I’ve been receiving an increasing number of requests to post some build instructions for the digital readout controllers. While working on the step-by-step guide (and building a unit in process) I got sidetracked and ended up designing a controller that can read multiple scales. Even though that project still requires some work I decided to update the basic version of the readout controller to be pin-compatible with the new version.
In this post I will concentrate on the MSP430 Launchpad DRO controller that can read up to four iGaging scales using the middle-of-the-road build described in the Parts List for MSP430 Digital Readout post.
In future, if you decide to add non-iGaging scales the only change you will need to is to add the buffer board between the scales and the Launchpad and upload new firmware.
Step 1 - Remove the Headers
The new revision of MSP430 Value Line Launchpad ships with the 0.1” headers installed. It’s possible to solder the wires directly to the pins but to keep things neat I prefer to remove the headers altogether. This is much easier to do if you first remove the plastic that holds them together. To do so I simply cut it in a few places and them using a hobby knife of a sharp screwdriver to pry the pieces out.
|Using a pair of clippers, cut the plastic in a few places|
Once the plastic is gone flip the board over and desolder the pins one-at-a-time.
|Once the plastic is removed the pins are much easier to desolder|
Tip: when desoldering the pins keep your hands suspended and when you see the solder melt, quickly hit the hand with the board on the table. The pin should fall out and leave a clean hole.
|The LaunchPad is ready for the next step|
Step 2 - Prep the Scale Connections
Tip: Keeping the cable intact can be handy if you want to use the remote readout display that the scales came with (for troubleshooting, for example).
Option A - USB Breakout Board
If you have decided to use Sparkfun’s Mini-USB breakout boards, now is a good time to solder the leads to them, otherwise skip to option B.
I used the wires scavenged from an old USB cable to keep consistent color scheme. The easiest way to get the wires out is to cut a slit along some length of the cable and peel off the outer isolation. Inside you will likely find four wires: Red, White, Green and Black that carry Vcc, Clock, Data and Ground respectively. The holes on the breakout board are marked Vcc, D-, D+, ID and Gnd. D- in this case corresponds to the clock like and D+ is the green data line.
Tip: Tinning the stipped end of the wires makes the assembly easier and reduces the risk of stray strands creating shorts.
|The connection follows the USB standard wiring|
To keep the setup neat I chained the common connections (V+, Clock and Ground). This requires inserting two wires into one on two out of three breakout boards. As long as the wires are fairly thin this should cause any problems. Alternatively you can solder the wires as shown in the picture below.
|Vcc, Ground and Clock can be connected as shown to keep the setup clean|
Option B - Direct Connection
The easiest way to connect the scales to the board is, of course, to directly solder the wires. To do so, remove about 2" of the outer isolation and strip a quarter of an inch off each wire.
Tip: to make the set up a bit more robust drill the holes in your DRO enclosure, thread the cut cables from the outside and tie a single knot. This will prevent the cables from being accidentally torn out.
Step 3 - Connect The Power
There are a couple of Vcc and Ground connections available on the Launchpad board. Since on this unit the USB boards are on the right it’s most convenient to use the pins in the lower right corner of the board. If you followed Step 2.A you should have a read Vcc and a black Ground wires that should be soldered to Vcc and Gnd respectively, connected to the ground
|Vcc and Power connected to the LaunchPad|
Otherwise you will need to solder the tree Vcc and three Ground wires together. This is a bit easier if you first twist them together first.
Step 4 - Connect the Clock Lines
On this version of the controller Pin 1.7 provides clock to all connected scales so all three white wires need to be soldered to it. Unless you are using a heavier wire than what comes in the USB cable they should fit fairly easily.
|All three clock lines are connected to P1.7 (clock out)|
Step 4 - Connect the Data Lines
The green wires are soldered to pins 2.3, 2.4, 2.5 and 2.7. These are the “data-in” lines for the Z, Y, X and W axes respectively. Please note, P2.7 is marked XOUT on the board since it’s duplexed with the external crystal output on MSP430G2553 chip.
|Data lines X,Y, Z connected to P2.3 - 2.5 respectively|
Step 5 - Connect the Bluetooth Transceiver
The Linvor module needs three connections: Vcc, Ground and Rx. I’m using a piece of three-conductor cable scavenged from a hobby servo that use Red, Brown and Orange for those lines.
|A standard servo cable soldered to the Bluetooth module|
Note:Servo cables come in two common color schemes: Black/Red/White and Brown/Red/Orange corresponding to Ground/Vcc/Data.
New version of Launchpad has both Tx and Rx lines marked as “UART” since the new “G” chips have them flipped. Regardless of which version of the board you have, Linvor’s Rx pin needs to be connected to the Luachpad’s Tx (pin 1.2).
The Vcc line can be soldered to the nearby Vcc pin but there is no Ground pin on this side of the board. You can either run a longer ground wire around the board to the Gnd pin in the lower right corner or scrape of a bit of the solder mask and solder the wire to the ground plain.
|The "Rx" line is soldered to "Tx" pin on the LaunchPad|
Step 6 - Add Bypass Capacitors
This step is completely optional but to be on the safe side I prefer to add 0.1 uF capacitors between each scales Vcc and Ground. Since the pins are too thick to fit into the holes with the wires already inserted, so I soldered them to the bottom pads (ala surface mount).
|Optional bypass capacitors between Vcc and Ground|
At the end of this process you should end up with a unit that looks something like the first picture. This is a good time to dust off a multimeter (if you own one), plug in the board and make sure that the breakout boards and the BT module are getting power etc.
The board is now ready for the firmware that is available in the “Downloads” section.