FrSky telemetry mod without RS232 level converter

All mods related to the frsky telemetry series of the firmware
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Kilrah
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FrSky telemetry mod without RS232 level converter

Postby Kilrah » Tue Feb 28, 2012 1:07 pm

We have seen many different versions of the mod for FrSky telemetry (here), but all involve using an RS232 level converter. Some proposed schematics are simpler than others, but of course the simplest is not to use one at all. This obviously involves getting into the module, and tapping the lines between the processor and the level converter on the board.

Two of us have just been doing the mod, one with the DIY module, and me with the JR-style one. My version is based on Mike Blandford's reuse of the 2 unused module pins, but routing the module's TTL level signals to them instead of the RS232 level backside pins.

Here we go for the DJT (click on the images to have them in larger version, apparently the forum shrinks them down for display):

Image
- Cut the trace next to the via below R25 (perform 2 cuts 1mm apart, and lift/remove the bit of copper inbetween)
- Scrape the soldermask off the via and about 2mm of the trace, whis is where the blue (RX) wire will be soldered
- Scrape 2mm of the track above it, a bit further away (no cut!) to solder the black (TX) wire

Image

- Solder a 1k resistor over the cut you did on the RX track. This one will allow updating the module's firmware.
- Solder the blue RX wire to the end of that resistor
- Solder the black wire to the TX trace
- Solder the other end of the wires to the module connector. I added a 47 Ohm resistor in line with the RX line, this wouldn't really be needed but is thought as a protection.

In the radio:

Image

Image

- On the backplane, cut the traces that goes to ground on the 2nd pin. One on the "inside", and 2 on the module side!!
- Connect the 47 Ohm resistor to that pin
- Connect the 2 serial wires to that resistor, and to pin 5. I used a servo plug in order to be able to easily separate both case halves in case I need to do more work.

Finally in the radio, solder the serial wires to the TX-RX pads:

Image

So this allows configuring alarms, receiving and displaying telemetry, reflashing the radio without removing the module, AND reflashing the module without removing it from the radio.
Please note that the radio sends alarm configuration data to the module when powered up, when model is changed, and if alarm settings are changed in the telemetry screens. So in order to avoid conflicts when you want to upgrade the DJT's firmware, just don't start editing telemetry settings or changing models during flashing, and wait a couple of seconds after powering the radio up before pressing "Download" in the Frsky flash utility!

The locations for a DHT can be found here: http://www.rc-cam.com/forum/index.php?/ ... r9x-hacks/
Last edited by Kilrah on Mon May 14, 2012 2:56 pm, edited 5 times in total.

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Re: FrSky telemetry mod without RS232 level converter

Postby cre8tiveleo » Tue Feb 28, 2012 2:15 pm

Nice nice, I just did the module mod for a friend, stuck a lp4dsm in a spare module, antenna inside which works better for him.

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Re: FrSky telemetry mod without RS232 level converter

Postby erazz » Tue Feb 28, 2012 4:26 pm

Nice work!!!

very neat.
The only problem I see its that you lose the ability to update the FW for the tx module... Don't you?
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Re: FrSky telemetry mod without RS232 level converter

Postby erazz » Tue Feb 28, 2012 4:46 pm

Now that I think about it.... It's probably easier and smarter to use the 232 module to flash fw and keep it off the transmitter altogether. Nice!

Would you like to do a wiki page? I think it's highly worthwhile.
Maybe here: http://9xforums.com/wiki/index.php/How_ ... _telemetry
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Re: FrSky telemetry mod without RS232 level converter

Postby Kilrah » Tue Feb 28, 2012 5:59 pm

erazz wrote:The only problem I see its that you lose the ability to update the FW for the tx module... Don't you?

Actually yes, because I've cut the "RX" trace coming from the onboard level converter. But, AFAIK simply bridging that cut with a resistor should allow it again. It's never good having 2 transmitters on the same line, but if each has an inline resistor there should be a point where one can talk with the other connected as long as it shuts up (and the 9X only sends stuff to the module once in a rare while, right?). Now it would take some experimenting to verify that, that I'll very likely do when there's a firmware upgrade available for my module... I don't think I'll mess up with a working system before needed, lead times are long on those things at the moment if I screw up :D

What I know is that I'll likely buy a second 9x and module set pretty soon as a backup, trainer setup, you name it - and who knows, maybe sell my Futaba T14, I don't think it offers me anything I need the 9X can't anymore... it's more like the opposite, and the 9x is actually more convenient in most ways, and once we have PXX and 16 channels - no comment!! :shock:

I'll see about doing a Wiki page one of these days indeed, might be worth it. The trainer port stuff as well for those who fly FPV.

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Re: FrSky telemetry mod without RS232 level converter

Postby Kilrah » Mon May 14, 2012 12:08 pm

Kilrah wrote:
erazz wrote:The only problem I see its that you lose the ability to update the FW for the tx module... Don't you?

Actually yes, because I've cut the "RX" trace coming from the onboard level converter. But, AFAIK simply bridging that cut with a resistor should allow it again.

OK, now that I have received and modded my 2nd DJT, I've done the test and confirmed it works perfectly fine.

The first post has been updated with more details!

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Re: FrSky telemetry mod without RS232 level converter

Postby Clivew » Wed Jun 06, 2012 8:39 pm

Has anyone else done this mod, if so did your alarm beeper work?
(PiSkpkr works fine on er9x if you have a speaker fitted)
Mine doesn't and I can't seem to find out why :?

Clive

P.S. Switched it on tonight, and it's working perfectly! Don't know what
that was all about, maybe the bleeper itself was stuck..perhaps. :roll:

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Re: FrSky telemetry mod without RS232 level converter

Postby Clivew » Sun Jun 10, 2012 12:13 am

And it continues to work perfectly :)
I wonder if ersky9x board is happy with this modification to the module?
I'm guessing not and I have to not swap modules between the two??
Just a thought, as I have an ersky transmitter here also.
Thanks,
Clive

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Re: FrSky telemetry mod without RS232 level converter

Postby Kilrah » Sun Jun 10, 2012 5:55 am

Hmm I'm afraid not, because the ersky9x board was designed to avoid the external converter and has it on the board, and thus expects direct connection of an unmodified module.

If someone from the development team made a software option to read telemetry data from UART3 (the port intended for the Bluetooth module) you could however connect your modified module there as it works on 3.3V as needed.

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Re: FrSky telemetry mod without RS232 level converter

Postby skelator » Wed Jun 13, 2012 5:56 am

thank for the mod but I don't have smd resistor i guess i can still use normal resistor just a bit bulky
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Re: FrSky telemetry mod without RS232 level converter

Postby Kilrah » Wed Jun 13, 2012 6:10 am

Of course.

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Re: FrSky telemetry mod without RS232 level converter

Postby skelator » Wed Jun 13, 2012 10:30 am

great thanks
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Re: FrSky telemetry mod without RS232 level converter

Postby defyboy » Sun Jun 17, 2012 4:25 am

This is awesome, On my to-do list once I get my gear. Thanks.

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Re: FrSky telemetry mod without RS232 level converter

Postby skelator » Mon Jun 25, 2012 11:15 am

sorry the 470ohm is use for protection when upgrading the DJT modules? I have none at the moment I can live w/o the 470ohm ?
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Re: FrSky telemetry mod without RS232 level converter

Postby Kilrah » Mon Jun 25, 2012 7:43 pm

There are 2, and at least one (the one shown on the back PCB) is needed, otherwise you'd have to remove the module everytime you flash the radio. The one in the module could be omitted.

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Re: FrSky telemetry mod without RS232 level converter

Postby mbanzi » Mon Jul 02, 2012 3:20 pm

Kilrah, how did you get the circuit board out of the module case? It seems it would be a little easier to do the mod with the board removed, but mine seems to be glued in there!

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Re: FrSky telemetry mod without RS232 level converter

Postby Rober7 » Thu Jul 12, 2012 8:58 am

Hello there!

@ Kilrah, this is a very nice mod you made there!
Thank you so much! I've completed phase 1 and 2 and am currently working on modding the transmitter side when i came along something weird:

frsky03question.jpg


do i need to cut the trace below the 1k resistor?
the 1k resistor isn't mentioned in your post, do i need it at all?

thanks!

EDIT: got it already, without cutting the line the resistor would be useless. Unfortunately i bricked my Atmel while flashing :( have to find a new one untill i can test the mod..


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Re: FrSky telemetry mod without RS232 level converter

Postby jhsa » Thu Jul 12, 2012 5:42 pm

go to the wiki.. some people bricked their chips and brought them back to life.. there are tutorials about it
My er9x/Ersky9x/eepskye Video Tutorials
https://www.youtube.com/playlist?list=PL5uJhoD7sAKidZmkhMpYpp_qcuIqJXhb9

Donate to Er9x/Ersky9x:
https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=YHX43JR3J7XGW

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Re: FrSky telemetry mod without RS232 level converter

Postby Kilrah » Thu Jul 12, 2012 10:12 pm

I didn't mention the 1k resistor because it's now an "obsolete" mod. Don't do it.
It was to solve a problem when using the trainer port in "student" mode, but we now have an option in the firmware instead.

mbanzi wrote:Kilrah, how did you get the circuit board out of the module case? It seems it would be a little easier to do the mod with the board removed, but mine seems to be glued in there!


Had missed that one. Probably too late, but yes there are "hooks" on the sides of the plastic case that hold the module down. Warp the module case a bit while pulling on the switch PCB and it will pop out.

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Re: FrSky telemetry mod without RS232 level converter

Postby Spoogy » Tue Jul 17, 2012 1:21 pm

I'm just about to starting to make this modification also. I tried once already with RS232 but it didn't succee. :roll:

I triple read the first post and gathered all the needed parts. I see that those two 220 Ohm resistors are needed for atmega even that they are not mentioned in first post?

Another one what I'm wondering is that there's two 470 Ohm resistors. One inside of module (just for additional protection) and another one connected to that 2nd pin on back circuit. BUT as far as I can see these resistors has YELLOW, PURPLE and BLACK stripes. Isn't that 47 Ohms then because there is only 4 bands/stripes on that resistor? 470 Ohm would be yellow, purple and brown with the 4 bands. With 5 band those resistors in picture would be 470 Ohm.

can someone clarify/confirm that or do I not understand something here (again :roll: )? I will hold on until someone can confirm that.

edit1: Ouh, and third question / confirmation. In another frsky mods with level convertor there is a trace cut on radio back board at the pin 5. So both 2nd and 5th pins are isolated. In this modification I see that it's unneccessary. Am I right?

edit2: resistor color codings -> http://www.michaels-electronics-lessons ... -code.html

edit3: I have now undone my previous modifications inside of frsky transmitter module and soldered those two wires onto the traces with that 1K resistor. Now I'm waiting for confirmation for that 470 Ohm reisistor. Is it so or is it 47 Ohm?

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Re: FrSky telemetry mod without RS232 level converter

Postby Spoogy » Tue Jul 17, 2012 5:23 pm

Because nobody hasn't aswered (yet) I decided to continue by using 470 Ohm resistor as indicated at the text. This is how it looks like now.


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Re: FrSky telemetry mod without RS232 level converter

Postby Spoogy » Tue Jul 17, 2012 9:57 pm

And continued the mod. Now all wiring inside of radio processor board has been done. I'm using JST connector to separate back from the front and now I have only to solder that resistor and jst connector to backboard and its ready. Everything seems to be good at least what I have measured. Firmware need to be updated after this....

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Re: FrSky telemetry mod without RS232 level converter

Postby Kilrah » Thu Jul 19, 2012 12:49 pm

Yup indeed, looks like I've use 47 Ohm resistors by mistake on my equipment...

It shouldn't matter much though. I took the 470 Ohm from the existing mod documents, apparently chose the wrong resistors, and well, it works perfectly, so... :D

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Re: FrSky telemetry mod without RS232 level converter

Postby IceWind » Fri Oct 26, 2012 1:07 am

Hey,
I did this mod and so far receiving telemetry is working fine.
But sending commands doesn't seem to work. The 9X can't read the RSSI alarm levels and neither I can if I use the
module back pins.
I've checked all connections and seem all fine. Measured 1470R from the exit connection of the RX line in the module to the other side of the 1K resistor.
Any idea what it might be, I was disable the 1K resistor to try but as I've used a small SMD it would be tricky and I wanted to avoid it. :)

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Re: FrSky telemetry mod without RS232 level converter

Postby Kilrah » Fri Oct 26, 2012 7:09 am

Are you sure the wire and the end of the smd resistor that are supposed to contact the track really do so? BTW I used a 47Ohm resistor, not 470 as Spoogy found out, it was a typing mistake. I corrected the first post, but you might have seen it earlier. 470/1k might indeed not cut it. If using 470Ohm, you might want to use a 10k instead of 1k.

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Re: FrSky telemetry mod without RS232 level converter

Postby Spoogy » Fri Oct 26, 2012 2:36 pm

I have that 470 Ohm resistor inline with 1K resistor in my module and I can confirm that it works (as far as I understand telemetry).

I can see the Tx and Rx levels in telemetry view and they will change if I hide antenna from either end of (RX or TX antenna) with my hand.

Also I can see supply voltage from receiver via A1. Or is there something that I don't understand now??
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Re: FrSky telemetry mod without RS232 level converter

Postby Kilrah » Fri Oct 26, 2012 2:57 pm

That connection with the cut trace is the one going FROM the radio TO the module, and is used to set the alarm levels on the frsky module itself. The telemetry data FROM the module TO the radio travels through the other connection.

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Re: FrSky telemetry mod without RS232 level converter

Postby IceWind » Fri Oct 26, 2012 4:08 pm

Yeah exactly and I can get Telemetry data without issues.
It's just when "requesting" the alarms values that it doesn't work.

"BTW I used a 47Ohm resistor, not 470 as Spoogy found out,"
I believe you meant to to say "not a 47ohm".
So yes I'm using a 470 ohm resistor there, that makes the reading 1470ohm: 1K (100ohm) + 470ohm

I took care to test by measuring from the other side of the resistor (opposed to the side where the wire goes). But yeah the
problem could be right on that solder joint. Today I'll try and measure it into right into the pin of the uC itself up to the module connector.

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Re: FrSky telemetry mod without RS232 level converter

Postby Kilrah » Fri Oct 26, 2012 4:34 pm

No, I meant "I used 47 ohms, not 470 ohms".

Seems the 0 and the O look a tad too similar :D

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Re: FrSky telemetry mod without RS232 level converter

Postby IceWind » Fri Oct 26, 2012 4:56 pm

Ehehe! :)
It's better to use the R notation. So you've used a 47R resistor. :)

I'll try to change it today to a SMD 10K (if I don't find any 47R at home) and see how it goes.


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