Pmod HB5 Reference Manual

The Digilent Pmod HB5 (Revision E) offers a 2A H-bridge circuit to drive small to medium sized DC motors. This module was specifically designed to work with the Digilent gearbox motor which incorporates quadrature encoder feedback.

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Features

  • 2A H-bridge circuit
  • Drive a DC motor with operating voltage up to 12V
  • 6-pin JST connector for direct connection to Digilent motor/gearboxes
  • Two screw terminals for external motor power supply
  • 6-pin Pmod port with GPIO interface

Functional Description

The Pmod HB5 utilizes a full H-Bridge circuit to allow users to drive DC motors from the system board. Two sensor feedback pins are incorporated into the motor connection header and are specifically designed to work with the Digilent motor/gearbox (1:19 gear ratio) Digilent motor/gearbox (1:53 gear ratio).


Interfacing with the Pmod

The Pmod HB5 communicates with the host board via the GPIO protocol. Like all H-Bridges, care must be taken to avoid causing a potential short within the circuitry. In terms of this Pmod, this means that the Direction pin must not change state while the Enable pin is at a high voltage state. If this does occur, one set of switches that are driving the motor will be closing while the other set is opening, allowing for the possibility for both sets of switches to be open at the same time, creating a short.

To drive the motor at a specific speed, users will need to choose a static direction (provide a low voltage to the Direction pin to rotate the shaft in a clockwise direction or provide a high voltage on the Direction pin to rotate the shaft in a counter-clockwise direction) on the Direction pin, and then perform pulse width modulation on the Enable pin. The more often that the Enable pin is driven high within a set time frame, the faster the DC motor will spin.

Results from various duty cycles of the Enable pin

The way that this works is that when voltage is being applied, the motor is driven by the changing magnetic forces. When voltage is stopped, momentum causes the motor to continue spinning a while. At a high enough frequency, this process of powering and coasting enables the motor to achieve a smooth rotation that can easily be controlled through digital logic. Pmod HB5 block diagram

Pinout Description Table

Header J1 (pin 1 on the top) Header J2 (pin 1 on the bottom)
Pin Signal Description Pin Signal Description
1 DIR Direction pin 1 SB Sensor B feedback pin
2 EN Enable pin 2 SA Sensor A feedback pin
3 SA Sensor A feedback pin 3 GND Power Supply Ground
4 SB Sensor B feedback pin 4 VCC Positive Power Supply (3.3/5V)
5 GND Power Supply Ground 5 M+ Motor positive pin
6 VCC Positive Power Supply (3.3/5V) 6 M- Motor negative pin

Any external power applied to the Pmod HB5 must be within 2.7V and 5.25V; however, it is recommended that Pmod is operated at 3.3V.


Physical Dimensions

The pins on the pin header are spaced 100 mil apart. The PCB is 1.2 inches long on the sides parallel to the pins on the pin header and 0.8 inches long on the sides perpendicular to the pin header.


Additional Information

The schematics of the Pmod HB5 are available here.

Example code demonstrating how to drive and receive sensor feedback from the Pmod HB5 can be found here.

If you have any questions or comments about the Pmod HB5, feel free to post them under the appropriate section (“Add-on Boards”) of the Digilent Forum.