10 min

Measure the speed and rotation of a spinning object with A17501 and STM32F415RG

Dual-output differential speed and direction sensing solution

Speed Sense Click with Fusion for ARM v8

Published Jan 15, 2024

Click board™

Speed Sense Click

Dev Board

Fusion for ARM v8


NECTO Studio



Easily perform rotational position sensing of a ring magnet target in automotive and industrial electric motor applications, often with specific application and safety requirements



Hardware Overview

How does it work?

Speed Sens Click is based on the A17501, a dual output differential speed and direction sensor from Allegro Microsystems. The sensor consists of three Hall elements incorporated in such a way as to create two independent differential channels. The differential signals are used to produce a highly accurate speed output and, if desired, provide information on the direction of rotation. The advanced self-calibration technique with the digital tracking of the signal results in accurate switch points over the air gap, speed, and temperature. The sensor is immune to common external

magnetic disturbance and is ideally suited for asynchronous electric motor applications. When properly back-biased, the sensor is intended for use with ring magnets or ferromagnetic targets. It poses a temperature-compensated amplifier, as well as a full-range ADC. Besides operating on 5V from the mikroBUS™ socket power rail, you can also add an external power supply over the VEXT connector from 4 up to 24V. The selection can be made over the VIN SEL. Speed Sens Click uses general-purpose IOs to interrupt the host MCU when detecting the magnet on a spinning wheel.

The output channel pins are labeled CHA and CHB. There is also an external header with these channels for connecting an external device (relay, LED, and more). This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the VCC SEL jumper. This way, both 3.3V and 5V capable MCUs can use the communication lines properly. Also, this Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used as a reference for further development.

Speed Sense Click hardware overview image

Features overview

Development board

Fusion for ARM v8 is a development board specially designed for the needs of rapid development of embedded applications. It supports a wide range of microcontrollers, such as different ARM® Cortex®-M based MCUs regardless of their number of pins, and a broad set of unique functions, such as the first-ever embedded debugger/programmer over WiFi. The development board is well organized and designed so that the end-user has all the necessary elements, such as switches, buttons, indicators, connectors, and others, in one place. Thanks to innovative manufacturing technology, Fusion for ARM v8 provides a fluid and immersive working experience, allowing access anywhere and under any

circumstances at any time. Each part of the Fusion for ARM v8 development board contains the components necessary for the most efficient operation of the same board. An advanced integrated CODEGRIP programmer/debugger module offers many valuable programming/debugging options, including support for JTAG, SWD, and SWO Trace (Single Wire Output)), and seamless integration with the Mikroe software environment. Besides, it also includes a clean and regulated power supply module for the development board. It can use a wide range of external power sources, including a battery, an external 12V power supply, and a power source via the USB Type-C (USB-C) connector.

Communication options such as USB-UART, USB HOST/DEVICE, CAN (on the MCU card, if supported), and Ethernet is also included. In addition, it also has the well-established mikroBUS™ standard, a standardized socket for the MCU card (SiBRAIN standard), and two display options for the TFT board line of products and character-based LCD. Fusion for ARM v8 is an integral part of the Mikroe ecosystem for rapid development. Natively supported by Mikroe software tools, it covers many aspects of prototyping and development thanks to a considerable number of different Click boards™ (over a thousand boards), the number of which is growing every day.

Fusion for ARM v8 horizontal image

Microcontroller Overview

MCU Card / MCU



8th Generation


ARM Cortex-M4

MCU Memory (KB)


Silicon Vendor


Pin count


RAM (Bytes)


Used MCU Pins

mikroBUS™ mapper

Channel B Output
Power Supply
Channel A Output
Power Supply

Take a closer look


Speed Sense Click Schematic schematic

Step by step

Project assembly

Fusion for PIC v8 front image hardware assembly

Start by selecting your development board and Click board™. Begin with the Fusion for ARM v8 as your development board.

Fusion for PIC v8 front image hardware assembly
Buck 22 Click front image hardware assembly
SiBRAIN for PIC32MZ1024EFK144 front image hardware assembly
v8 SiBRAIN MB 1 - upright/background hardware assembly
Necto image step 2 hardware assembly
Necto image step 3 hardware assembly
Necto image step 4 hardware assembly
NECTO Compiler Selection Step Image hardware assembly
NECTO Output Selection Step Image hardware assembly
Necto image step 6 hardware assembly
Necto image step 7 hardware assembly
Necto image step 8 hardware assembly
Necto image step 9 hardware assembly
Necto image step 10 hardware assembly
Necto PreFlash Image hardware assembly

Track your results in real time

Application Output

After pressing the "FLASH" button on the left-side panel, it is necessary to open the UART terminal to display the achieved results. By clicking on the Tools icon in the right-hand panel, multiple different functions are displayed, among which is the UART Terminal. Click on the offered "UART Terminal" icon.

UART Application Output Step 1

Once the UART terminal is opened, the window takes on a new form. At the top of the tab are two buttons, one for adjusting the parameters of the UART terminal and the other for connecting the UART terminal. The tab's lower part is reserved for displaying the achieved results. Before connecting, the terminal has a Disconnected status, indicating that the terminal is not yet active. Before connecting, it is necessary to check the set parameters of the UART terminal. Click on the "OPTIONS" button.

UART Application Output Step 2

In the newly opened UART Terminal Options field, we check if the terminal settings are correct, such as the set port and the Baud rate of UART communication. If the data is not displayed properly, it is possible that the Baud rate value is not set correctly and needs to be adjusted to 115200. If all the parameters are set correctly, click on "CONFIGURE".

UART Application Output Step 3

The next step is to click on the "CONNECT" button, after which the terminal status changes from Disconnected to Connected in green, and the data is displayed in the Received data field.

UART Application Output Step 4

Software Support

Library Description

This library contains API for Speed Sense Click driver.

Key functions:

  • speedsense_get_speed - This function reads the state of the CHA pin used for speed output protocols

  • speedsense_get_direction - This function reads the state of the CHB pin used for direction output protocols

Open Source

Code example

This example can be found in NECTO Studio. Feel free to download the code, or you can copy the code below.

 * @file main.c
 * @brief Speed Sense Click Example.
 * # Description
 * This library contains the API for the Speed Sense Click driver 
 * for the speed and direction signal state detection for every magnetic pole pair.
 * The demo application is composed of two sections :
 * ## Application Init
 * Initialization of GPIO and log UART.
 * ## Application Task
 * This example demonstrates the use of the Speed Sense Click board. 
 * The demo application displays the direction of movement and rotation speed (rotations per minute) 
 * of the ring magnet with three pairs of rotating poles positioned in the sensor operating range.
 * @author Nenad Filipovic

#include "board.h"
#include "log.h"
#include "speedsense.h"


uint8_t start_measure = SPEEDSENSE_STOP_MEASURE;
uint32_t time_cnt = 0;
uint32_t signal_duration = 0;
uint32_t start_timer = 0;

static speedsense_t speedsense;   /**< Speed Sense Click driver object. */
static log_t logger;    /**< Logger object. */

void application_init ( void ) 
    log_cfg_t log_cfg;  /**< Logger config object. */
    speedsense_cfg_t speedsense_cfg;  /**< Click config object. */

     * Logger initialization.
     * Default baud rate: 115200
     * Default log level: LOG_LEVEL_DEBUG
     * @note If USB_UART_RX and USB_UART_TX 
     * are defined as HAL_PIN_NC, you will 
     * need to define them manually for log to work. 
     * See @b LOG_MAP_USB_UART macro definition for detailed explanation.
    LOG_MAP_USB_UART( log_cfg );
    log_init( &logger, &log_cfg );
    log_info( &logger, " Application Init " );

    // Click initialization.
    speedsense_cfg_setup( &speedsense_cfg );
    SPEEDSENSE_MAP_MIKROBUS( speedsense_cfg, MIKROBUS_1 );
    if ( DIGITAL_OUT_UNSUPPORTED_PIN == speedsense_init( &speedsense, &speedsense_cfg ) ) 
        log_error( &logger, " Communication init." );
        for ( ; ; );

    log_info( &logger, " Application Task " );
    log_printf( &logger, "-----------------------\r\n" );

void application_task ( void ) 
    uint8_t direction = 0, speed = 0;
    speed = speedsense_get_speed( &speedsense );
    direction = speedsense_get_direction( &speedsense );

    if ( start_measure & speed )
        signal_duration = time_cnt - start_timer;
        start_timer = time_cnt;
        if ( SPEEDSENSE_DIR_STATE_FWD == direction )
            log_printf( &logger, " Direction: Forward\r\n" );
            log_printf( &logger, " Direction: Reverse\r\n" );
        log_printf( &logger, " Speed: %.2f [rpm]\r\n", SPEEDSENSE_CALC_RMP / signal_duration );
        log_printf( &logger, " Duration: %lu [ms]\r\n", signal_duration );
        log_printf( &logger, " Time: %lu  [ms]\r\n", time_cnt );
        log_printf( &logger, "-----------------------\r\n" );
        start_measure = SPEEDSENSE_STOP_MEASURE;
    else if ( ( !start_measure ) & ( !speed ) )
        start_measure = SPEEDSENSE_START_NEW_MEASURE;

    Delay_ms( 1 );

void main ( void ) 
    application_init( );

    for ( ; ; ) 
        application_task( );

// ------------------------------------------------------------------------ END

Additional Support