DIY DRO Adapter Kit for Glass Scales

TouchDRO DIY DRO Adapter Kit for Glass Scales (Unassembled) supports up to four 5V quadrature scale inputs, tachometer input, and touch probe/tool setter input. It includes a bare printed circuit board, a microcontroller pre-programmed with TouchDRO firmware, and all of the components needed for building a TouchDRO adapter.

The DIY Digital Readout Adapter Kit for Glass/Magnetic Scales is designed from the ground up to be cost-effective, easy to build and offers excellent performance and reliability. It supports the vast majority of modern Glass and Magnetic DRO scales, as well as standard rotary encoders that output a single-ended 5V quadrature signal. During the assembly, the inputs can be configured to work with PNP, NPN, and Push/Pull encoders for added flexibility.

The adapter uses a fast digital buffer to provide 5 Volt-tolerant input for standard single-ended Glass and Magnetic DRO scales and other quadrature encoders. In conjunction with the optimized TouchDRO quadrature firmware, it can handle a 5-micron movement speed of at least 100mm/second (4 inches/second) when a single axis is in motion or at least 50mm/second when all four axes are moving at once.

This DIY adapter can be used with Glass and Magnetic DRO scales that output a differential signal by omitting the complementary line connections, but for those scales, the pre-made TouchDRO Adapter for Glass and Magnetic scales is recommended.

Kit Contents

This kit comes with high-quality name brand components that are derated to provide ample headroom for long-term reliability and durability. This includes:

Printed circuit board (HASL finish), electrically tested and inspected to meet IPC-A-600 Class II standard
TI MSP430 microcontroller, preprogrammed with TouchDRO firmware
Tested HC-05 BlueTooth transceiver
Set of Texas Instruments ICs (74xx244 buffer and two LM1117 voltage regulators)
HIgh-quality Panasonic electrolytic capacitors
Name brand resistors, capacitors, and LEDs
D-Sub 9 connectors, pin headers, and jumper wires for connecting various scale configurations

To complete the build, you will need to provide a set of compatible Glass or Magnetic DRO scales, a suitable non-metallic enclosure and a 7.2V-9V AC/DC power adapter with a center-positive 5.5mm barrel connector.

Each circuit board is fully electrically tested by the manufacturer. Additionally, I personally program and test every microcontroller, inspect each PCB, and check the kit before shipping it out.

Specifications

Features

Supports four linear axis inputs, tachometer, and a touch probe or tool setter input
Scale inputs can be configured for use with PNP, NPN, and push/pull sensors
Two separate onboard linear voltage regulators provide clean power supply voltages to the 5V scale rail and 3.3V logic rail
Per-scale bypass capacitors filter out transient spikes on the power supply lines

Scale Inputs	4
Tachometer Input	Yes
Probe/Height Setter	Yes
Power Supply	7.2V DC - 9V DC
Current Draw	Approx. 200 mA
Width	2.7"
Length	2.8"

Supported Scales

This TouchDRO adapter supports a wide array of Glass and Magnetic DRO scales, as well as many standard rotary encoders that output a quadrature signal with a 5V level. This includes most, if not all, brands of budget Chinese Glass and Magnetic DRO scales, as well as the vast majority of modern brand-name DRO scales.

To ensure that your particular scales are supported, please refer to their documentation to ensure that the scales use positive 5V power supply voltage and output quadrature signal with a 5V level.

For more information about Glass and Magnetic DRO scales, refer to the pages linked below:

Mechanical Drawings

Fig 1: Mechanical Dimensions

Circuit Schematic

Fig 2: Circuit Schematic

Kit Contents

This DIY DRO kit includes all of the components needed to assemble a TouchDRO adapter.

Value	Description	Qty.	Reference
PCB	TouchDRO Adapter PCB, Immersion Gold plated, Green solder mask, White silkscreen	1	N/A
MSP430G2553	16-Bit mixed-signal microcontroller (pre-programmed)	1	U1
74xx244	SN74HC244 Octal Buffer	1	U1
HC-05	Bluetooth Transceiver, Slave	1	HC-05
LM1117T-3.3	Voltage Regulator, 3.3V 800 mA, LDO	1	LM1117
LM1117T-5.0	Voltage Regulator, 5.0V 800 mA, LDO	1	LM1117
Capacitor, 100 uF	Cap. electrolytic, 100uF, 35V	3	C1, C2, C3
Capacitor, 0.1uF	Cap. ceramic, 0.1uF 50V	12	C4-C15
Resistor, 330 Ohm	Metal film resistor, 330 Ohm, 1/4W, 5%	2	R2, R3
Resistor 47KOhm	Metal film resistor, 47 KOhm, 1/4W, 5%	1	R1
Resistor Network	Resistor Network, 47KOhm, 10 Pin	1	RN1
LED	LED, Green 3mm, 20 mA	2	HB, PWR
Pin Header	Pin Header, 4x1, 1" spacing	5	X,Y,Z,W, HC-05 (optional)
Scale Connector	D-Sub 9 Pin, Female, Panel Mount	4	N/A
Power Jack	2.1x5.5 mm power input jack, PCB mount	1	Pwr

Documentation & Resources

Useful Resources

Port Functions

Fig 3: Input Ports

Port	Description	5V-Tolerant	Note
X,Y,Z,W	Inputs for four linear axes	Yes	Pulled up/down depending on RN1 position
Tach.	Tachometer input	No	Pulled up to 3.3V
Probe	Touch probe input	No	Pulled up to 3.3V
Power	7.2V-9V Power input	N/A	2mm x 5.5mm barrel, center positive
PROG	Programming Port	No	Used to re-program MSP430

Note that the scale inputs on this adapter are 5-Volt tolerant since they are connected to the TTL digital buffer IC. On the other hand, the tachometer and probe inputs are not 5V-tolerant since they are connected directly to the MSP430 microcontroller and will be damaged by voltage exceeding 3.3V.

Axis Inputs

TouchDRO DIY DRO Adapter Kit for Glass Scales supports up to four quadrature axis inputs. During the assembly, the inputs can be configured to work with NPN, PNP, and Push/Pull sensors by altering the location of the pull up/down resistor array.

Tachometer

The board supports non-directional tachometer input with a frequency range of 1Hz to 10KHz. The tachometer input pin is pulled up to 3.3V via an internal resistor; the tachometer should provide a sinking (NPN/open-collector) or push/pull output.

Touch Probe

Touch probe input is a binary on/off input. The pin is pulled up to 3.3V via an internal resistor. The firmware can handle either a normally-open or normally-closed probe. During boot time, it detects the state of the input and assumes that the probe is in the "Off" state; the opposite state will be treated as "On".

Power Input

The board uses a center-positive 5.5mm x 2.1mm power input jack. The on-board voltage regulators can use supply voltage ranging from about 3.6V DC to 12V DC and can work with a range of power supplies. For best results, a power supply should provide at least 200 mA of current and 7.2V to 9V.

A 2-pin "Pwr." header is wired in parallel with the power jack. It provides an option to use a panel-mounted power jack with an inline On/Off switch.

Grounding

Proper grounding is very important for the stable operation of your DIY DRO setup. In order to reduce EMF issues, ground the board to the machine's frame and ensure that the scales' cables are connected to the ground only on one side. Mounting holes on the board are tied to the ground fill, as are all of the ground pins. For more details please refer to the "Avoiding Common DRO Scale Problems" page.