DRO Adapter for Glass and Magnetic Scales V2

TouchDRO Adapter for Glass and Magnetic DRO scales includes a fully assembled mainboard, a set of Dsub-9 connector harnesses that can be customized to match the pinout of your particular scales, and [optionally] a lazer-cut DIY cast acrylic enclosure kit. The DRO adapter is optimized for demanding industrial applications. It supports most modern glass and magnetic DRO scales, as well as incremental rotary encoders that output either differential or single-ended quadrature signal.


This is an updated version of the TouchDRO adapter for Glass and Magnetic Scales. It supports up to four scale inputs, tachometer input, touch probe/tool setter input, and up to four axis limit switches. The adapter can handle single-ended (TTL) and differential (RS-422) quadrature signals and supports most modern glass and magnetic DRO scales that output a 5V quadrature signal.

The adapter is sold as a ready-to-use board with a set of scale connector harnesses that can be configured for your specific scale pinout. Each adapter is built from high-quality name-brand components to stringent IPC-A-610 Class II or better standard. I personally inspect, program, and test each and every unit before shipping it to you and ensure excellent performance and long-term reliability.


  • Four scale inputs (differential and single-ended scales)
  • Tachometer input with a wide RPM range
  • Touch probe/tool setter input (TouchDRO app support coming in the next version)
  • Limit switch inputs for each axis
  • Powerful multi-core 32-bit processor for outstanding performance and reliability
  • Bluetooth connectivity for a clutter-free installation

Purchase Options

This TouchDRO adapter can be purchased as a standard kit that includes only the mainboard and a set of standard panel-mounted D-Sub 9 connectors, or as a complete "No Solder" kit that comes with a set of press-fit D-Sub 9 pigtail connector assemblies, a lazer-cut acrylic enclosure kit and all of the necessary hardware. The contents are as follows:

4-axis DRO Kit with Enclosure

  1. TouchDRO Glass scale Adapter mainboard
  2. Press-fit (no soldering required) D-Sub connector kit:
    • Four press-fit panel mounted Dsub-9 female connector housings
    • Four 4x2 Molex connector housings
    • 24 pre-crimped leads (6 leads per axis)
    • 4-axis stainless steel hardware kit
  3. Lazer-cut acrylic enclosure kit (unassembled)
DIY digital readout adapter for Glass and Magnetic DRO Scales

3-axis DRO Kit with Enclosure

  1. TouchDRO Glass scale Adapter mainboard
  2. Press-fit (no soldering required) D-Sub Connector Kit:
    • Three press-fit panel mounted Dsub-9 female connector housings
    • Three 4x2 Molex connector housings
    • 18 pre-crimped leads (6 leads per axis)
    • 3-axis stainless steel hardware kit
  3. Lazer-cut acrylic enclosure kit (unassembled)
DIY digital readout adapter for Glass and Magnetic DRO Scales

2-axis DRO Kit with Enclosure

  1. TouchDRO Glass scale Adapter mainboard
  2. Press-fit (no soldering required) D-Sub Connector Kit:
    • Two press-fit panel mounted Dsub-9 female connector housings
    • Two 4x2 Molex connector housings
    • 12 pre-crimped leads (6 leads per axis)
    • 2-axis stainless steel hardware kit
  3. Lazer-cut acrylic enclosure kit (unassembled)
DIY digital readout adapter for Glass and Magnetic DRO Scales

Board with D-Sub Connectors

Adapter board with D-Sub connectors is a good choice if you are cofortbale with some basic soldering and can provide your own non-metallic enclosure.

  1. TouchDRO Adapter mainboard
  2. Four panel-mounted Dsub-9 female connectors
  3. Set of female-to-female Dupont jumper wires
DIY digital readout adapter for Glass and Magnetic DRO Scales 4-axis kit contents


Supported Scales

This TouchDRO adapter supports a vast majority of Glass and Magnetic DRO scales on the market that output 5-Volt quadrature signal. This includes virtually all Chinese DRO scales from brands like Easson, Ditron, Sino, and many others. The majority of modern scales from well known western DRO brands are supported, as long as they provide 5V quadrature output. This includes most EMS (Electronica Mechatronic Systems) magnetic scales, many Accu-Rite scales, etc.

To determine if your scales are supported, look for the pinout diagram or pin descriptions in the scale's manual or spec sheet.

  • If there are pins labeled +5V, 0V (or Ground), "A" and "B", the scale outputs a single-ended quadrature signal. Additionally, if there are pins marked A' and B' (or alike), the scales output a differential quadrature signal.
  • Scales that have pins labeled "Data", "Clock", "En", etc. are not compatible, as are the scales that require a negative power supply or power supply exceeding 5V.

Supported Rotary Encoders

Any of the scale inputs can be used with incremental 5V rotary encoders with push-pull or "open drain" (also called "open collector" or "NPN") output.


Scale Inputs 4
Angular Axis Yes*
Tachometer Input Yes
Probe/Height Setter Yes
Axis Limit Switches 4
Power Supply 5V DC, Micro-USB
Current Draw Approx. 250 mA
Width 3.1"/78.7mm
Length 2.5"/63.5mm

* Shares input with the fourth linear axis

Recommended Operation Conditions

  Min Typical Max
Axis Input Edges/Second 100,000 (100KHz) 200,000 (250KHz)
Tachometer Pulses/Second 0.5 1,000 10,000
Position refresh rate 1Hz (idle) 25Hz (active)
RPM refresh rate 1Hz 1Hz
Probe/Limit switch trigger time 0.2s 20us 100us

Absolute Maximum Ratings

  Min Typical Max
Supply Voltage* 3.3V 5.0V 5.5V
Current Draw 20mA 120mA 300mA
Scale Signal "High" Level 2V 5.0V 5.8V
Scale Signal "Low" Level 0V 0V 0.8V
Probe/Tach/Home signal "High" Level 3.9V 5V 5.5V
Probe/Tach/Home signal "Low" Level 0V 0V 1.1V
Other inputs (Prog., JTAG, SPI) 0V 3.3V 3.6V

*Lower supply voltage might be higher for some scales. 3.3V is the lowest level at which the main processor will operate.

Mechanical Dimensions

Fig 1: Mechanical Dimensions


Useful Resources

Port Functions

Fig 2: Input Ports
Port Description 5V-Tolerant Note
X,Y,Z,W Inputs for four linear axes Yes Pulled up to 3.3V via weak internal pull-ups
Tach. Tachometer input Yes Pulled up to 5V
Probe Touch probe input Yes Pulled up to 5V
LIM.X-LIM.W Axis limit switch inputs Yes Pulled up to 5V
J6 5V Power input N/A Micro-USB input jack
J5 5V Power input/output N/A Connected in parallel to J6
PROG ESP32 Programming Port No Used to re-program ESP32
J7 Diagnostics switch No Disabled in production firmware
J8 SPI Port No Not used; for future expansion

Axis Input Pin Functions

Inputs for the scales are located along the left edge of the board, with the first axis (X) on the top and last (W) at the bottom. Each scale input uses a 2x4 pin header that has the following connections:

  • Vcc - +5V supply for the scale
  • A - primary input from A channel
  • A' - complementary input from A channel
  • B - primary input from B channel
  • B' - complementary input from B channel
  • Ground - 0V (connected to the chassis ground

Inputs A' and B' are optional. If left unconnected, the readout will still work as expected. If the scales support differential output, it's recommended to connect the differential channels for better noise immunity when using long cable runs (over 5 meters).


The adapter uses a pulse-counter tachometer input that can work with sensors that output a 5V "push/pull" signal or "open drain" (also called "open collector" or "NPN") sensors. The firmware can calculate the RPM with pulse frequency as low as 0.5Hz and as high as 10KHz, but for best accuracy and reliability it's recommended to use encoder disks that produce pulse frequency between 10Hz and 1KHz during normal operation.

Touch Probe/Tool Setter Input

Probe/tool setter support will be available in the TouchDRO application starting with V3.

Probe/Tool Setter input is a 5V-tolerant binary (on/off) input that can be used with either normally-open or normally-closed touch probes and tool height setters. The switch type is detected at boot time.

IMPORTANT:If the probe has an LED, it has to be reverse-biased (backward), or the input won't work. To test this, connect the probe to Vcc and Ground. If the LED lights up (either when the probe is touching, or not touching), reverse the leads.

Axis Home Switch Inputs

Each of the four axis inputs has a corresponding limit switch input that can be used to manually home the machine. When used with repeatable switches, TouchDRO can simulate the functionality of high-end DRO scales that have "origin" marks or "home" areas.

The pins are pulled to 5V using large value resistors and should be used with normally-open switches. When a "limit" pin is pulled to the ground, the readout for the given axis is zeroed out in the firmware.

Assembly and Setup

Identify Scale Connector Pinout

Refer to your scale's documentation to determine the pin functions of the scale's D-Sub connector. Relevant pins are +5V, 0V, A, and B; A' and B' are available only on scales with differential output.

Unbranded Chinese scales often come with the wrong documentation or lack it altogether. Fortunately, most of these scales are based on the same circuit (with minor variations) and the pinout can be relatively easily reverse-engineered using instructions described in "How to Find Glass DRO Scale Pin Functions".

Connect the Scales

To operate correctly each scale needs to have +5V, Ground and at least A and B lines connected. Lines A' and B' (on differential scales) provide better noise immunity but are otherwise optional.

"No Soldering" Kit

The no-solder kit comes with four sets of pre-crimped leads (loose), four 4x2 Molex connector housings, and four D-Sub 9 press-fit connector housings. Assembling the harnesses doesn't require any soldering or special tools, but a set of needle-nose pliers makes inserting the pins into connector housings much easier than using bare fingers. The process is as follows:

  1. Set aside four or six leads (four for single-ended scales, six for differential)
  2. Insert the gold-plated pins into the D-Sub connector housing by gripping the lead right behind the pin. The pins are symmetrical, so there is no particular orientation.
    DIY DRO Adapter for Glass Scales inserting pin into D-Sub connector
    Use needle nose pliers to press-in the pin
  3. Insert the tin-plated pins into the Molex connector housing, referring to the diagram from the "Input Pin Functions". These pins need to be inserted with the tabs facing the same way as the small holes on the housing, as shown below.
    DIY DRO Adapter for Glass Scales inserting pin into Molex housing
    Insert pins into the Molex housing with tabs facing outwards

IMPORTANT:Once the D-Sub connector pins are pressed in, removing them requires a special tool.

There are six lead colors. While there is no standard connection scheme, it's recommended to use Black for "Ground" and Red for "+5V". Green/Blue and White/Yellow can be used for A/A' and B/B' respectively.

Standard Kit

The standard kit comes with panel-mounted female D-Sub 9 connectors and a set of Dupont jumper wires. To assemble the harnesses you will need to cut the jumper wires that you can use to make four sets of leads. The process is as follows:

  1. Separate the ribbon cable into sections with four or six wires (four for single-ended scales, six for differential).
  2. Cut each section in half and trim to the desired length. It's best to leave a bit of slack, so the cables are not under strain while mounted in the enclosure.
  3. Strip and tin the cut ends
  4. Solder the leads to the appropriate pins
  5. Using the diagram from the "Input Pin Functions", connect the female ends of the Dupont leads to the TouchDRO adapter.

Since the TouchDRO adapter will be likely subjected to vibration, it's recommended to hot-glue the connectors to the board to prevent them from coming loose during use.

Mount the Adapter into An Enclosure

TouchDRO adapters require a non-metallic enclosure in order for the Bluetooth signal to reach the tablet. Since the electronics don't produce much heat, there are no special material or size requirements for the enclosure, as long as the board fits it.

A standard 115mm x 90mm x 55mm ABS enclosure with clear top works very well for this adapter and can be purchased for under $10 (USD) from eBay and many other online retailers.

Press-fit the +5V, 0V, A and B, pins into the appropriate position on one of the female D-Sub connectors. To do so, hold the connector firmly in one hand and using a pair of small needle noze pliers, push the gold-plated pin into the hole until you feel a click and a positive stop. Colors should be as follows:

Please note, to ensure the best performance Bluetooth antenna, it's recommended to mount the adapter with at least 5mm gap from the machine frame.


Proper grounding is very important for stable operation of the DRO unit. Although industrial-grade glass and magnetic scales aren't nearly as sensitive to EMF as their capacitive counterparts, electrical noise can still cause problems. The easiest way to reduce EMF issues is to ground the board to the machine's frame. Mounting holes on the board are tied to the ground fill, as are all of the ground pins.