RAK3172 Internal Schematic

I wrote custom firmware for the RAK4270 and would like to port it to the RAK3172 but haven’t been able to find an internal schematic.

Are there any documents detailing the RF switch pins, TXCO specs, and any other information about the module that would be useful for writing firmware? With the additional pins and lower price point, it’s a very exciting new module for custom applications!

Hello @mintenj

I am sorry, but we are not releasing the internal schematic of the RAK3172.
About the RF switch and TCXO control I can give you only a snapshot of the connections.

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That’s perfect, thank you for the information on connections!

Would it be possible to also get either the part number or specs for the TXCO. I would like to use the RX duty cycling feature which makes the minimum settling time very important, as well as it’s input voltage range. It’s also helpful to know the accuracy and temperature variance to determine what modulation settings are possible.

I have to check next week. I do not have the BOM of the RAK3172.

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you can check this breakout board I made here

Then associated definition I made for mbed-os but shows pinout

and the radio driver done accordingly here to control the pin

    // Radio specific controls (TX/RX duplexer switch control)
    mbed::DigitalOut _rf_switch_ctrl1(PB_8);
    mbed::DigitalOut _rf_switch_ctrl2(PC_13);

Confirmed to work I had some trouble to connect at the beginning because at 1st start I left TXCO feature enabled.


Impressive work @Charles :100:

Nothing fancy or complicated in the design. Just pure functionality and it is great to hear it works smoothly!

Can we share it via our social media channels so many other people can see it? :slight_smile:


Thank you @carlrowan, but you helped me a lot providing the needed information, thanks :slight_smile:

Sure you can share, of course.


Very nice work! Thank you for sharing!

Any luck with the TCXO datasheet?

Sorry, I do not have got any feedback. It looks like we have several similar TCXO from different suppliers in our BOM because of the current electronic component crisis. => RAKwireless: Update on Components Lead Time

Thank you very much [Charles] !

Oh yikes, the component shortage has definitely required some flexibility. Do you know if any worst case specs or parameters have been defined?

For anybody following this post, it appears a TXCO is not actually placed? It’s disappointing as this limits the LoRa modulation settings that are possible. It’s also disappointing there’s missing documentation (internal schematic) and incorrect documentation (block diagram indicating a TCXO). This does not instill confidence in RAK wireless or this module which is too bad considering it’s excellent price point.

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Hi @mintenj ,

Sorry for the confusion. TCXO was the original plan but the global shortage made us pivot. There are few STM32WL SoC based LoRa modules out there and with RAK3172, it will give another module options for developers. RAK3172 with TCXO is still in the pipeline but sadly it seems not to be fitted on your application. For common LoRaWAN end-device requirements, the RAK3172 will be good or even better with its price point and sleep performance (no need for sleep command because it is always in low-power mode) :+1:

But for custom firmware and LoRa modulation like you need, what we can offer is the RAK4270 which we have now with TCXO in it.

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Is there a timeline for RAK3172 with TCXO? Maybe during next year? I can imagine this was the reason for so low price in this module. I remember it’s original price was 7.2$, instead of 5.99$ like it’s now.

For may project (I will use Lora peer to peer communication) TCXO will be a must. Also I would need more pins that RAK4270 has, so RAK3172 with TCXO would be perfect

Hi @frohike2008 ,Sorry, we don’t have a TCXO version of rak3172 yet. If we launch it, we’ll inform you at the first time. I want to know why TCXO must be used, what conditions or scenarios are there? We look forward to your reply. Thank you very much.

Hi Daniel, in my project I will use maximum output power (22dBm is possible in EU 869.4-869.65MHz Band) with SF11 and longest message can last 1.7 seconds. With this configuration the maximum Freq. drift is 20.3Hz (BW/3*2^SF). Looking at AN1200.37 (Recommendations for Best Performance) document, I can see the drift in the fequency will be too high without using a TCXO

But I see that activating Low Data rate might solve this issue because the the drift error can be 324,8Hz in my configuration

The problem is a longer transmission time with LDRO activated, but we are also saving the power consumption of the TCXO. I don’t know I will need to make testing to be sure that this can work

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OK, thank you very much for explaining, I understand, we are planning TCXO versions, if there is release, I will inform you in time. In addition, how is your test results, is the effect of Low Data Rate?

Hi Daniel, I didn’t want to buy any WisDuo RAK3272S Breakout Board until I was sure I could use it for my project. But knowing this I will give it a try

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