Amazon 9.8" Pottery Wheel Foot Speed Control Change

Introduction 
This short blog shows how to replace the speed control device in the foot controller on the Amazon 9.8” pottery wheel. This change may be required for anyone with irregular speed control or a damaged foot speed controller.

Determining the Part Replacement
With the pottery wheel unpowered, the internals of the foot speed controller are accessed by removing three plastic screws located in the base of the foot controller. The foot control mechanism consists of a potentiometer for setting the speed and two gears.

Internals of Foot Speed Controller

 To remove the potentiometer, the locking nut was loosened. This allowed removal and part identification.

Original Potentiometer

As shown in the above image, the potentiometer was rated at 4.7 k 2 W. A similar device was located from TE Connectivity part 3-1625931-0 and sourced online.

Replacement TE Connectivity Potentiometer

Items to Address with the Replacement Part
The TE Connectivity potentiometer is a direct replacement for its value (resistance); however, there are mechanical differences with the potentiometer, specifically the solder pins and smooth shaft. Since the original potentiometer was supplied with a D-shaped shaft, the original spur gear could not be reused, so a new spur gear needed to be created.

Original D-Shaft Spur Gear

Down the Spur Gear Road
The spur gear script feature in Fusion 360 was chosen to create a compatible gear. Alternative tools are available for creating a spur gear however these alternatives were not tested for this blog. Two alternative sites may be STL Gears and Gear Generator.

Fusion 360 Spur Gear Script
In Fusion 360, the Spur Gear script is accessed from the Utilities tab under the Add-Ins icon.

SpurGear Script in Fusion360

The settings in the image below were chosen after measuring the original gear, applying them to the spur gear script followed by 3D-printed prototypes. Some important items for the spur gear were the number of teeth, shaft diameter and Fusion 360 calculated Pitch Diameter.

SpurGear Settings in Fusion 360

Fusion 360 Spur Gear Modification
To ensure that the spur gear would not rotate on the round potentiometer shaft, two cutouts were added inside the spur gear shaft area for glue. The cutout changes were made to the spur gear sketch generated by the Fusion 360 script.

Editing the SpurGear Sketch

The images below show the edit to the sketch and updated 3D model.

SpurGear Sketch with Cutouts Added

SpurGear 3D with Cutouts Added

Ultimaker Cura was used to generate a print with a 100 % fill. The Fusion 360 file and STL files are available for downloaded at the end of this blog.

Replacing the Potentiometer
The wiring layout for the potentiometer was recorded. Using a soldering iron, the three wires from the original potentiometer were desoldered.

Potentiometer Wiring Connections

For the replacement potentiometer, the centre pin of the new potentiometer was determined to be the wiper (red wire). In the configuration shown in the image below, pressing the control pedal to the angled position increased the speed. For reverse operation, the yellow and green wire positions on the potentiometer should be swapped. All connections were soldered and covered with a piece of heatshrink.

Wiring for New Potentiometer

The replacement spur gear was printed in PLA and then it was placed onto the potentiometer shaft without glue to ensure it aligned with the other mechanism inside the pedal.

Positioning the Spur Gear

To ensure the gear did not rotate on the potentiometer shaft, glue was added.

Replacement Potentiometer with Round Shaft

Fitting and Setting the Potentiometer Home Position
With the connections finalised and the gear positioned, the locking nut on the potentiometer was hand-tightened.

Mounted Potentiometer with Threadlocker

The pottery wheel was powered and set up to operate from the foot control. In the horizontal position, the potentiometer was rotated so that the pottery wheel did not turn. This corresponds to a speed of 000 on the pottery wheel display. The potentiometer was tightened further. Pressing the foot control to the angled position resulted in a speed of 320.

Maximum Speed Value on Pottery Wheel

Loctite 222 was applied to the thread on the potentiometer to reduce the chance of the potentiometer coming loose.

Lastly, the base plate for the foot control was reattached and secured with the three plastic screws.

Downloads

SpurGear.f3d

SpurGear.stl

Dual Colour LED Matrix Shield (Educational)

Introduction 
This blog shows the hardware used for an Arduino-compatible shield featuring a dual-colour matrix LED.

LED Matrix Shield Mounted on Arduino Uno

Purpose of the LED Matrix
The design was created for educational purposes and to train school-aged programmers. For hobbyists looking for an off-the-shelf solution using LEDs, some related products featuring RGB LEDs are the NeoPixel or for an LED matrix, the D1 Mini from Wemos.

Technology Used
Three shift registers, part 74HC595, were used to drive the 8 rows and 10 columns (matrix 5 red and 5 green LEDs) of the LED matrix from the Arduino Uno. To maintain the design simplicity, no LED buffers were included which would increase the drive current. The 74HC595 from Nexperia fitted to the prototype could provide 25 mA per pin although the maximum current of the shift register is limited to approximately 70 mA.

A buck converter, TI part LMR51606YDBVR was chosen to provide 5V power to the shift register and LED matrix. A higher current DC-DC converter and LED drivers could be utilised for a brighter LED matrix.

Kingbright Dual Colour LED Matrix

For the LED matrix, Kingbright part TBC24-11EGWA was used. At the time of writing the LED Matrix from Kingbright part had become End of Life.

Connections to Arduino
Details are provided on the Arduino website for connecting shift registers such as the 74HC595 to the Uno board. One such example with connections and code is shown in the tutorials.

The shift register connections to the Arduino are the same as the tutorial with the addition of the output enable signal.

To adjust the LED matrix intensity and depending on the characteristics of LEDs, the value of the resistor packs could be changed. During testing the values 68 R and 56 R for red and green LEDs respectively achieved a good balance between current consumption and light output.

LED Matrix Shift Register Connections

Shown in the image below are the pins used on the Arduino Uno for the shift registers and power.

LED Matrix Shift Register to Arduino Connections

 

Lastly, a DC-DC converter was used instead of the linear regulator on the Arduino Uno. This meant less heat dissipation on the Uno board.

LED Matrix Power Supply

Printed Circuit Board (PCB)
The PCB for the LED matrix shield was designed with four layers however the board layer count could be reduced. Shown below are the external power and internal signal layers. The top layer was a solid copper pour for the 0 V layer and therefore not shown.

LED Matrix Bottom Layer PCB

LED Matrix Mid Layer PCB

LED Matrix Mid Layer PCB

Populated LED Matrix
The completed prototype board used pin headers for the LED matrix although the PCB was designed to allow flush mounting of the LED matrix.

Populated LED Matrix Shift Register Side

Populated LED Matrix (Display) Side

When connecting the LED matrix shield to an Uno or similar board, a space between the two boards of at least 13 mm was required. This spacing ensured the LED matrix pins did not cause a short against the USB B connector housing.

Arduino Uno and LED Matrix Fitted Together

LED Matrix Operation & Code
For the example below the Arduino pin mapping shown below was used.

void setup() 
{
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
  pinMode(oePin, OUTPUT);
  digitalWrite(oePin, LOW);
}

Some videos of the operation with example code are shown below.

Counting with Rows

  for (int numberToRows = 0; numberToRows < 255; numberToRows++) 
  {
    digitalWrite(latchPin, LOW);
    shiftOut(dataPin, clockPin, MSBFIRST, 0);           // red = 0, all off 31 show green
    shiftOut(dataPin, clockPin, MSBFIRST, 0);           // green = 0, all off 31 show red
    shiftOut(dataPin, clockPin, MSBFIRST, numberToRows);   // turn on all columns
    digitalWrite(latchPin, HIGH);
    delay(100);
  }

Counting with Columns

for (int numberToColumns = 0; numberToColumns < 32; numberToColumns++) 
  {
    digitalWrite(latchPin, LOW);                                 
    shiftOut(dataPin, clockPin, MSBFIRST, numberToColumns);   // red = 0, all off 31 show green
    shiftOut(dataPin, clockPin, MSBFIRST, numberToColumns);   // green = 0, all off 31 show red
    shiftOut(dataPin, clockPin, MSBFIRST, 255);                        // turn on all rows               
    digitalWrite(latchPin, HIGH);    
    delay(100);
  }

Dual Colour Change

 

  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, MSBFIRST, 0);   // red = 0, all off 31 show green
  shiftOut(dataPin, clockPin, MSBFIRST, 31); // green = 0, all off 31 show red
  shiftOut(dataPin, clockPin, MSBFIRST, 255); // turn on all rows
  digitalWrite(latchPin, HIGH);
  delay(200);
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, MSBFIRST, 31);    // red = 0, all off 31 show green
  shiftOut(dataPin, clockPin, MSBFIRST, 0);     // green = 0, all off 31 show red
  shiftOut(dataPin, clockPin, MSBFIRST, 255); // turn on all rows
  digitalWrite(latchPin, HIGH);
  delay(200); 

Downloads

LED Matrix Gerber

 

LED Matrix Schematic

LED Matrix Top Overlay

LED Matrix Bottom Overlay

Making Amazon 9.8" Pottery Wheel Foot Switch Detachable

Introduction 
In this blog, a modification was made to the generic 9.8” pottery wheel supplied by Amazon. A connector was fitted to allow the foot pedal to be removed.

Amazon Pottery Wheel (Courtesy Amazon)

Pottery Wheel Foot Switch Cable Location
Protruding from the underside of the pottery wheel is a white cable that connects the foot pedal to the pottery wheel’s electronic controls. The connection of the white cable was altered to fit a connector allowing disconnection for movement or storage of the pottery wheel.

Underside View of 9.8" Pottery Wheel

The white cable passes through a hole in the pottery wheel's metal chassis. The hole's internal diameter is approximately 14.8 mm. Depending on the type of chassis mount connector selected, the hole may already be suitable for that connector. Alternatively, an inline pluggable connector could be fitted instead of the chassis mount connector.

An M12 chassis mount and an inline connector set from TE Connectivity was chosen for this project.

Pluggable Connectors
Fitting the M12 chassis mount socket connector started with cutting the white cable. Sufficient cable length was left protruding through the hole to allow for connecting to the chassis mount connector. The cable was moved to the side temporarily while the hole was made larger with a stepped drill bit.

The three wires in the foot pedal cable, red, yellow and green were stripped and tinned. A small length of heatshrink was fitted on each wire. The cable was passed through the retaining nut and then the hole in the chassis. The wires protruding through the hole were soldered to the M12 socket.

Pottery Wheel Side - M12 Chassis Mount Socket

For the mating side of the connector, an M12 plug was fitted to the cable attached to the foot pedal.

Foot Switch Side - M12 Inline Plug

The M12 TE Plug used screw terminals instead of solderable pins. The stripped wires were connected in the same order as the socket.

An operational test was performed before finalising the heatshrink and tightening the M12 nut.

Pottery Wheel M12 Connector Test Fit

The assembled foot switch is pictured below.

Updated Foot Switch Assembly

The connected assembly of M12 connectors is shown below.

Completed M12 Connector Assembly

 

MAX22191 with Periodic Signals

Introduction 
This blog provides measurement information on the maximum input frequency of the Analog Devices digital input device MAX22191. Measurements were taken for the periodic signal types square, sine and sawtooth.

Functional Block Diagram of MAX22191 (Courtesy Analog Devices)

Device Behaviour with Steady State Signals

A small test board was designed for testing the MAX22191.

Circuit for MAX22191 Test Board

The circuit for the MAX22191 followed the datasheet example, consisting of a protection diode (TVS) on the input and an LED on the output. The test board was configured so that the MAX22191 was powered from an external supply.

MAX22191 Development Board

With the MAX22191 powered, the input voltage to the MAX22191 was adjusted to verify the board functionality. The supply (DC 5 V) and input voltages for MAX22191 were controlled using two supplies on a Rigol DP832 power supply.

MAX22191 Setup for Input Voltage Level Tests

Measurements with the test board showed that the upper input threshold voltage (ON) was approximately DC 9.5 V and the lower threshold voltage (OFF) was DC 7.9 V, giving a hysteresis of DC 1.6 V. These values are similar to the device datasheet values for the maximum input upper threshold voltage (ON) of DC 10 V and the lower threshold voltage (OFF) of DC 7 V.

Device Behaviour with Periodic Signals
The output of a function generator Rigol DG1022 was connected to the input of the MAX22191 to test the maximum operating frequency. For the periodic signals, the duty cycle was set and then the frequency of the function generator varied. This process was repeated for three duty cycles. The test board was powered with DC 5 V.

MAX22191 Setup for Periodic Signal Tests

The function generator output was set to High Impedance (High Z). An oscilloscope was connected to the input and output of the test board to capture the waveforms. The images in this section show the input waveform as the yellow trace and the output waveform as the blue trace.

Tests - Square
A square wave with a 10 V amplitude (loaded) was driven into the device.

MAX22191 Output Capture for Square Input Signal

For the three duty cycle settings the frequency of the function generator was increased until the output LED controlled by the MAX22191 switched OFF. The maximum frequency was measured when the output voltage from the MAX22191 dropped below 2.0 V. This was an arbitrary TTL limit for comparative purposes only.

For a 20 % duty, the LED switched OFF at 34 kHz however the output signal fell below the threshold at approximately 30 kHz.

MAX22191 Output Capture for Square Input Signal 20 % Duty

For a 50 % duty, the LED switched OFF at 180 kHz and the output signal fell below the threshold at the same frequency.

For an 80 % duty, the LED switched OFF at 260 kHz and output signals fell below the threshold at approximately 230 kHz. Some unexpected waveform behaviour was seen. This did not occur at lower frequencies such as 150 kHz. This could be an artefact of the test setup.

MAX22191 Output Capture for Square Input Signal 80 % Duty

 

Test - Sine
The LED switched OFF at 123 kHz and the output signal fell below the threshold at approximately 125 kHz.

MAX22191 Output Capture for Sine Input Signal 50 % Duty

 

Tests – Sawtooth
For a 20 % symmetry setting, the LED switched OFF at 34 kHz and the output signal fell below the threshold at the same frequency.

MAX22191 Output Capture for Sawtooth Input Signal 20 % Duty

For a 50 % symmetry, the LED was still active at 120 kHz (function generator limit) and the output waveform was still measurable.

For an 80 % symmetry, the LED was still active at 150 kHz (function generator limit) and the output waveform was still measurable.

MAX22191 Output Capture for Sawtooth Input Signal 80 % Duty

Detection Levels
The periodic signals were captured as shown in the images below to aid in visualising the voltage detection thresholds for the MAX22191.

MAX22191 Input Output Levels Compared to Output for Square Input Signal

MAX22191 Input Output Levels Compared to Output for Sine Input Signal

MAX22191 Input Output Levels Compared to Output for Sawtooth Input Signal