Arduino Spindle Encoder : Angle/RPM display

This is the design and files for a lathe spindle encoder.

Available functionalities :

• use the lathe's spindle as a dividing head for various circular patterns

  • accurate angular positionning with a 0.1 degrees step
  • setting zero by long button press (in angular mode only)
  • optional : absolute encoder mode (requires Z pin on encoder and activating a #define)

• monitor real spindle speed

  • real time display in rotation par minute display (RPM)
  • useful in case of a VFD or DC motor or to monitor motor load during work
  • works in forward and reverse

• optional : raw encoder value display

• optional : interrupt service routine timing

  • if enabled, used LED BUILTIN pin by default, configurable
  • currently, on an Arduino UNO, ISR duration is 20 usec (50000x per second)

Prototypes

Pinout

Pin type	Pin use	Arduino UNO	Atmega / DIP28
Output	LED A SRC	D9	PB1 / pin 15
Output	LED B SRC	D13	PB5 / pin 19
Output	LED C SRC	D5	PD5 / pin 11
Output	LED D SRC	D7	PD7 / pin 13
Output	LED E SRC	D8	PB0 / pin 14
Output	LED F SRC	D10	PB2 / pin 16
Output	LED G SRC	A0	PC0 / pin 23
Output	LED DP SRC	D6	PD6 / pin 12
Output	LED D1 SINK	A2	PC2 / pin 25
Output	LED D2 SINK	A3	PC3 / pin 26
Output	LED D3 SINK	A4	PC4 / pin 27
Output	LED D4 SINK	A5	PC5 / pin 28
Output	DEBUG/TIMING	D11	PB3 / pin 17
Input	ENCODER A	D2	PD2 / pin 4
Input	ENCODER B	D3	PD3 / pin 5
Input	ENCODER Z	D4	PD4 / pin 6
Input	BUTTON	D12	PB4 / pin 18

Arduino UNO breadboard prototype

Uses on-board 16 MHz crystal

Atmega8A (or Atmega328p, or similar...) perfboard

IMPORTANT : Uses on-chip internal 8 MHz oscillator, no on-board crystal.

Schematic

Perboard-compatible PCB layout

EasyEDA preview

Top copper layer and through holes

Bottom copper layer and through holes :

If you chose to order PCBs from any manufacturer, just keep the display as last thing to solder

Perfboard soldering

General hints

• Start by placing the microcontroller socket, with "pin 1 marker" on column C and row 8
• Only solder the microcontroller non-connected pins : 9, 10, 21, and 24
• Then build/prepare all the other links, except those who connect to the display :
  • Most of the links are done using the legs of the through-hole components
  • Other links are done reusing old (saved) through-hole component legs
  • In these case, the legs were shaped to fit and pre-tacked on one side
  • A couple were made using solid core AWG 34 (0.2 mm2) wire-wrapping + solder
  • But it could have been done like all the remaining AWG 20 (0.5mm2) solid core
  • The most difficult solder joints are the last ones for the display over the socket
  • Where traces overlapped, i either used insulated wire or small heat-shrink over pre-pinned wire

Here is the soldering order i followed, from (1) to (74) :

Special advice for soldering the display :

• Print the horizontal-flip of the PCB (plated holes side), to use as a soldering work sheet
• The perfboard i use is single sided, without plated holes, so no continuity anywhere
• The display is placed above the previous soldered joints, so no access afterwards
• For most, i prepared short straight "old-led-legs wires", soldered from socket pins outwards
• For a few, i pre-looped and soldered solid-core 20 AWG jumper to the top of the display legs
• Finally, i loop/soldered a jumper from pin 23 (mark 51) and looped/soldered it to mark 59
• I placed the display and check that prepared "legs" were bent enough to actually touch display pins
• I checked all display pins again 3 times, because once started, there was no coming back !
• I placed "in the air" and level, with pins barely going past the top side (for later testing)
• I finally soldered marks 64-70, in a "hail mary" style, then finished the floating jumper cables

Verification :

• Print another PCB imagecopy, but this time on the top side to verify connections
• Test all connections for continuity : all should be less than 1 ohm
• Once the capacitor is soldered between VCC and GND, you have increasing Mohm resistance between them

Soldering duration

• it took me 4-6 hours to plan and do it all because i like to take my time
• start some peaceful music and enjoy the process, so you can work steadily
• after a point, there is no second chance, better do it right the first time
• prepare every joint and leg the best it could be, that is good practice
• any training on "unimportant" stuff, ensures a safer ride when "it gets difficult" later.

Here are some picture of the final result :

And i you do not feel like doing it, are not in a rush, or want to get pretty things, order a PCB !

How to connect the board

If you chose to order PCBs from any manufacturer

• the labels will be printed on the silkscreen

If you soldered a perfboard yourself (one with letters on the long side):

• print, cut and laminate the connection card (LibreOffice document)

• screwn terminals

  • letter W : power supply = 5V DC
  • letter U : power supply = GND
  • letter S : button : single pole single throw (SPST) normally-open (NO)
  • letter Q : button : same as above, other leg
  • letter O : quadrature encoder : ground (forwarded on-board from U)
  • letter M : quadrature encoder : power (5V DC forwarded on-board from W)
  • letter K : quadrature encoder : output Z (once per turn)
  • letter I : quadrature encoder : output B (N per turn, phased from A)
  • letter G : quadrature encoder : output A (N per turn)
  • letter E : quadrature encoder : cable shield

• J2 connector : male pin headers for encoder shield grounding

  • letter C/B : optional jumper J2

• J1 connector : male pin headers for UART ICP (conn)

  • row 08 : microcontroller RESET pin (see Requirements for notes about capacitor)
  • row 07 : microcontroller RX pin
  • row 06 : microcontroller TX pin
  • row 05 : microcontroller 5V DC VCC
  • row 04 : microcontroller GND

• H1 connector : female pin headers for timing/debugging

  • pin on column U : signal
  • pin on other column : ground

Limitations

• display is limited to 4 digits

  • max 9999 RPM then overflow
  • do not use encoders with more than 2000 pulses per revolution
  • 1-digit precision (and display) for angular degrees of rotation

• encoder output bandwitch

  • maximum output frequency is 100kHz for the reference below
  • you choice of PPR must satisfy RPM * 4 * PPR / 60 < 100_000
  • because 1 rotation = 4 * number of pulse per revolution = events
  • to chose your encoder PPR, check desired_RPM * PPR < 1 500 000

Error codes

• E003, E006, E009, E012, or any error cumulated error from 1 to 15
  • Cause : this meands a quadrature encoder error because steps were missed
  • Problem : rotation speed was too high, in DEGREE or RAW mode
  • Solutions
    • clear the error by pressing the button (returns to RPM mode)
    • remember to switch to RPM mode before starting spindle motor !

Components

For this project, you will need :

• 1x 5V DC Omron E6B2-CWZ6C rotary encoder with open-collector output
  • https://www.ia.omron.com/product/item/2453/
  • https://www.ia.omron.com/data_pdf/cat/e6b2-c_ds_e_6_3_csm491.pdf
• MCU
  • for prototyping 1x Arduino UNO or any other 5V MCU with enough pins (see requirements below)
  • for pcb/perfboard 1x Atmega8A-like MCU and a 28-DIP socket to solder
• 1x 5641AS Common-Cathode 4-digit 7-segment display
  • https://www.xlitx.com/datasheet/5641AS.pdf

And see Bill of materials for others components :

• resistors
• capacitors
• headers
• terminals

Requirements

• Memory

  • without any features : ~3700 bytes required
  • with USE_Z_RESET : ~80 more bytes required
  • so up to here, a 4K flash MCU without bootloader or with a 256-bytes bootloader would work
  • for all features : ~5900 bytes required, so that usually means an 8K flash

• Electrical characteristics

  • 5V power supply (adapt the display resistors in case of a 3.3V MCU)
  • Consumes 26 milli-amperes when the Arduino UNO rev3 is powered from Vin @5V

• Pins

  • 12 digital output pins to directly drive the display (8 segments + 4 digits)
  • 1 digital input for the push button
  • and for the encoder :
    • either 3 digital input pins (for the referenced encoder)
    • or 2 if your encoder lacks the "Z/home" pin

• Sketch information :

  • Does not need internal pullups
  • Sketch uses 2700 bytes (8% of the UNO's program space)
  • Global variables use 85 bytes (4% of UNO's memory space)

• UART serial programming via ICP headers :

  • a UART-able bootloader present on chip
  • a 5V USB-to-serial to upload new sketches
  • an ceramic (non polarized) 0.1uF capacitor
    • placed in between / in series from DTR/RTS to RESET
    • is not included in the schematic and must be added outside if desired
    • this capacitor is not required if you can time your reset (i can't, lol)
    • what this capacitor actually does ?
      • transforms the falling edge of DTR/RTS to ground,
      • into to a pulse to ground viewed from RESET,
      • allowing RESET to raise again to VCC via the pullup on RESET
      • effectively rebooting the MCU when DTR/RTS changes state

Installation

• Clone the project and open in arduino IDE

• REQUIRED : install digitalWriteFast library

• Option 1 : Using an UNO-as-ISP and breadboard schematic

  • use Sketch / Upload using programmer

• Option 2 : install Minicore or better bootloader and fuse management, and upload over serial

  • Follow https://github.com/MCUdude/MiniCore?tab=readme-ov-file#how-to-install
  • Prepare/Configure your board
    • Set Tool / Board / Minicore / Atmega8A (for example)
    • Set Tool / BOD (Brown out detector) to 4.0V
    • Set Tool / Clock / Internal 16MHz
    • Set Tool / Bootloader / Yes (UART 0)
  • Using an UNO-as-ISP and breadboard schematic
    • use Tool / Burn bootloader (and fuses)
  • Using an USB-to-serial adapter, a breadboard montage, and an non-polarized RESET cap
    • use Sketch / Upload