Issue with Incorrect Encoder Values – SparkFun Auto pHAT and Hobby Motor with Encoder

Robotics
1

Dear Customer Service Team,

I am currently using the following products:

  • SparkFun Auto pHAT for Raspberry Pi (ROB-16328)
  • Hobby Motor with Encoder - Metal Gear (ROB-16413)

I am encountering an issue where, when reading the encoder values, I occasionally receive incorrect readings. For example, out of 50 encoder counts, I sometimes get a value like “-120” in the middle of the series, and then the values continue as expected (e.g., “50”).

As this is my first time working with encoders, I am wondering if this behavior is normal, or if I might be doing something wrong.

To mitigate the issue, I have implemented a kind of damping in my code: values that deviate by more than 15% from the previous reading are ignored. However, I am wondering if there are other, more effective approaches to handle this problem.

Has anyone experienced something similar, or can suggest ways to improve the accuracy of the encoder readings?

2

Please post the code, using code tags.

If you are using interrupts, that behavior is a typical result of not following the stringent rules for interrupt coding.

1 Like
3

I am using the code from the SparkFun Auto pHAT Hookup Guide. Here is a screenshot of the described effect.

image
image281×295 22.7 KB

4

Here’s the code from the encoder demo

#!/usr/bin/env python
#-----------------------------------------------------------------------------
# ex1_qwiic_dual_encoder_reader.py
#
# Simple Example demonstrating how to read encoder counts for the Qwiic Dual Encoder Reader (as part of the SparkFun Auto pHAT)
#------------------------------------------------------------------------
#
# Written by  SparkFun Electronics, May 2019
# 
# This python library supports the SparkFun Electroncis qwiic 
# qwiic sensor/board ecosystem on a Raspberry Pi (and compatable) single
# board computers. 
#
# More information on qwiic is at https://www.sparkfun.com/qwiic
#
# Do you like this library? Help support SparkFun. Buy a board!
#
#==================================================================================
# Copyright (c) 2019 SparkFun Electronics
#
# Permission is hereby granted, free of charge, to any person obtaining a copy 
# of this software and associated documentation files (the "Software"), to deal 
# in the Software without restriction, including without limitation the rights 
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 
# copies of the Software, and to permit persons to whom the Software is 
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all 
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 
# SOFTWARE.
#==================================================================================
# Example 1
#

from __future__ import print_function
import qwiic_dual_encoder_reader
import time
import sys

def runExample():

    print("\nSparkFun Qwiic Dual Encoder Reader   Example 1\n")
    myEncoders = qwiic_dual_encoder_reader.QwiicDualEncoderReader()

    if myEncoders.connected == False:
        print("The Qwiic Dual Encoder Reader device isn't connected to the system. Please check your connection", \
            file=sys.stderr)
        return

    myEncoders.begin()

    while True:

        print("Count1: %d, Count2: %s" % (myEncoders.count1, \
            myEncoders.count2, \
            ))

        time.sleep(.3)

if __name__ == '__main__':
    try:
        runExample()
    except (KeyboardInterrupt, SystemExit) as exErr:
        print("\nEnding Example 1")
        sys.exit(0)