Anyone tried Laird RM1XX modules?


hi Charles, relax .. i've been all day trying to get a gps readout on the rm186 :wink:

- program the I2C interface

- program the GPS module

- program the RM186

- finally Lat and Long


So much hardware for blinking 2 leds :wink:

I'm kidding you of course ...


@BWhitten Goodmorning, I have a question.

I build the I2C-GPS example from this application note.

' we use the I2C-GPS NAV module to communicate with the GPS receiver using I2C. This module parses the UART output from the GPS receiver and stores the data to be retrieved by the RM1xx using the I2C bus. '

  • I2C output level of this I2C-GPS module is 5 v , is that allowed with the RM186 without level conversion ?
  • What is the advised value then for the I2C bus pull up resistors ? (4K7 works fine)

- What's the function of the 2 resistors on the dev kit between the SDA/SCL lines when arduino selected ?

(Jose Marcelino) #128

I don't know the I2C-GPS NAV module but If you're sure it doesn't have any pull-ups to 5V you can pull-up to 3V and should be OK. I've seen it done in nRF51 projects though the success depends on the I2C/GPS module accepting lower voltage signals.

560Ω... seem to be serial resistors, used to protect the bus against overcurrent.



Yes I mounted pull ups on the bus, on the 'dev hat' :sunglasses:
my main concern was that the I2C-NAV module is a 5 v device, so the level of the I2C signals is 5 v !

I'll have to finish that RTC module, thats a 3v3 device, so I can see the difference.
I never seen those I2C serial resistors in the 'arduino world'

2 laird devkit 'hats .. after a long time discovered I had to cut a trace on this type expi board.
that's why I ordered some different expi boards.

(Jose Marcelino) #130

If you connect your pull-up resistors to 3.3v that's what the bus operates at, since the slave device will only be driving it low to 0v - i.e. signals won't go above 3.3v.

The only problem is if your GPS-I2C device doesn't register the 3.3v signals as valid, but I think this will work because I2C (pulled up to 3.3v) is a common way of connecting a Raspberry Pi to a 5V Arduino without logic level conversion and I see the converter is basically an Arduino.

Just make sure you're not pulling up to 5V anywhere!


tnx.. you probably saved my dev kit .. made a big mistake and connected the pull ups to 5v rail on the expi board.
somewhere deep back in my head i knew it was wrong.
I even had a look at the I2C signal with my scope .. but no lightbulb flashing yesterday.

tnx again .. :smile:

(Jose Marcelino) #132

Great news Mouser just shipped my RM186s modules!

Now to design a PCB for them...



(Gonzalo Casas) #134

Hi @Charles! I finally received everything to test your boards! The RM186 modules arrived and so did the breakout boards!

Now, stupid question: what is minimum required in your PCB and what is optional? Can I just solder the RM186 to the board, add some headers and plug it to my machine via FTDI already?

Sorry if this question is too noob-ish, I want to try the minimal configuration for the board, and I also want to prevent ruining it because of my ignorance :slight_smile:



Hi @gonzalocasas

Well, really depends on what you want to do, if it's just for doing Serial com with FTDI, you need to double check that your FTDI (or clone) is full 3.3V (power and RX/TX pin) but, real genuine FTDI chip may not have enough power on their on board regulator for powering 3.3V device (it's the case for ESP8266 but may be sufficient for LAIRD, I don't know)

So having a FTDI like this with on board regulator can save your life, trust me they are a must have (and I don't speak about fake FTDI headache), so CH340 or CH341 chipset is really really worry free for FTDI I've got these one or

So if you have one of this adapter and to be sure to works on all situation, I suggest to solder
- the Laird Module
- FTDI header
- C1 and C2
- On board 3.3V regulator MCP1703 (or other eq)
- D1, D2, and D3 (Schottky) 1N5819 or other
- Solder paste on bottom jumper pad from 1-2 TO Reg (use on board regulator) that's all

And with this config, if this is not working due to power supply problem or if you have other FTDI adapter, you can apply external supply (up to 12V), from +/- of the board (lipo entry) or with a lipo.

Then all that is following assumption since I do not have all in my hands yet
may be need
- R1, R2, R5, if you use I2C put R3 and R4
- R7 / R6 just if you want to measure Vbat from code

But this board has not been tested, use at your own risk for now :wink:

may be @BoRRoZ could tell us more

, in this case yo can power the board with 3.3V or put the on board regulator
and have on board regulator says 3.3V, I strongly suggest to put the 3.3V regulator, it could save your module and does not hurt


sofar I've used the onboard UART interface from the dev. kit only
but there is a header so I'll try tomorrow to connect it direct to an usb-serial FTDI cable.

maybe pin nAutoRUN need some attention


@Charles I just noticed the circuit diagram does not seem to contain the decoupling capacitors mentioned by Laird:

@gonzalocasas After soldering the module in place (make sure to connect all ground pins, from the documentation: "All module GND pins MUST be connected to host PCB GND.") I will add two 100nF SMD capacitors at the power pins (two pins at the left and right bottom of the module when the PCB is oriented with the wider part on top) to the ground when populating my board.


Thanks, I missed those one, but I'm pretty sure they are also on the Laird board internal design and laird are just taking precaution. I can't believe they didn't put decoupling caps on power line of the board !

But since GND pin is just near 3V3 pin on laird module it's should be easy to solder one between two pins as @kersing just said. But I really think we can live without them for prototyping.

@BoRRoZ, correct NARun is pulled up with R5 :wink:

(Jose Marcelino) #139

Yes think I see some decoupling inside the can too, should be no problem. Just Laird being extra cautious


They did add the capacitors to the development kit, so I will add them just in case... Someone else may risk not adding them and report back :wink:


hummm, interesting picture, SX1272 not SX1276 ?

How did you removed the case so nicely ?

And today's a great day :wink:

(Nestor Ayuso) #142

maybe in FCC-ID batabase


lol :innocent:


Amazing, was not aware of this, thanks for sharing