Adapter for Glass Scales V2 has been replaced by the new TDA-400/420 Adapter Series.
The new adapter will be available in the first week of February. You will be able to pre-order a unit in a few days.

DRO Adapter for Glass and Magnetic Scales V2

TouchDRO Adapter for Glass and Magnetic DRO scales 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. The adapter can be purchased pre-cofigured for common DRO scales, or as an unassembled kit. Scroll down for more information.


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.

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 to 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

4-axis DRO Kit with 3D Printed Enclosure

The "No Solder" kit 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:

  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. 3D-Printed Enclosure (unassembled)
DIY digital readout adapter for Glass and Magnetic DRO Scales No Soldering kit contents

Fully Asembled TouchDRO Adapter

Fully assembled adapter comes pre-configured for scales from some popular manufacturers and is ready for use.
You will need to provide a compatible Micro-USB power supply, such as an phone charger.

Fully assembled DRO adapter for Optical and Magnetic DRO Scales

Please refer to the "Recommended Scales" page for recommended DRO scales and suppliers.

Before placing an order, please confirm the pinout of your scales in the documentation provided by the supplier.
Current pinout options are as follows:

Option A - Electronica/EMS

This configuration is for Electronica/EMS scales sold by DRO Pros in the USA. If you are planning to purchase your scales from a different supplier, please confirm that the scales use the same pinout.

Pin 1 2 3 4 5 6 7 8 9
RS-422 w/Reference +Z -Z Vcc/5V Shield OV/Gnd +A -A -B +B
Option B - Ditron/Sino/Aikron

Scales from Ditron, Sino and Aikron use identical pinout. Depending on the scale model, some pins might be left disconnected.

Pin 1 2 3 4 5 6 7 8 9
RS-422 w/Reference A'/A- 0V B'/B- Shield/Ground R'/Z' A +5V B R/Z
RS-422 w/o Reference A'/A- 0V B'/B- Shield/Ground   A +5V B  
TTL w/Reference   0V   Shield/Ground   A +5V B R/Z
TTL w/o Reference   0V   Shield/Ground   A +5V B  
Option C - Generic Chinese Scales

This is one of the common DB9 pin configurations used by various Chinese DRO scale resellers. In the USA, this includes Vevor and some other resellers on Amazon and eBay.

Pin 1 2 3 4 5 6 7 8 9
TTL w/Reference   0V       A 5V B R1/Z
Option D - Generic Chinese Scales

This is another common DB9 pin configurations used by various Chinese DRO scale resellers.

Pin 1 2 3 4 5 6 7 8 9
TTL w/ Reference +5 0V A B R/Z/Abs        
TTL w/o Reference +5 0V A B          
Custom Pinout

If your scales are not covered by one of the above configurations, but you prefer to order a fully assembled adapter, we can configure it for you.

Please note: you will need to contact us after placing the order and provide the documentation for your scales that shows the connector pin assignment.


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.

For the up-to-date list of recommended scales and vendors see Recommended DRO Scales

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


  • Scales that have pins labeled +5V, 0V (or Ground), "A" and "B" output "single-ended" quadrature signal.
  • Scales that have are pins marked A' and B' (or alike) output "differential" signal.

Not Supported

  • Scales that have pins labeled +1V, V1+/V1-, or V2+/V2- (or similar) output sine wave and need a priprietary interpolation circuit
  • Scales that have pins labeled -5V, -7V or -24V require negative power supply and are not supported directly
  • Scales that have pins labeled "Data", "Clock", "En", etc. are not compatible

Rotary Encoders

The adapter directly supports 5V incremental rotary encoders with push-pull or "open drain" (also called "open collector" or "NPN") output. Encoders with PNP, or "open sink" otput are not supported.


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) 250,000 (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

*Min. supply voltage requirement 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

Detailed assembly instructions for the Deluxe Kit can be found on the Glass/Magnetic Scale Adapter Quick Start page.

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.

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.