Overview

This kit includes two dual-channel Hall effect sensor boards and two 6-pole magnetic discs that can be used to add quadrature encoding to two mini plastic gearmotors (motors and cables are not included with this kit). The encoder board senses the rotation of the magnetic disc and provides a resolution of 12 counts per revolution of the motor shaft when counting both edges of both channels. To compute the counts per revolution of the gearbox output shaft, multiply the gear ratio by 12. This compact encoder solution fits within the 11.5 mm × 22.5 mm cross section of the motors on three of the four sides, and it extends approximately 5.5 mm past the edge of the fourth side.

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The encoders include a side-entry, 6-pin male JST SH-type connector with a 1mm pitch that is compatible with our 6-pin JST SH-type cables. We also carry a version of this encoder with a top-entry connector; the following pictures show a comparison of the side-entry (left) and top-entry (right) versions:

Magnetic Encoder with Side-Entry Connector on a Mini Plastic Gearmotor (cable not included).

Magnetic Encoder with Top-Entry Connector on a Mini Plastic Gearmotor (cable not included).

Cable options

We have two types of cables with matching JST SH-style connectors that can be used with these encoders. Single-ended versions have a connector on one end and unterminated wires on the other, while double-ended cables have twisted wires with female connectors on both ends.

Single-ended cables:

• 75 cm (30″) • 30 cm (12″) • 12 cm (4.5″)

Double-ended cables:

• 63 cm (25″) • 40 cm (26″) • 25 cm (10″) • 16 cm (6.3″) • 10 cm (4″)

The double-ended cables can be used with our JST SH-style connector breakout boards (available in top-entry and side-entry versions) to easily access the motor and encoder pins on a standard solderless breadboard. The right picture below shows an example of this with our similar micro metal gearmotor encoder.

6-Pin female JST SH-style connector.

Top-Entry and Side-Entry Breakout Boards for JST SH-Style Connectors, 6-Pin Male.

Side-entry JST SH-style connector breakout board in a breadboard, female-female cable, and encoder with connector mounted on a Micro Metal Gearmotor.

Pinout and installation

The encoder board is designed to be soldered directly to the back of the motor, with the back shaft of the motor protruding through the hole in the middle of the circuit board. One way to achieve good alignment between the board and the motor is to tack down the board to one motor pin and to solder the other pin only when the board is flat and well aligned. Be careful to avoid prolonged heating of the motor pins, which could deform the plastic motor case or the motor brushes. Once the board is soldered down to the two terminals, the motor leads are connected to the M1 and M2 connector pins as labeled below, and they can be accessed via the red and black wires when used with our corresponding JST cables. The remaining four connector pins are used to power the sensors and access the two quadrature outputs:

Pin	Wire color	Function
1	Green	encoder GND
2	White	encoder channel B output
3	Yellow	encoder channel A output
4	Blue	encoder Vcc (2.7 V to 18 V)
5	Black	motor power M2
6	Red	motor power M1

The sensors are powered through the VCC (blue wire) and GND (green wire) pins. VCC can be 2.7 V to 18 V, and the quadrature outputs A and B (yellow and white wires) are digital signals that are either driven low (0 V) by the sensors or pulled to VCC through 10 kΩ pull-up resistors, depending on the applied magnetic field. The sensors’ comparators have built-in hysteresis, which prevents spurious signals in cases where the motor stops near a transition point.

Encoder A and B outputs of a magnetic encoder on a high-power (HP) mini plastic gearmotor running at 4.5 V.

Schematic diagram

Comparison to older versions

This encoder module improves on our previous encoder boards for mini plastic gearmotors by adding a connector to enable the use of removable cables. The basic schematic is unchanged, and the electrical performance is identical aside for the lower minimum operating voltage. The following pictures show the two newer encoders with JST SH-type connectors next to the original ones:

Magnet-side view of the Magnetic Encoder with Top-Entry Connector for Mini Plastic Gearmotor, 12 CPR, 2.7-18V.

Magnet-side view of the Magnetic Encoder with Side-Entry Connector for Mini Plastic Gearmotor, 12 CPR, 2.7-18V.

Romi Encoder Pair Kit, magnet-side view of PCB.

Magnetic Encoder Kit for Mini Plastic Gearmotors, magnet-side view of PCB.