Recently I posted a mini review of the iGaging Absolute DRO Plus scales that covered the some basic information on the connection scheme, etc. As I mentioned in the last post, the scales use a different communication protocol. Unlike the DigiMag scales, these scales require additional circuit between them and the MSP430 LaunchPad board. As promised, in this post I will provide instructions on how to connect the scales to the MSP430 Launchpad controller.IMPORTANT NOTE: There are two versions of these scales, older version "AbsoluteDRO", and newer "AbsoluteDRO Plus". The former do not work with TouchDRO (yet), since they use some unknown data protocol.
Before starting, please confirm that the scales you have are indeed the Absolute DRO Plus version. It appears that there was an older version that uses a slightly different protocol.
As I mentioned in the previous post, the scales use a different protocol and won't work with the "iGaging" version of the firmware. I've since added support for these scales to the "Mixed Scale" version of the firmware (v 0.4 Beta), available on the Downloads page. Additionally you will need to build a very simple adapter board that will pull the data and clock lines up. Below is the list of required parts (per axis):
- Prototyping StripBoard(available from Amazon)
- Two resistors in 47-100 KOhm range
- One or two 0.1 uF capacitors. (read below)
- Some small gauge wire
- Mini-B USB breakout board [optional]*
*These boards are needed only if you don't want to cut the cable (i.e. be able to use the scales with the original head in future). The boards I'm using are sold by Sparkfun.com. Similar boards can be found on Amazon here or here. Both kinds work, just follow the markings on the PCB.
Adapter Board Assembly
In this case the term "adapter board" is used very generously: we are basically adding two resistor between the data/clock lines and the Vcc (positive supply) line. To do so, cut off the Mini-USB plug at the end, strip the wires and twist red and black wires together, as shown in the photo below.
|Relevant wires are stripped and tinned|
With the wires ready, cut a small piece of the strip board. You want to have about 5 holes per strip, 4 stips per axis. The board can be cut by scoring a line through the center of a row of holes on both sides and breaking off the excess using pliers, etc. When the board is ready, sand the copper lightly with some fine sandpaper, wipe it with rubbing alcohol and solder the wires to the board as shown below.
|USB cable soldered to the stripboard|
Next, you will install the pull-up resistors. They can be any value between about 47 KOhm and 100 KOhm. The resistors should be soldered between the green/white lines and the positive supply line.
|Pull-up resistors installed between Clock/Data and Vcc|
Finally, prepare four pieces of wire (for each axis) and solder them to the four lines on the opposite side of the board. Optionally, add a ceramic 0.1 or 0.01 uF capacitor between the Vcc and Ground lines. The finished board should look like similar to the one shown in the picture below.
|Connecting wires soldered to the other side of the board|
Alternatively, if you don't want to cut the cable, you can use a Mini-USB breakout board. In that case, the connections should be as follows:
- "Vcc" -> ground
- "D1" -> data
- "D2" -> clock
- "ID" -> Vcc
- "Ground" needs to be tied to "Vcc", as shown below
|Connecting wire soldered to the breakout board|
|"Vcc" and "Gnd" are tied together|
Now you can connect the breakout board to the adapter. The color coding of the connecting wires is the same as above.
With that said, there is a benefit to cutting the cable: from the factory the cable is shielded, but the shielding isn't connected to anything. By cutting the cable you can ground one side of the shield to the common ground, which should reduce noise in the lines. If you decide to go that route, there two things to keep in mind:
- The shield should be connected to the ground on one side only (preferably to the adapter board
- You will not be able to solder to the aluminum foil, so the connection will need to be mechanical
Connecting to The Launchpad
Pin functions of the MSP430 Launchpad DRO controller are explained in this post from last year. In this particular case you will want to tie all Vcc wires together and solder them to the "Vcc" pin in the lower-right part of the Launchpad. Likewise, tie all ground wires and solder them to the "Gnd" pin in the same corner. Finally, solder white wires to the "Data" pins and green wires to the corresponding "Clock" pins. The finished result should be similar to the one shown in the picture below.
|Finished connection should look similar to this|
The preferred way to connect the adapter boards to the Launchpad is by desoldering the pin headers and soldering the wires in their place. If you're not up for that challenge, you can solder the wires to the pins as well, but I recommend that you use heat shrink tubing on each line to avoid shorts.
Alternatively, you can buy the MSP430 LaunchPad bundle that TI sells on Amazon that comes with wires that have female connectors crimped to the ends.
Reading Head Mod
A number of people has been experiencing random resets with the original iGaging scales, caused by noise-induced voltage spikes in the wires. I don't know yet if these scales will have the same problems (mine seems to much more stable, though). The bypass capacitor on the adapter board will create a path for high-frequency noise to flow to the ground, but as an extra precaution I recommend that you add one in the reading head as well, as shown below.
|Bypass capacitor can be added to the reading head|
As you can see, connecting iGaging Absolute DRO+ scales to the TouchDRO controller is pretty straightforward. If you're not sure where to go from there, take a look at the MSP430 LaunchPad Mixed Scale DRO Controller page for more details. There is a number of useful links at the bottom of the page. As usual, please feel free to post questions and comments below and I will do my best to get back to you ASAP.