DIY DRO Adapter Kit for Glass Scales
Description
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-ended1 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
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
Useful Resources
Port Functions
| 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 | ESP32 Programming Port | No | Used to re-prgam 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.