This is the Wheel Encoder Kit from DAGU, a simple add-on to any wheeled robot that can help measure the speed or distance the chassis travels.
Each wheel encoder kit consists of two neodymium 8-pole magnets with rubber hubs and two hall-effect sensors terminated with 150mm cables and 3-pin female servo headers.
These wheel encoders require a supply voltage of 3-24V with a supply current of 4mA.
 

Features:

• Supply Voltage: 3-24V
• Supply Current: 4mA per sensor
• Output Voltage: 26V Max
• Output Current: 25mA Continuous

Documents:

• Datasheet