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Topic: Arduino mega with stepper, servos and a switch - seeking advice (Read 1 time) previous topic - next topic

flick

Apr 07, 2012, 08:33 pm Last Edit: Apr 07, 2012, 08:41 pm by flick Reason: 1
Hello Friends, I am trying to use a 12V 1.5A power supply to control a stepper motor, a switch and two servos as shown in the figure below (Figure 1). I am fairly confident about running the stepper motor with the 12V supply (Figure 2). However I am not sure how to use the same power supply to run the two 6V servos without frying any of the hardware. Also I plan to use the switch to stop/start the motor. I'd greatly appreciate any hints/tutorial links as to how to wire the servos and the switch to the arduino and power supply. Would I need resistors to bring down the voltage for the servos?

Figure 1: Not sure how to connect the 6V servos and switch to the Arduino and 12V supply


Figure 2: I am fairly confident about connecting the stepper motor from the schematic below


Thanks,
Flick

Nick Gammon

I don't think the resistors will work, they'll just get hot, and won't regulate properly anyway. Subject to what more experienced people might advise, I would be looking at a servo driver board connected up to a 6V supply.

Something like this:

http://www.ladyada.net/make/mshield/
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

jwatte

Most servos run fine on 5V, with only slight torque drop.

You could try running the +5V and Gnd from the Easy Driver board to the Arduino +5V and GND for powering the Arduino. However, I don't know how much current that 5V will manage to provide.

In fact, I'm not sure 1.5A is enough for one stepper and two servos. Bigger servos, when stalled, easily draw 1 amp each. Add 0.3-0.6 amps for the stepper, and you should be using a 3A supply.

What I would do is build a 6V/3A supply for the servos using an adjustable LM350 regulator, two resistors, and two capacitors. Feed it 12V, and feed its output to the servo power. Feed the Arduino only from the 5V on the Easy Driver board. I'd also use a 12V/3A power supply for that setup.
http://www.ti.com/lit/ds/snvs772a/snvs772a.pdf

zoomkat

Quote
2). However I am not sure how to use the same power supply to run the two 6V servos without frying any of the hardware.


To power servos you can use a 7805 regulator chip with a small diode connected to the 7805 ground (see below) to up the 7805 output voltage to ~5.7v for better servo performance.

Google forum search: Use Google Advanced Search and use Http://forum.arduino.cc/index in the "site or domain:" box.

flick

Thank you all for the helpful feedback. I'll head back to the store for some more shopping and get to work. Trying to wire things for the first time is like trying to defuse a bomb in an action movie climax. :smiley-roll-sweat:

flick

Hi Zoomkat, I put together the circuit for the servos/stepper/switch below. It is still not clear to me from your drawing how the other capacitor, resistors, and diodes fit in. I would greatly appreciate if you can provide feedback or possibly sketch the components on the drawing below. 



Thanks,
Flick

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