frsky telemetry on turnigy 9x without rs232/transistor/flying cables/holes - Page 3 - RC Groups
Thread Tools
Apr 07, 2012, 11:42 AM
Registered User

Thanks Zen09

Could you detail exactly how many and where the 100k resistors get installed? Thanks again for the simplicity of this mod.
Sign up now
to remove ads between posts
Apr 07, 2012, 12:16 PM
Registered User

Zen09 - One More Question

2. It is not a coincidence, it's OK since 2 pots/switches have been rerouted to the upper ADC's on the Atmega (they were on MOSI/MISO and would have made the communication with the module impossible).[/QUOTE]

I thought that only the Ail and Thr switches were affected (rerouted). Are you saying that the P3 pot is also affected?

Apr 07, 2012, 01:33 PM
Registered User
Zen09's Avatar
2 resistors inline with the MOSI / MISO channels that go to the frsky module.

OK, I've checked right now, it's the AIL and THR, so I don't know where your problem could come from.
Apr 07, 2012, 10:15 PM
Registered User

Zen09 - 100k resistors

The 100k resistors worked great....Any other tips please pass along.

Thanks Earl
Apr 08, 2012, 05:23 PM
Registered User

Zen09 - Problem

After setting A1 alarm with the 100k resistors mod. installed I do not get audible alarm (low voltage) via the DHT.

Apr 09, 2012, 03:25 PM
Registered User
Zen09's Avatar
You're right, I didn't notice this.

I looked on the screen, saw the telemetry data and thought everything is okay. Rssi alarm doesn't work either so it turns out to be okay only from module to 9x and not from 9x to module.

I guess a lower value resistor will solve the issue. I'll investigate when I have time.
Apr 11, 2012, 09:56 AM
Registered User
Zen09's Avatar


A 15ohm resistor will do. It is required only on MISO, you can leave MOSI with no resistor.

I was surprised by how low the resistance should be for the signal to pass. I can't tell the tolerance interval, except that it must be less than 200
Try whatever works and reply back so I can update the video.


No resistor needed! I've figured out the clicking noise is caused by the interference with the max232 chip, which should be disconnected, as shown below.

The image shows the DIY DHT layout of course.

After you disconnect the chip you won't be able to use the external TXd/RXd of the module, but why would you want that? Since everything can now be programmed from the 9x, the only reason would be to change module firmware using a ftdi interface.
But you would do this first (if you want rom B fw. that enables you to set failsafe from TX) then no more need to do it again.
Last edited by Zen09; Jan 25, 2014 at 12:19 PM. Reason: update on the issue
Apr 21, 2012, 04:52 PM
Registered User
Zen09's Avatar
I have been asked on YT to give some details about the serial communications on the DHT module so here they are.

This is the STM32 datasheet (page 30, second column, pins 30-31 are marked as USART1_TX/RX)

As I marked in the photo, pins 30-31 are connected (through some traces on another PCB layer, not visible) to pins 11-12 of the MAX323 TTL converter.
Pins 13-14 (converted signal from the MAX chip) are connected to the external TX/RX of the FrSky module (blue marked traces).

So why would someone use a TTL converter to convert the signal back from the external tx/rx (already converted), when it is more straightforward to directly connect to the original tx/rx from the module brain.
Apr 21, 2012, 08:05 PM
RC beginner
Originally Posted by Zen09
So why would someone use a TTL converter to convert the signal back from the external tx/rx (already converted), when it is more straightforward to directly connect to the original tx/rx from the module brain.
lack of understanding on how asych serial interfaces really work. specially true among software engineers but even some experienced hardware designers. there was a time when non-inverted rs232 (idle low) was the rage. ibm pc inherited this polarity from teletypes, minicomputer terminals, etc.. then with the advent of hardware uarts and microcontroller chips 5v inverted (idle high) reared its ugly head and all hell broke loose.

now with incompetent terms like "ttl serial" being tossed around things get even worse. the biggest tragedy is uP designers never quite appreciated the need for polarity control on their uarts (xor gate costing fraction of a cent). so there is huge waste and un-necessary expense on devices like max232.

bottom line: "level" is irrelevant but polarity is critical. few understand this even today.
May 06, 2012, 06:39 AM
Registered User
Hey Guys,

f the connection with the pcb is cut. Would you still be able to use the old turnigy 9x module ?

May 06, 2012, 07:42 AM
Registered User
Zen09's Avatar
Not sure what you mean.. Why wouldn't you still be able to use the old module?
May 07, 2012, 12:00 PM
Registered User
Originally Posted by RENATOA
I'll try to explain the first two pictures.
His choice was to use the two unused module pins, that in original JR module are used for 6V and former FM antenna, to route the serial line between Frsky module and 9X.
Inside Frsky module these pins are free, I already used them in other project to pass two signals.
In the first picture the thin wires connects these two pins to the Frsky serial line, before the MAX circuit, so to TTL levels, as needed by 9X. This way we have the Frsky serial lines, with good TTL levels available at module pins, and no more external wires / case hole are needed. And also no more need for transistors inside 9X.
But inside 9X these pins are connected to PCB. To make them usable for this purpose, he cut around them in the second picture, making the pads available to transport the serial line from Frsky module inside 9X.
Sorry I'm referring to how emerge cut around the PCB in the second picture. With this done, if i try to use any other tx module i.e old turnigy 9x, wouldn't the cut not make it work?
May 07, 2012, 12:20 PM
Registered User
There are two pins in discussion:
- one is antenna, I mean the older telescopic FM antenna. If you cut this pin, you still can use any 2,4G module, but no an old FM module.
- the other pin is a 6V pin, used by original JR modules only, no other brand adopting this case use it, as far as I know.
May 10, 2012, 04:52 AM
Registered User
Hey guys, I made a blog post where I try to clearly explain what you need to do to your 9X to get it to support the FrSky telemetry:

Any suggestions what I could add or be more clear about?
May 10, 2012, 05:35 AM
Registered User
Zen09's Avatar
Beware, your MOSI connection to 9x seems wrong to me! It is not clear from the picture..

Perhaps you should use my picture

And this one for the USBasp interface
Last edited by Zen09; May 10, 2012 at 05:40 AM.

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Build Log Turnigy 9X and FrSky with Telemetry for Dummies Art Newland Radios 28 Sep 11, 2016 12:29 PM
Question Sell my DX6i for 9x w/frsky telemetry? razorseal Radios 12 Oct 18, 2011 11:08 AM
Discussion Sell my DX6i for 9x w/frsky telemetry? razorseal Radios 8 Sep 15, 2011 06:55 PM
Question Is there a firmware that supports Frsky telemetry for 9x? razorseal Radios 0 Sep 15, 2011 12:07 AM