Introduction

This project is a motor speed control sensor that is designed to be used for testing and checking the speed of an electric motor programmed using Arduino. The sensor is used together with a microcontroller to detect speed, limit positions, and count pulses of a given motor. Substantially, a rate meter functions by gauging the frequency of an event. This involves tallying the occurrences within a specified timeframe i.e. integration interval and subsequently dividing the event tally by the elapsed time to determine the rate.

The motor speed sensor module, compatible with microcontrollers, produces pulse trains when its optical sensor is obstructed by a slotted wheel or equivalent. This optical sensor has an LED for illumination and a phototransistor to detect light presence. The setup uses a trans-missive optical sensor with an infrared LED and phototransistor, ensuring protection against ambient light disruption and precise alignment to a specific radiation frequency for enhanced interference resistance.

The Circuit

According to the description, the circuitry can transmit precisely measured pulses to a tachometer based on a microcontroller or an equivalent device. The connection of the hardware is surprisingly straightforward. The core element of the setup is the OS25B10 trans-missive optical sensor, which produces output through a phototransistor (OC1).

Following the venerable LM393 dual comparator chip (IC1), which functions as a basic Schmitt trigger which are circuits with multiple applications such as extracting digital data from highly noisy environments and signal processing, there is the green indicator (LED1) to signify the presence of applied voltage. Additionally, the red indicator (LED2) detects the output of the motor speed sensor module. Operating the module on a voltage range of 4.5V to 5.5V DC is advisable.

Be aware that an R1 resistor with a resistance of 180 ohms is used to control the operating current of the LED in the OC1 sensor, model OS25B10. You might need to modify this resistor’s value during the prototype stage. Also, consider adjusting the resistance of the R2 resistor with a value of 10 kilohms, to get a good voltage swing in your practical application. The R7 resistor having 10 kilohms serves as an alternative pull-up resistor.

The Encoder Disc

The optical sensor includes a LED and a photoresistor on opposite sides. When the path is unblocked, the photoresistor conducts, but when blocked it doesn’t. By placing an encoder disc in the sensor’s slot, we can measure the rotation rate of a connected motor/wheel. The below image shows an encoder disk (index wheel) with multiple slots. Design your own using stainless steel or hard plastic for speed sensing with just one set of slots.

Proof of Concept

Built a basic prototype on a small perf board with some components soldered at the bottom. Connected it to an Arduino board to measure a geared robot motor’s rpm (150rpm@5V) using a homemade encoder disc (12 slots/disk). The results were close to the motor’s specified rpm value. Arduino hardware hookup and demo sketch are provided below. Give it a try!

Alternatively

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