I’ve been working on designing a .NET Gadgeteer DaisyLink module for a project I’m working on and ran into a limitation of the GHI Extender module that I thought warranted an improvement (aka “hack”). I’ll detail the steps I took to convert a GHI Extender module into a DaisyLink Extender module in this post.
In case you’re unaware of what DaisyLink is…in a nutshell, it’s a way to chain together Gadgeteer modules so that you only have to use a single socket. An example of such a module is the GHI Smart Multicolor LED module. On a DaisyLink module there are two sockets – the upstream socket (the one going toward the mainboard) and the downstream socket (the one going away from the mainboard).
The communication for DaisyLink happens using the I2C protocol and a neighborhood bus. It isn’t the intent of this post to explain in detail how DaisyLink works. For that info, see the .NET Gadgeteer Module Builders Guide. However, I mention this because the neighborhood bus is the reason for this hack. All the pins in the two sockets on a DaisyLink module can be passed straight through from one socket to the next except the neighborhood bus (socket pin #3). This pin has to be activated/deactivated independently as this is the mechanism that the mainboard uses to identify which module it is communicating.
The GHI Extender module is in my opinion the most useful of all Gadgeteer modules since you can basically do anything with it. Before I started understanding how DaisyLink worked, I always assumed that the Extender module had two sockets on it so that it could be used to develop DaisyLink applications since I otherwise see no application for the other socket except as a way to tie two cables together. The pins on the two sockets are directly connected together and to a header on the edge of the module. As I mentioned above, this is a problem since I need to be able to control the value of pin #3 independently on each socket. So, it’s time to pull out the soldering iron!
If you flip the Extender module over and rub the solder mask a little to polish it, you will see the circuits. I’ve highlighted in green the circuit for pin #3 that goes to both sockets and to the header pad. Note that the left-most junction is where the circuit connects to what we will refer to from now on as the downstream socket. We’re going to add an additional pin to the header called “P3*” (since * is used by Gadgeteer to denote downstream sockets) and make the header labeled “P3” only connect to the upstream socket pin #3.
We’ll begin by using a box cutter or Xacto knife to scrape the solder mask off the circuit on both sides of the junction we want to bypass.
Next, we’ll use the box cutter to make four deep cuts through the copper circuit we just exposed and then we will remove the sections. The cuts to make are shown in red on the picture to the right. Remove all the copper between each set of parallel cuts.
Now that pin #3 of the downstream socket has been isolated, we need to connect the two circuits that we just cut back together so that the upstream socket pin #3 will be connected to the “P3” header. Start by using the box cutter to scrape a little more of the solder mask off the copper on the right side of the top circuit we cut and below the bottom circuit we cut. Now, take a thin wire and solder it to the two pieces of exposed copper. If you have some Kapton tape to stick down the wire while soldering, it will make it a lot easier. However, you can manage it w/o if necessary. It also helps if you tin the wire with some solder before attempting to connect it to the PCB. You will probably not get a large bead of solder to stick to the tiny piece of copper. As long as you get enough so that the wire is secured that will be sufficient.
We’re done on the back side of the PCB. Next we’ll attach the male headers to the board. Although the module has 10 header holes, we will need a section of header that has 11 male pins. To make it easier to solder every square, put the header into a spare breadboard and put the Extender module on top. I also like to put an extra piece of header underneath the module on the other side to give it some support and help ensure it stays flat.
Take a small piece of thin insulated wire and strip a very small amount off one end and tin it with some solder. We’ll solder this to pin #3 of our downstream socket. Note that in the picture on the right, pin #1 is in the bottom left corner of the socket. All the even numbered pins are in the top row and the odd numbered pins are on the bottom row. So, pin #3 will be the second pin on the bottom row. It will greatly simplify soldering if you have a tiny alligator clamp that you can clamp the wire to the PCB so that the exposed end of the wire is lying on top of the pad for pin #3 as is shown in the picture. If you have a flux pen, it would be a good idea to add a little flux to the SMD connectors before soldering. However, if you take care and get it done in one heating you should have no problems w/o additional flux. Use your soldering iron to heat the wire and pad so that the reflowed solder connects the two together. You may need to add a tiny amount of additional solder. Just be careful not to bridge any of the other pads. Solder the other end of the wire to the extra header pin.
Finally, to help protect the uninsulated wire we added to the bottom side of the board I created a label in Excel and printed and taped it to the underside of the board to help label the extra header in case some day years from now I forget why it’s there.
Now that I have a good way to prototype, it’s time to go finish my new DaisyLink module! Thanks for stopping by.