[solved]newbie feasibility- controlling 12 "servos" shift registers &&-hbridge?

Projects General Guidance
1

Hi, I'm planning a project in which I control 12 water valves by using servos to, by a rubber band, squeeze plastic tubes to make them "on," or off. Besides the blinking LED's I'm pretty new to Arduino and circuit design. From what I understand, I can use two shift registers to individual control 12 servos, correct? Will I be able to do the pulse thing the servos require via the shift registers?

This would free up my Arduino to control a motor via a transistor, correct? I have read about using an hbridge to reverse the motor directions, and that I can build this with four transistors.

I have looked at a bunch of h bridge designs, and read about how it's dangerous to short them, but I still cannot figure out what is going on or how it is working for some reason. Is there also anybody who could explain this to me? I kind of get that two of the resistors I use flow in one direction, and these other two flow in an opposite direction, but I don't see how they all add up to make a circuit. When I am using either of the pair of transistors is electricity flowing through the circuit with the other transistors as well? Why is it the bottom pair of transistors that is connected to ground and not the top as well?

(I'm attaching an example of such an h-bridge as seen on robotroom.com)

Thanks for your help!

-Finley

example of hbridge from robotroom.com.png
example of hbridge from robotroom.com.png1345×771 91.7 KB

2

A much more reliable and easier approach would to use one of Pololu's servo controllers. They can handle 6-24 servos and the Maestro series, once programmed, can operate completely independently of the Arduino if desired. Pololu - RC Servo Controllers

3

Aaccording to the servo library reference, most Arduinos can directly (without extra hardware) control 12 servos.

4

Thanks everyone for the replies,

I think to keep things simple and streamlined I might purchase that maestro board to interface with the servos. Even if the Arduino Uno can do it having a dedicated board might make it easier since I am new. Can anybody explain to me how an h bridge works? Is the current actually reversing in the circuit or just at the motor? Thanks again.

5

The transistors in the h bridge are just switches. Think of them like this:

Ignore the enable and the lack of diodes for the moment. When you close high left and low right, current flows through the motor one direction. When you close high right and low left, current flows through the motor the other way, reversing motor direction.

6

Ah, that makes sense. Thank you.