Nuts and Volts - May/June 2018

understand the code and makes programming, running, and debugging easier. The goal is to lower the cognitive load and have fun, of course!

Lever Up with Steppers

QI have some levers in an elevated location, and I was thinking of using a stepper motor to control them. I want to control the motor manually, i.e., rotate clockwise while I observe, stop; no computer connection.

Maybe make another adjustment a half hour later, etc.

What motors and controller should I use?

G. Alldren

AStepper motors come in many sizes and shapes, accuracies, step resolutions, and even phases. It will be hard to make a real recommendation without knowing the specific requirements. Some hobbyist suppliers have steppers and controllers available.

Adafruit is one of my favorite suppliers of such things. They also have great tutorials to get you started. There’s a nice 12V/200 steps per revolution motor available fairly cheaply at https://www.adafruit.com/product/324. The torque is 1.6 kg-cm, which is not too shabby. It has two sets of windings requiring 350 mA. This is just a guess as what you might need, though. The size of the motor that can be controlled will depend on the controller/driver.

Next, a controller is required to power the windings.

You can build one yourself from FETs but getting one pre-made is so cheap that it’s almost not worth it — except as a learning exercise. The DRV8833 looks like a good choice with its 1.2A drive capability and dual H-bridges. It’s very compact and has built-in current limiting. You can see it on a breakout board at https://www.adafruit.com/ product/3297.

If your motor requires 1.2A or less at 2. 7 to 10.8V, this should do the job. For the motor we chose above, we’ll just run it on a little less voltage at the expense of a little torque.

There’s a great tutorial for how to wire up the driver board to the motor at https://learn.adafruit.com/ adafruit-drv8833-dc-stepper-motor-driver-breakout-board/ stepper-motor-usage.

Now, the controller above must be controlled, so to speak. There are four digital inputs to the controller board. While a small computer controller like an Arduino is ideal, they can be controlled manually with a pair of switches.

It might be a bit tedious to get the motor to step, but it is possible. The motor we chose is a bipolar stepper, so we wire the four winding wires appropriately to the controller.

We can make a pair of transistor inverters that take some of the complexity out of the control. Since two of the four control wires are always inversions of each other, we’ll let the transistors do the work and then can use a simple stepping sequence. If we reverse the sequence, the motor should step in the opposite direction.

First, look at Figure 2 to see the add-ons for the controller. Note connections to AIN1, AIN2, BIN1, and BIN2.

Figure 3 shows the stepping sequence. Two toggle switches are used to set the wires high and low as appropriate. If you want to do this with an Arduino, there is a stepper motor control library that will do all this as if by magic. You’ll find it at https://www. arduino.cc/en/Reference/Stepper. NV