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Mr.RC-Cam

MP Select Mini 3D Printer External Antenna Mod

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Last month (Feb 2019) I purchased a refurbished MP Select Mini V1 3D Printer for $89 USD (with free shipping).  The flash price quickly ended, sold out.

270031.jpg

After the unboxing I found that mine was new (not refurbished). But I had to replace the extruder's cooling fan because it was too noisy. Monoprice did not respond to my email request for a replacement part. Fortunately I had a 12VDC 30mm fan that fit, so problem solved.

I quickly discovered that WiFi connections were unreliable. For the record, it works fine when the printer is close to the router in my living room closet. But I need to print elsewhere. And the short range is understandable because the WiFi antenna is inside the printer, surrounded by the heavy sheet metal case. The solution is to convert the printer to use an external antenna.

Before I talk about my antenna hack, I would like to point out that there is a fantastic wiki site that discusses a variety of mods for this printer. It includes instructions on how to enable WiFi connectivity, which is a hidden (unadvertised) feature of the V1 printer. I recommend that all MP Select Mini owners bookmark the Wiki: https://www.mpselectmini.com/start

With all the formalities out of the way it's time to talk about the Wi-Fi antenna modification. Let's start with some fine print.

It's not a hack for the typical mortal. Things to consider:

  • It voids the warranty. Blame only yourself if things don't go as planned.
  • Altering RF circuitry is not like working on a traditional DC circuit. In the RF domain *everything* matters.
  • Good SMD soldering tools and PCB rework experience is a prerequisite.
  • This hack is difficult/risky so proceed with caution. You've been warned.

Before you start the modification, first confirm that your printer's WiFi is working. I shouldn't need to say this since the mod is for users that are unhappy with the RF range they are currently getting. But some hackers like to do mods just for the sport of it, so that's the reason for advising to fully test it out before any hacking.

 

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You'll need a 6-inch (15cm) long RG316 coax cable with SMA receptacle connector. For convenience I suggest purchasing a RG316 SMA extension and cutting off the plug end. Like this:

rg316_ext_500.jpg

 


Also needed is a SMA equipped 2.4GHz omni dipole antenna with +2dBi to +3dBi  gain. Avoid those cheap Chinese antennas, they often have reduced RF performance.

ant2400_flx_400-01.jpg

By the way, you can use RP-SMA connectors instead of traditional SMA.  But never mix RP-SMA with SMA.

 


Disassembly:

  1. Remove the left side panel (5 screws) and the bottom panel (6 screws). Pry off the menu knob.
  2. Remove the rotary encoder board (4 screws) and transparent LED lens insert (2 screws).
  3. Remove the LCD bezel trim screws (4 places).
  4. Remove the front bezel trim. There is some hidden sticky tape holding it down, so slowly pry it off to prevent damage.
  5. Unplug the two I/O cables. Pull out the LCD board.


Note: The existing antenna is a PCB microstrip located on the LCD PC Board. See image below. We need to cut it away and then add the external antenna.

PCB_Antenna1_800.jpg

 

PC Board Copper Trace Cuts:

  1. Use a sharp knife and scratch off a small rectangular area of solder mask near C17 to expose the copper ground plane. Solder tin the GND area.  See photo below.
  2. Use a sharp knife and CUT the Antenna's feedline trace from the C7 coupling cap. See photo below.
  3. Use a magnifier and visually inspect the CUT. Next use an ohmmeter and confirm it's no longer electrically connected to the nearby pad on C7.

AntMod1_1000.jpg


Coax Installation:

  1. The RG316 coax is prepped (cut signal and shield, pre-tin conductors) and then soldered to the PC board. The center conductor goes to C7 and the shield goes to the GND area created in the previous step. See photo below. Note: The 6-inch length is long enough to reach the left side panel. Avoid longer coax lengths to minimize RF signal attenuation.
  2. Thoroughly clean off the flux residue.
  3. Add some hot melt glue to strain relieve the coax. Do this away from the RF circuitry; The open area between C15 and R9 is a good place.
  4. When you re-install the LCD board just pass the coax (with SMA receptacle connector) through the existing opening that is used for the board's two I/O connectors. No need to cut or drill the LCD's mounting bracket.

AntMod2_1000.jpg
 

Antenna / SMA Mounting:

  1.  Mount the SMA connector on the front-left side of the metal base. You can drill a hole in the metal panel, but I printed a new side panel instead. The location of the SMA connector is shown in the photo below.

AntMod3_800.jpg

 

Validate the mod:

  1.  Test it out. You should notice that WiFi range is dramatically improved. If not, then you've made a mistake; Check your work again.

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