Ultimate LRS Resources

This page is for all permanent stuff for my ULRS build


Disclaimer: All of this stuff is not working yet! It’s waiting for the correct ULRS software!

See here:

The current beta version 2.23 doesn’t support the Ultimate LRS mini, but the 2.24 should be released in a few days and will support it.

Errata

  • PPM pin goes to A0 but should go to A3 (in the schematic it’s correct – the bug is in the layout)
  • impedance of HF line could be wrong – need to investigate how to make 50 Ohm lines on a pcb
  • capacitor in the reset line is unclear

Schematic

Schematic as PDF

If you need the original eagle files, just let me know. The board design is based on this breakout board.

Board

Order my first PCB design

Just be warned: I’m no expert in PCB design, I do just just for fun. The board is not “nice” but it works. The component labels could have deserved a bit more love and some autorouter traces could be optimized.

Design goals

  • fit onto a 5x5cm board (cheap build)
  • be easy enough to solder
  • same PCB for ground and air
  • pack everything into transparent heat shrink sleeve (with some cuts for the connectors)
  • I don’t need an RSSI output
  • make the arduino easy accessible with an FTTI cable
  • The failsave button is not on the PCB (there was no space)
  • power everything from 5V (if the OrangeRX modules work with 3.3V powering everything from 5V should be good enough; the 6V gives max power to the TX but adds the pain providing 6V; the original schematic used a voltage regulator, but no reason to burn so much power into heat or add an other UBEC)

Soldering

  1. solder the arduino pins (mine came without), just make sure the angled pins go to the bottom – don’t solder the arduino onto the PCB yet!
  2. solder the RFM23BP – looks more difficult than it actually was
    • the designer of the breakout board soldered the ground shield onto the via pads, I didn’t get this to work (soldering iron probably had not enough heat)
    • if heat generated by the transmitter during operation is too much, maybe put some heat conducting paste between ground shield and PCB – I don’t know yet
  3. solder everything else except the arduino module – order doesn’t make much difference
  4. solder the arduino module

IMG_20160510_141259

Connectors

  • all 4-pin connectors have ground at the corner of the PCB
  • the one next to the antenna is: from antenna to PCB-corner:
    • Failsafe-Button (needs connection to ground)
    • PPM-Input/Output (not tested yet)
    • 5V supply voltage for arduino and RFM23BP
    • Ground
  • the one next to the arduino board: from PCB-corner to arduino
    • Ground
    • Arduino TX
    • Arduino RX
    • Arduino Reset

BOM + Sourcing

I’ve bought all items (except PCB) from aliexpress, the BOM is not too complex. The most important stuff is listed here:

The resistors values (except the 220R for the LEDs) don’t matter that much, they are more for protection. If you have one close by, it should also work. Same for the capacitors near the antenna connector. They are just for buffering and from the breakout boad / reference design.