Adapter Board for Shahe and iGaging Capacitive DRO Scales

Monday, February 25, 2019
Capacitive Scale DRO Adapter

TouchDRO adapter for iGaging and Shahe scales is designed to work with several models of 3V capacitive linear DRO scales manufactured by Sanhe Measuring Instrument Co.,Ltd. and distributed under different brand names. It supports up to four linear scales, directional tachometer and a probe or tool height setter input. The circuit is designed and laid to provide reliable operation of capacitive DRO scales and significantly reduce the effect of shop noise and electrical interference on the scales, compared to a do-it-yourself adapter.

Scale Compatibility

The adapter supports the following capacitive digital readout scales:

  • iGaging DigiMag (the original "Remote DRO" scales)
  • AccuRemote Digital Remote Readout
  • Shars "Digital Machine Aluminum Scale" (SKU 303-927x)
  • iGaging EZ-View DRO Plus
  • iGaging Absolute DRO Plus1
  • Shahe 5403-xxx2 Digital Linear Scale with Remote Display ("Round Head" model)
  • Shahe 5404-xxx2 Digital Linear Scale with Remote Square Display

1 Older non-Plus Absolute DRO scales use different protocol and are not supported

2 Shahe 5403 and 5404 scales are supported as of firmware version 2.0

Purchase Options

The TouchDRO adapter for Shahe and iGaging scales can be purchased in two different configurations to suit Mini and Micro USB scale variants. Both use the same base board running the same firmware but differ in the connection options.

With USB Micro-B Connectors

By default the TouchDRO adapter is sold as a plug-and-play board with four pre-installed USB Micro-B female connectors. It is pin-compatible with the newer iGaging DigiMag, iGaging EZ-View DRO and iGaging Absolute DRO Plus scales that use Micro USB cables. The board is fully assembled, programmed and tested. To complete the setup you will need to provide a non-metallic enclosure and a suitable power supply. No further electronic assembly or scale modification is needed.

With USB Mini-B Breakout Boards

For use with older iGaging scales and the new Shahe 5404 scales the board can be purchased as a kit that includes four USB MIni-B breakout boards and a set of jumper wires. The adapter board is fully assembled, programmed and tested, and comes with a set of five-pin headers pre-installed in lieu of the Micro-B connectors. A similar set of headers is pre-installed on the breakout boards. To complete the setup you will need to connect scale output pins to the correct input pins using the provided jumper wires, as well as procure a non-metallic enclosure and a suitable power supply. No soldering is required.

Note on Shahe 5403 (Round Head) Scales

While the board supports Shahe 5403-xxx scales, connecting them to the board requires soldering. This version of the scale comes in two variants: one with the cable hard-wired on both ends, and one with the cable hard-wired into the display unit and a USB Mini-B female plug on the reading head. The latter can be used without soldering (in theory) by using USB Mini-B male to Mini-B male cable, but since the scale utilizes the "Id" pin, you will need a 5-conductor cable, which are non-standard and extremely rare.

In practice the most viable approach is to either hard-wire the cable directly to the Micro USB TouchDRO adapter board, or replace the supplied cable with a Micro USB matching the pinout of the EZ-View scales.

Pin Functions

DRO Adapter for iGaging and Shahe DRO Scales

Mechanical Dimensions

DRO Adapter Mechanical Drawing

Status LEDs

The board has two status LEDs:

Green

Green LED is used by the processor to display the adapter data acquisition status. It can be in two states:

  • Board is in protocol detection mode - fast blinking
  • Board is ready to receive position - once per second blinking

Blue

  • Board not paired - two pulses per second
  • Board paired but disconnected - short pulse every 2 seconds
  • Board connected - two short pulses every 2 seconds

Blue LED is connected directly to the BlueTooth transceiver and indicate BlueTooth connection status.

Assembly and Installation

Scale Connection

Depending on the board configuration, connecting the scales might be as simple as plugging them into the on-board Micro-B connectors, or might require making jumper wire connections between the board and the breakout boards as described above. Table below shows the mapping from scale output pins to TouchDRO input pins.

Scale Connector Vcc (3 V) Ground Clock Data
DigiMag USB Micro-B Vcc Ground D- D+
DigiMag USB Mini-B Vcc Ground D- D+
EZ-View USB Micro-B Vcc Ground D- D+
Shahe 5403
AKA "Round Head"
USB Mini-B
(on the reding head)
D- Vcc D+ Id
Shahe 5404
AKA "Square Head"
USB Mini-B Id D+ D- Vcc
Absolute DRO+ USB Micro-B Vcc Ground and Id D- D+
Absolute DRO+ USB Mini-B Id Ground and Vcc D- D+

Important note: all scales should be plugged in before the board is powered on, since scale protocol detection happens during the first two seconds after power-up. Any scales that are not plugged in when the board boots up will be ignored.

Tachometer Connection

The board is setup to accept a directional tachometer that has either push-pull or line driver quadrature output. For directional input connect Vcc to 3.3V, A and B outputs, and Ground. If B is not connected the tachometer will be non-directional.

Power Supply

TouchDRO board uses a common 2.1mm x 5mm center-positive DC power jack, similar to the one used by the Arduino boards, therefore any power adapter that provides 5-9V and at least 200 mA will work. If possible, I recommend using an old-style linear "wall wart" adapter with a transformer, as opposed to the newer switching ones. Capacitive scale have their frames connected to the ground, which creates a large ground loop between the machine and the TouchDRO board, which can cause problems under some circumstances. An old style transformer power supply provides a way to cut the loop. Should you experience random scale resets or position jumps when running on or off spindle motors or VFD, please refer to the Three Ways to Improve iGaging DRO Scales Reliability post for ways to avoid those problems.

Grounding

Capacitive scales by their nature are more susceptible to noise and interference than glass or magnetic DRO scales. It is, therefore, extremely important to properly ground your DRO setup to avoid random scale resets or position jumps. Ideally there should be no loops in the ground connection, but since all of scales supported by this controller have their frames grounded, the only practical way to eliminate the loops between sales and the board is to use non-conductive mounting hardware or omit the ground connections to the scales and ground the board to the machine frame. In practice this might not be needed unless you have noise equipment or a powerful motor that creates a lot of noise in the mains lines. More critical is the loop between the machine frame and the scale's power supply. That loop should either be eliminated using a mains-isolating power supply (i.e. an old-style heavy wall wart), or if that is not possible, kept as short as possible.

1 comment :

  1. I use two tachs. ONe with the spindle and the other with the lead screw. That way I can calculate the tpi/pitch on the fly

    ReplyDelete