Mixed Scale Controller DIY DRO Kit is designed to simplify the build process of the "Mixed Scale" DRO controller. As the name suggests, this version of the controller comes as a do-it-yourself kit that consists of a bare printed circuit board, MSP430 microcontroller pre-programmed with the "Mixed Scale" firmware, BlueTooth transceiver, and all of the necessary parts to build the voltage shifter circuit. The board is primarily designed to run the Mixed Scale firmware and interface with 1.5V and/or 3.3V scales and calipers, but can be easily tweaked to work with quadrature encoders instead.
Compared to building a controller on a breadboard, the main benefit of this kit is the professionally designed and fabricated circuit board. Quite obviously, it's much more convenient to assemble a controller on a pre-made circuit board. More importantly, though, the end result will likely be much more stable and reliable, since the PCB is carefully laid out to minimize the effects of noise.
|Finished Mixed Scale DRO Controller|
- Provides input for up to four axis, directional tachometer and touch probe.
- Supported protocols include:
- Sylvac Protocol (48-bit) used by the common "Chinese" scales
- 21-bit protocol used by Shahe, iGaging DigiMag remote DRO, and AccuRemote scales
- BIN6 protocol used by most Inexpensive digital calipers
- Each scale input can be independently configured to use either 3.3V or 1.6V power supply
- Clock for iGaging scales can be provided to each scale individually using a jumper setting.
Please note, the controller can't be used with a mix of capacitive and quadrature DRO scales at the same time. The board is pin-compatible with quadrature firmware, so if at a later time you decided to upgrade the scales, the chip can be re-flashed with quadrature firmware. Since the board doesn't have a 5V regulator, a small hardware mod is required as well: two resistors need to be removed and 5V from a power supply will need to be connected to a pin so it can be routed to the scales.
- Professionally fabricated PCB
- Pre-programmed MSP430G2553 microcontroller (with a socket).
- HC-05 BlueTooth transceiver
- 3.3V low-dropout voltage regulator
- LM339 comparators (2)
- 47 KOhm resistors (17 )
- 4.7 KOhm resistors (8)
- 220 Ohm resistors (5)
- 0.1 uF ceramic capacitors (9)
- 100 uF electrolytic capacitors (3)
- 2.1mm x 5mm power jack
- 2x3 pin headers (4)
- 2x4 pin header
- LEDs (1 each, Red, Green, Amber)
You will need to provide a power supply that can provide between 5V and 13V, and a plastic enclosure.
- Calipers and Sylvac-type scales can easily be damaged by 3.3V supply, so make sure the jumper setting is correct before connecting the scales.
- Probe and tachometer pins are connected directly to MSP430, therefore if voltage over 3.6V is ever applied to them, even for a brief moment, the microcontroller will be permanently damaged.
- The frame of iGaging Remote DRO scales is connected to the ground, while calipers and Sylvac scales are connected to Vcc. If you intend to mix the two types of scales, ensure that they are insulated from each other or you will blow up the voltage regulator on the board, and possibly explode the electrolytic capacitors.
- Voltage regulator can be pretty hot and burn you, especially if the input voltage is close to 13V. If available, use a power supply that is as close to 5V as possible to keep the regulator cool.
Scale inputs are located along the left edge of the board (as shown in the picture). The pins are labeled +, D, and C for Vcc, Data and Clock respectively. The last [unmarked] pin is Ground.
The board can work with directional (quadrature) and non-directional tachometer input. The pins are connected directly to the microcontroller and have internal pull-down resistors enabled.
Warning: These pins are not buffered, so care should be taken to not exceed the 3.6V maximum rating for the microcontroller.
Touch Probe Input
Touch probe pin is located on the same header as the tachometer input. The controller supports normally open and normally closed probes, which will be detected at the startup.
UART output header is located on the top edge of the board (close to the middle). The pin sequence matches that of a standard 4-pin HC-05 module, so one can be soldered directly into the board.
In-Circuit Programming Header
This header, located to the right of the UART header, can be used to program the microcontroller using either the MSP430 Launchpad or a dedicated ICP device.
Scale Voltage Selection
Each scale input can provide either 3.3V or 1.5V to the scales. The voltage is selected using a jumper setting on the appropriate header as shown below. The same settings provides a reference voltage to the comparator.
The board supports different input modes (open drain, line driver and push-pull) that require either pullup or pulldown resistor, which can be configured using the resistor selector jumper setting for each scale individually.
For most capacitive scales, except iGaging AbsoluteDRO+, pull-down resistors should be used; additionally pull-up mode might be useful for rotary encoders, etc.
Please note, using pull-up resistor for 1.5V scales will damage them, since the resistor pulls the line up to 3.3V.
iGaging DigiMag Remote DROand AccuRemote scales require external clock signal that is provided by the microcontroller. The clock signal can be connected to each scale using the "Scale clock" header. To provide clock signal to a scale, install a jumper on the corresponding pair of pins.
Make sure the clock is disconnected when 1.5V scales are used, or the scale will be damaged by the 3.3V signal coming from the controller.
The board has three LEDs that indicate its state. Their functions, from left to right are:
- Touch Probe Activated - the LED will be lit when the touch probe is activated.
- Status/Heartbeat - the LED indicates the status of the board. During startup initialization the LED will blink rapidly for about one second while the board is detecting scale protocols and probe state. After that it will blink at 1HZ rate (once per second)
- Power - the LED will be lit when the board is powered on
The kit comes with a standard 2.1mm x 5mm power jack, same as many of the Arduino boards. The on-board voltage regulator can accept from 5V to 13V and convert it to regulated 3.3V. It's better to go with lower input voltage to keep the regulator cool, otherwise a heat sink might be need.
If you indend to use the kit with Quadrature scales, the power supply should be regulated. Most scales on the market can handle a range of voltages from 5v and up (check the manual for your particular scale).
The Mixed Scale TouchDRO controller kit is a versatile and cost-effective do-it-yourself DRO controller that provides a lot of flexibility. By default it works with most capacitive scales and calipers, providing reasonable refresh rate and excellent noise immunity, and with a few tweaks can read quadrature scales. Compared to the same circuit built on a prototyping board, the kit offers much better resistance to interference, reliability and convenience. At the same time the cost of the kit is not that much higher than what you'd spend buying the components separately, especially given that the kit comes with name-brand parts procured from reputable suppliers.