TouchDRO Quadrature board is designed to interface standard quadrature scales to TouchDRO Android application. It supports up to four scale inputs, directional tachometer, and touch probe input. All inputs are buffered and 5V-tolerant. Scale inputs can be either single-ended, or differential (for better noise immunity).
The controller is compatible with majority of glass and magnetic scales currently on the market (up to 1um resolution), as well as many optical and magnetic rotary encoders with standard 5V RS422 output. Some of the compatible brands include Ditron, Easson, DRO Pros and many others.
Refer to your specific scale's manual to ensure that it outputs either single-ended or differential quadrature signal.
TouchDRO Quadrature adapter can be purchased in three different packages from the "Pre-Made Boards" page.
As the name suggests, this package consists of the assembled, programmed and tested board. In order to complete the setup you will need to provide power supply, plastic enclosure, and optionally scale connectors and hook up wire.
Board with Connectors
In addition to the assembled board, the kit includes four female D-Sub (DB-9) connector and 6 ft. of hookup wire (six colors, 1ft each). To finish the setup you will need to provide a DC power supply and a plastic enclosure.
The kit includes an assembled, programmed and tested TouchDRO board, four wiring harnesses, and four D-Sub DB-9 female housings.. The harnesses have a 2x4 female connector on one side, and pre-crimped D-Sub female pins on the other side. To connect the scales you will need to identify correct pin positions (from the scale's manual) and push the pins into the housing. To complete the setup you will need to provide a power supply and a plastic enclosure.
The kit is a good option for someone who isn't comfortable with soldering, or simply doesn't have the required tool. It is also more convenient in general, since the wires aren't soldered to the board and can be plugged/unplugged for easier mechanical assembly.
|TouchDRO Quadrature Adapter Pin Functions|
|TouchDRO Quadrature Adapter Dimensions|
Assembly and Installation
TouchDRO board uses a common 2.1mm x 5mm round DC power jack, similar to the one used by the Arduino boards, therefore any power adapter that provides 7-13V 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. The transformer provides mains isolation, thus eliminating a noisy ground loop.
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.
Axis Input Pin Functions
Inputs for the scales are located along the left edge of the board, with first axis (X) on the top and last (W) at the bottom. Each connection 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, they will be pulled down to the ground and the readout will still work as expected. If the scales support differential output, it's recommended to use all four channels for better noise immunity. Otherwise the exposed pins of the unused wires need to be isolated to prevent them from shorting something out.
Majority of the scales on the market use a standard DB-9 female connector (AKA 9 pin D-Sub). If you purchased a "No-Soldering Kit" or "Board + Connectors" kit, you already have the correct connectors. In the former case all that's left to do is to identify the right pin positions, push the pins into the housing, and plug the harnesses into the board. Otherwise you will need to solder the wires to the connector and to the board. Alternatively, you can skip the connectors all together and solder the scale cabled directly to the board.
|Pins can be slipped into the connector body rather easily|
To identify the correct pin positions, refer to the scale's manual. I should either provide an illustration, or a list of pin assignments.
|Some scales have pin functions etched on the body|
D-sub connector pin number go from left to right, top to bottom on a male connector with wider part at the top and pins facing the viewer. Since in this case we are dealing with female connector, position it with the back facing you and wider side on top, and either push the pre-crimped pins into the identified hole, or solder the wires to the pin.
|Female (back) and male DB-9 Connector|
Important note: once the pins are pushed in, extracting them will require a special tool, so make sure that you are pushing the pins into right positions.
Probe and Tachometer Connections
Touch probe and tachometer share the six-pin header alongside the bottom of the board. Pin functions are as shown above. Please note, the header provides 5V and 3.3V Vcc at the two left-most pins. Since 5V is lethal to the microcontroller, care should be taken not to short those pins together, otherwise the controller will be permanently damaged.
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 either 3.3V or 5V (depending on your particular sensor), A and B output, and Ground. If B is not connected the tachometer will be non-directional.
Note: there are some rotary encoders that provide open-collector (also called NPN) output that need additional parts to adapt to the board. Namely, the pins need to be pulled up to Vcc via 5K resistors.
Inexpensive touch probes and tool height setters work similar to a simple electrical switch. Depending on the configuration, when the probe touches the workpiece it either opens the circuit, or closes it (normally-closed or normally-open, respectively). TouchDRO board supports (and automatically detects) both flavors.
Connecting a probe should be pretty straight-forward: connect one side of the switch to Vcc (5v or 3.3V) and the other to the probe pin. There is one nuance: some probes have an LED. If that is the case, it has to be reverse-biased (backwards), 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.
Reset Button (optional)
A useful feature of the Quadrature Adapter is the ability to reset machine origin without powering off the board. This is done by resetting the microcontroller. To add this feature you will need to connect a normally-open momentary switch between the reset pin on the programming header and the ground.
The board is equipped with four status LEDs, as shown in the picture.
- Green - power
- Amber - 1Hz heart-beat
- Read - touch probe (on when probe is engaged; off otherwise)
- Blue - bluetooth
Once all connections are complete, it's time to power up the board. If things go well, green LED will light up almost immediately (there might be a faction of a second delay while the capacitors are charging). A few milliseconds later amber LED will start blinking at a steady 1HZ rate (once per second), indicating that the microcontroller is working.
At the same time, depending on the state of BlueTooth transceiver, blue LED will be blinking in one of three following patterns:
- Board not paired - two pulses per second
- Board paired but disconnected - short pulse every 2 seconds
- Board connected - two short pulses every 2 seconds
At this point the board can be paired to be paired with the tablet and TouchDRO will be ready for the initial setup and calibration. Please refer to this post for details on how this is done see the post "DRO Scale Calibration". Additionally, TouchDRO YouTube channel has some videos on this subject.