solenoid drivers as well as dc motors)

Ok! I thought I would need them to use as a switch. But the motor chip apparently does that? It switches on and off the motors? :slight_smile: I will get a few

Oh yes I forgot to ask, does the h bridge operate the two motors separately or at the same time? I need them to be separate

The two motors for a chip are controlled independently. The only thing that they share is motor supply voltage.

Ok! Thanks! I wil buy a couple :slight_smile:

About how large are the motor driver chips and how do I wire th chip to reverse motors?

For ease of bread boarding get DIP packages (16 pin). Google "arduino 754410 dc motor circuit" (lots of hits). Do you want speed control on all motors? Or just forward and reverse? Which Arduino do you have? It makes a difference on wiring.
If you want just fwd, rev, go and stop two arduino pins per motor. If you want the fwd, rev, go, stop, and speed then probably three pin per motor.

Ok I'll look it up. I've never heard of that so ill have to research it.
I'm getting the Arduino UNO. I only want the forward and reverse and off and on.

tjrusk12:
Ok I'll look it up. I've never heard of that so ill have to research it.
I'm getting the Arduino UNO. I only want the forward and reverse and off and on.

The title of your post says "Servo". You using motors or servos?