Hardware Reference
In-Depth Information
This figure is important to the driving electronics. In this chapter, I am using an
economical PCB purchased from eBay that uses the ULN2003A driver chip. I'll describe
the chip and the PCB in more detail later. The ULN2003A chip has a maximum drive
rating of 500 mA. But this figure must be derated by the duty cycle used and the number
of simultaneous drivers. If you computed a figure of 300 mA or more, you may need to
seek out a more powerful driver.
■
Note
In addition to stepper motors, the ULN2003a can drive lightbulbs and other loads.
Driver Circuit
Clearly, the GPIO outputs of the Raspberry Pi cannot drive a stepper motor directly.
You could build your own driver circuit (or breadboard one) using the ULN2003A chip.
I chose instead to buy a PCB from eBay for $2 (with free shipping), which provided the
advantage of four LEDs. These light when a winding is activated, which is useful for
testing. Figure
6-3
shows the schematic of the PCB that I used.
Figure 6-3.
ULN2003A PCB schematic
The PCB includes two holes that power connections can be soldered into. There are
also two pins marked (+) and (-) for a push-on connector.
Beside the power connections is a small jumper with the text
5 - 12 V
under it. This
jumper is shown as JP1 in the schematic. You'll normally want to leave the jumper
in
.
