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Building an AUX-port Ethernet Dongle for use with Celestron telescopes

This is a photo documentary of assembling an Ethernet Dongle to interfaces with Celestron telescope mounts. Ethernet provides identical functionality to "WiFi" here, except it is much more reliable and not prone to drop-outs in the middle of a night session.

See this thread on Cloudy Nights for more information.

First step: flash the ethernet sketch (program) into the Arduino. With a Pro Micro board, simply use the built-in USB port for this. But here, we are using Pro Mini boards, so an external 5V TTL serial adapter is used.Normally, the Arduino would have the six-pin header (shown) soldered in place, but we don't want that here (it gets in the way).
Instead, insert the header into the end of the TTL programming cable as shown.
Now stick the header through the underside of the Arduino Pro Mini. Make sure the six wires are in the correct order. In my set-up, the Orange wire happens to be "DTR" from the serial adapter, so I have ensured that it mates up with the pin labelled "DTR" on the Arduino. The colours of other cables will be different from this one.
Lay the assembly down as shown, and lightly apply pressure to the Arduino/header so that it makes contact. Keep a finger on it while uploading the program to it from the Arduino IDE.
Begin the project assembly, by stacking three layers of 3M black mounting tape onto the ethernet module: one layer between the RJ45 jack and the W5500 chip, and then two more layers on top of that and the chip. This creates a flat surface onto which the Arduino board can be placed. But first, add a bit of electrical tape over top of the silver crystal as well, to prevent short circuits.
Top view of the mounting tape and crystal with translucent electrical tape on it.
Here is the Arduino Pro Mini board (5V/16MHz) stuck on top of the mounting tape. It has deliberately been placed off to one side, so as not to overly obstruct the wiring points for the ethernet module underneath at top right.
Now stick more mounting tape to the flat side of the DC-to-DC buck converter, which one should already have adjusted for 5.8V output. If not, it may fry the Arduino board later when first powered-on.
Stick the DC-to-DC buck converter on top of the Arduino, being careful not to obstruct any of the signal holes, and also avoiding the (red) reset switch area.
This is what it looks like once all stacked together with 3M mounting tape.
Solder the small "mode switch" to this side of the RJ45 jack. This step could be done even earlier if desired. Use flux, and try not to overheat it to the point where the switch innards melt! I run my soldering iron at 330C for most things.
Now begin to wire the ethernet module to the Arduino. Begin with a solid wire straight down from Arduino Pin-10 to the SCS (or CS) chip-select signal of the ethernet module. This will also act as a support post, making the assembly much stiffer and more rigid.Then begin to add the extra signal wires, starting with the orange one shown here. It is easiest to complete that entire first row of five holes on the ethernet module before attaching wires to the second, outer row of five holes.
Finish adding all of the signal wires to the ethernet module, and then also run power to it and the Arduino from the Buck converter. Here, RED is the Buck output, and BLACK is GND.The mode switch also gets wired now, by soldering the bottom pin to the side of the RJ45 or to any other convenient GND point. The middle wire is connected (GREEN) to Arduino Pin-8.I have added a bit more translucent electrical tape between the switch and the RJ45 jack after doing this, to prevent future accidental shorts there.
Another view of the fully wired ethernet/Arduino combination. Note that I used thicker wire than necessary for some of the power connections. The skinny stuff would have been fine everywhere.
Top view of the ethernet connections.
Bottom view, showing the INC and NC pads with no wires attached -- those don't get used in this project. Also notice how all of the protruding pointy bits have been snipped flush on everything on the underside. This way they won't stick through the heat-shrink tubing when it gets added in the final step (much later).
Overview of everything accomplished thus far. At this point, the module is ready for early testing, if desired. Connect +9V or +12V to the Buck converter -- you may have to temporarily solder wires on to accomplish this. When powered, several RED LEDs should light up immediately. If not, then disconnect the power and search for wiring errors on the RED and BLACK wires. To test it further, power it off, ensure the "mode switch" is in the UP ("off") position, and Connect an ethernet cable between the module and a computer, and then power it back on again. If all is working, the computer should "connect" to this "new network" and be assigned an IP Address of If not, then something is not wired correctly.
Now to wire up the AUX port interface. Begin with the diode, stripe DOWN, into the TXO hole on the Arduino board. Then a 51K-ohm (give or take) resistor into the Vcc hole on the opposite edge of the Arduino board. Twist the resistor around the stiffer diode lead, and solder all three connections.
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