MSP430 Launchpad requires almost no additional parts When selecting a microcontroller [board] for the digital readout project I overlooked the Launchpad in favor of an Arduino board. Earlier this year, though, a reader asked me to help him with a project that required reading a scale running 1.5V. While looking for a suitable hardware to read those scales I decided to try one of the MSP430 Value Line Launchpad kits I had sitting in the closet and realized that MSP430 microcontroller works very well for interfacing with Grizzly iGaging scales as well. First of all the MSP430 Launchpad board is much cheaper than an Arduino, selling for $10, including shipping, at TI’s store (until recently it sold for an incredible $4.50). Second, the microcontroller runs at 3.3V and has built-in pull down resistors, so there is no need for any additional resistors. Finally, it will let me easily add support for 1.5V “chineze calipers” in future. When my new X3 mill arrived from Grizzly I fitted it with a DRO controller using the new MSP430 design. After initial testing and debugging I posted the source code to the Downloads section but never got around to writing decent build instructions. Recently several readers emailed me directly and left comments on the blog asking to post detailed build instructions for the unit. In the next couple of posts I will go through the parts list, assembly and firmware in detail, while building a unit. Required Parts MSP430 Launchpad V1.5 has some subtle differences As I mentioned before, the Launchpad requires virtually no additional parts, besides the scales, a Bluetooth module and some sort of enclosure. Quite obviously you will need a MSP430 microcontroller. The code I’m using is designed for the MSP430G2553 version of the chip, the main reason being the presence of hardware UART implementation and a larger number of pins. This also happens to be the chip that comes installed in the current version of MSP430 Launchpad board. Linvor BT Transceiver mounted on a carrier board To communicate with the Android application you will need a serial-to-Bluetooth adapter (AKA Bluetooth modem). A Linvor HC-0x module from eBay works quite well as is now readily available from US sellers. Please keep in mind, though, that there are several different version of the Linvor module. They all look almost identical but come with different firmware. Version HC-03 and HC-05 can be used either as a master or a slave while HC-04 and HC-06 are preset from the factory into one of those modes. When shopping for an adapter for this project please make sure you get a slave device, preferable mounted on a carrier board (as shown in the picture). To power the whole thing you will need a 5V power supply. The easiest way is to go to your local thrift store and buy a phone charger (one that comes with a mini USB connector). I get mine at a Goodwill store nearby for about $3/piece as there seems to be an unending supply of Motorola-branded chargers. Finally you will need some wires to connect the pieces together. If you don’t have neat spools of wire hanging over you workbench (or some other similar setup) simply cut open an unneeded USB cable and you’ll be set. If you are on a strict budget this is all you will need. The total cost of the whole build adds up to $27.96. If you already have a phone charger and a cable to scavenge you’ll spend even less. Finally, if you forego the carrier board for the linvor module you can get the expenses to under $20. Bill of Materials TI MSP430 Value Line Launchpad kit $9.99 Bluetooth Transceiver $12.99 or Serial-to-USB adapter $9.99 Sacrificial USB Cable $1.99 USB Phone Charger $2.99 Optional Parts Although not strictly required Sparkfun USB Breakout boards make the job a bit neater Unless you want to simply cut the USB cables supplied with the iGaging scales and solder them directly into the board, you will need to get a set of suitable connectors. I personally prefer 4-pin DIN, like the ones found on S-Video cables, connectors as they are readily available locally and provide mechanically-reliable connection. In other words they don’t fall out of the sockets at a most inconvenient time. If cutting cables is not your idea of fun pass time you’ll need 3 mini USB sockets. One approach is to use the Sparkfun’s “Mini USB Breakout Boards”. They are quite inexpensive and almost alway in stock at sparkfun.com. Alternatively DigiKey sells a pre-made cable “Mini USB Buccaneer” for around $9 that is a bit easier to mount to the enclosure than the breakout boards. Since I already have a set of the breakout boards I will stick with them but will include instructions for both approaches. The total cost of this build (excluding the scales and the enclosure) is as follows: Bill of Materials TI MSP430 Value Line Launchpad kit $9.99 Bluetooth Transceiver $12.99 Three of Sparkfun’s Mini USB Breakout Boards $13.39 (including shipping) Sacrificial USB Cable $1.99 USB Phone Charger $2.99 Grand Total - $41.35 Even More Parts The parts listed above will yield a perfectly acceptable DRO controller but the controllers I use in my garage have a few more upgrades that are worth mentioning. The controller I use in the garage has some upgrades. Although the price is more than doubled, the unit is much more rugged and noise-tolerant The first one has to do with the fact that iGaging scales, in essence, read only the relative position and the “0” point is the point where the scales were first powered up. A short period of time after the power to the scales is cut off they lose their position and start from “0” next time they get “juice”. Since I often work on a given part for several evenings or even weeks (and “memorize” a number of positions in process) losing the workspace reference was more than a minor annoyance. The solution to this problem was to provide backup battery power to the scales when the controller is turned off. The whole mod requires a battery holder for two AA or AAA batteries and two diodes: one to stop the 3.3V from going into the batteries when the board is powered up and one to prevent the batteries from powering the board and the modem. Second, to reduce the electrical noise and voltage drops I added a decoupling capacitor between Vcc and Ground across each of the three female connector, and a 2200uF electrolytic capacitors across the power supply. Bill of Materials Battery Holder $3.99 (or less) Capacitors $5 (or less) Neither of the extra mods is required. On the other hand I had some issues with the first [Arduino] version that seemed to be caused by the electrical noise around my old X2 mill. Although I haven’t tried this hardware without the mods so I can’t really be sure that they made the difference, the unit has been working very reliably and hasn’t had any glitches. Conclusion A basic DRO controller using MSP430 Launchpad board can be built for around $45 or less (with some careful shopping). Alternatively, for a bit under $60 you can have one with battery backup for the scales and better noise protection. In the next post I will provide detailed build instructions, so please stay tuned.