er9x and multi-protocol telemetry mod

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er9x and multi-protocol telemetry mod

Post by Timeless » Mon Aug 10, 2020 1:56 pm

Hi All,

I've been a happy user of er9x(M64) in combination with a multi-protocol for quite some time now (thanks developers), and thus it seems the appropriate time to do the MPM telemetry mod to receive the (AFHDS 2A) RSSI readings.

But there does not seem any exact documentation on how to install the MPM telemetry mod.
I've read that PIN2 of the Atmega (also known as MOSI) should be connected to PIN5 (also known as RF out/Unused) of the module bay (presumably through a 470ohm resistor).
but that's about it.

So my questions are:
1. Atmega PIN2 (MOSI) -> Module Bay PIN5 (RF out/Unused)?
2. What value should the series resistor have? 470ohm?
3. Is it required to cut the trace of PIN5 in the module bay? (as shown in Oscar Liang's FrSky blogpost)
4. Is it still required to rewire the switches to PIN41/PIN42? (like with the FrSky telemetry mod)
5. Are there any pictures of this MPM telemetry mod?
6. Is the er9xProv822t.zip -> er9x.hex file prepared to receive AFHDS 2A telemetry?

Regards,
Timeless


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Re: er9x and multi-protocol telemetry mod

Post by amxcs » Tue Aug 11, 2020 6:01 am

+1 for the same question

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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Tue Aug 11, 2020 9:02 am

In order to use the serial pin on the ATMEGA, you need to do the telemetry mod that involves moving the THR and AIL switches to different pins of the processor.
1. Correct.
2. 470 ohms is good.
3. Not needed.
4. Yes.
5. Go here: https://github.com/MikeBland/mbtx, and look in the section "FrSky Telemetry Mods", there are several descriptions, with pictures, of the telemetry mod. If the Multi module is flashed with firmware that doesn't sent inverted telemetry, then you don't need the inverter/buffer, just connect using the 470 ohm resistor.
6. Yes, but I still need to add processing for "extended telemetry" items sent using AFHDS2A.

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Tue Aug 11, 2020 10:15 am

Thanks for the explanation Mike :).
Now I know that the telemetry mod of the MPM and FrSky are almost identical.
Which means the pictures are also valid for the MPM telemetry mod.

May I ask how the Atmega communicates with the MPM afther the mod?
Because only (Atmega)PIN2 RX is connected to (MPM)PIN5 TX, but (Atmega) PIN3 TX is left unconnected?
That probably means ER9X communicates to the MPM module over the PPM pin of the module bay, and responses from the MPM are recieved over PIN2?

If my assumptions are correct moving PIN3 to PIN42 is not actually required for the MPM telemetry mod, but is needed so the firmware can handle both situations identically?
MikeB wrote:
Tue Aug 11, 2020 9:02 am
6. Yes, but I still need to add processing for "extended telemetry" items sent using AFHDS2A.
But RSSI is already supported right?
And even if it isn't, I can validate if I did everything correct when I see the MPM version number in de protocol screen I suppose.

And my radio has the M64 processor, doesn't that mean I need er9x-frsky.hex? To tell the radio I did the frsky telemetry mod?

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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Tue Aug 11, 2020 10:30 am

Timeless wrote:
Tue Aug 11, 2020 10:15 am
Because only (Atmega)PIN2 RX is connected to (MPM)PIN5 TX, but (Atmega) PIN3 TX is left unconnected?
That probably means ER9X communicates to the MPM module over the PPM pin of the module bay, and responses from the MPM are recieved over PIN2?
Yes
Timeless wrote:
Tue Aug 11, 2020 10:15 am
If my assumptions are correct moving PIN3 to PIN42 is not actually required for the MPM telemetry mod, but is needed so the firmware can handle both situations identically?
Yes
Timeless wrote:
Tue Aug 11, 2020 10:15 am
But RSSI is already supported right?
And even if it isn't, I can validate if I did everything correct when I see the MPM version number in de protocol screen I suppose.
Yes, RSSI and standard telemetry is OK, just extended telemetry is not in.
Timeless wrote:
Tue Aug 11, 2020 10:15 am
And my radio has the M64 processor, doesn't that mean I need er9x-frsky.hex? To tell the radio I did the frsky telemetry mod?
Yes

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Tue Aug 11, 2020 10:54 pm

I've done the telemetry mod
Flashed er9x-frsky.hex and multi-stm-opentx-aetr-noinv-v1.3.1.49.bin to the transmitter and MPM.
(I've read somewhere that the opentx version is recommended and can be used with er9x?)
when I browse the protocol menu it does jitter a bit at first (incomplete version number/protocol), but after 2 a 3seconds it's steady and shows the firmware version and protocol name.

However I tried a Flysky FS-X6B receiver (which should be telemetry enabled) but it shows some odd RSSI values.
The TSSI is mostly at 0, but every so often (mostly random +/-5sec interval) it shows a value, and the RSSI seems quite high to me.
When I made the pictures I had the TX and RX close to each other (<1meter), but the RSSI does drop when I put them 25m apart (RSSI around 185).
20200811_231358(0).jpg
High RSSI, with TSSI
20200811_231401.jpg
High RSSI, without TSSI

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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Wed Aug 12, 2020 11:30 am

I should be able to build a special test version to look into this. I don't have any AFHDS2A receivers so I can't test it myself.
Please confirm you don't have a voice module and are flashing er9x-frsky.hex.

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Wed Aug 12, 2020 11:49 am

Yes only the FrSky mod is installed. And flashed er9x-frsky.hex.

EDIT
I've seen this post where someone does say that RSSI values work.

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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Wed Aug 12, 2020 2:03 pm

It's quite possible that the telemetry signal from the module is not driving to a high enough voltage. The '64 needs to see at least 3.0V, while the module output is a pullup to 3.3V with a diode in series. This could be causing data errors (possibly causing the jitter in the protocol menu).

Things to try:
1. Reduce the value of the 470 ohm resistor, you could try with 0 ohms (direct connection).
2. Add a pullup resistor to pin 2 of the '64 (e.g. 4K7).

I could enable the internal pullup on pin 2, but this is only 20K to 50K, but it may be enough.

I have problems on my 9X that has a '2561 processor and a RS232 buffer on the input. The STM module doesn't drive the input high enough, I have to test using an AVR module (that outputs a 5V signal).

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Wed Aug 12, 2020 2:23 pm

Ok I will try a direct connection.
But the resistor is to limit the current, is the current into the Atmega really that high that the voltage drops?

And the RSSI is always visible, and drops evenly when I walk away from the receiver while holding the transmitter. If there is jitter on the line shouldn't that number also be all over the place? Only the TSSI frequently disappears.

From what I understand RSSI is communicated from the reciever to the transmitter right? And TSSI is then measured by the transmitter? Because to me it almost seems like the receiver does periodically send its RSSI and only then the transmitter is able to measure the TSSI.

The diode is in series with the RX pin of the STM, so 5v tolerance is achieved? Otherwise a pull-up to 5v might destroy the STM.

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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Wed Aug 12, 2020 3:42 pm

The TSSI is a single byte in the data, the RSSI is a telemetry value so that there needs to be a correct ID field as well as the data.

If data is being lost/corrupted, then whole packets will be ignored.

The telemetry signal is buffered by an XOR gate device and is 5V safe due to the diode and the pullup you may add limits current in any case. The STM processor actually has 5V tolerant I/O pins.

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Wed Aug 12, 2020 3:51 pm

But what does TSSI mean? Is it the Transmitter's RSSI for telemetry messages?

Funny that almost all STM flashing tutorials mention not to put the serial adapter on 5V even when not providing power the the STM.

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Wed Aug 12, 2020 9:57 pm

I've changed the 470ohm resistor to a 100ohm so I have at least some ESD protection on the module bay.
The protocol screen is now stable, fast and no jitter. (have to say I only saw it jitter once or twice with the 470ohm resistor)
However the RSSI and TSSI didn't change, still way above 100 and infrequent updates.
I also tried another receiver (that's in my Eachine E010S Pro) and that one only updated its RSSI once ever minute and only from a close range.

Here are some pictures of my soldering and wiring.
(I reused the 200ohm SMD resistors to make it a little neater).
complete wireing.jpg
Entire overview.
remapped_pins_41_and_42_part1.jpg
Pins 41 and 41 at Atmega.
remapped_pins_41_and_42_part2.jpg
Pins 41 and 41 at source.
pin2_to_pin5_interconnect.jpg
Dupont interconnect, so the case can still be separated.

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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Wed Aug 12, 2020 10:52 pm

I'm working on a test version of firmware that should provide some debug data, I should have it ready tomorrow.

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Thu Aug 13, 2020 7:06 am

Thanks Mike, I'm waiting patiently. No need to rush ;).

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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Thu Aug 13, 2020 9:32 pm

Just posted a test version ("er9x-frsky-AFHdebug"). I've replaced the statistics screen with debug data (UP LONG from the main screen).
Lines 3 and 4 contain the first 20 bytes of a telemetry packet (last byte is on line 5!). To make this readable, they are only loaded (with the next received packet) when you press the MENU button.
Line 6 has 2 values, the first is the number of telemetry packets received and the second is the number of bytes in the last packet loaded above.
Line 8 has 2 values, the first is the number of telemetry bytes received and the second is the number of telemetry bytes that have an error (framing, overrun or parity). Ideally this last value should be 0.

Please try this and let me now what values you get.

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Fri Aug 14, 2020 7:52 pm

I've tested the debug firmware and pressed 'menu' repeatedly (because of irregular RSSI updates) but no telemetry packets appeared.
The counter does increase very rapidly but luckily the bad packet counter stays relatively low. I did see the protocol menu jitter again tho.
debug_screen.jpg
Seems like the MPM is not sending any telemetry packets?
I flashed this build of the MPM firmware
firmware.PNG
(I also tried erSkyTX, but it failed to receive the version number in protocol menu):

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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Fri Aug 14, 2020 10:34 pm

I'll have another look at the code and debug tomorrow (I'll add to the debug), something is being received!
What radio do you have erskyTx on? Since you are using non-inverted serial, you will need to select invert COM1 in the telemetry menu.

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Fri Aug 14, 2020 10:46 pm

MikeB wrote:
Fri Aug 14, 2020 10:34 pm
I'll have another look at the code and debug tomorrow (I'll add to the debug)
Thanks :)
One question about flashing, I noticed that I have to unplug the back (side with battery) from the mainboard in order to flash the M64.
Any idea why that could be? the USBasp is unable to detect the M64 with the back connected.
Not that it's any trouble, but it might cause unnecessary wear on the connectors.
MikeB wrote:
Fri Aug 14, 2020 10:34 pm
something is being received!
Yeah, almost there :)
MikeB wrote:
Fri Aug 14, 2020 10:34 pm
What radio do you have erskyTx on?
Sorry, I meant that I tried the multi-stm-erskytx-aetr-noinv-v1.3.1.49.bin on my MPM as well, to see if that made any difference.
But with that firmware on my MPM, ER9X wasn't able to receive anything at all.

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Re: er9x and multi-protocol telemetry mod

Post by nvd07 » Sat Aug 15, 2020 9:19 am

Hi guys ( new to the forum - discovering er9X after 20 years being mostly out of R/C - great stuff, much more powerful compared to my old multiplex 3010 - congratulations to Mike and all the team. )

I do not mean to hijack this thread but I have somehow related issues , except I did the inverting mod...
I suspect there is something about the levels of the STM32 multimodule as mentionned earlier - unless at this stage you have already ruled out this root cause ?

I did the inverter mod the cheap way with a transistor ( can't remember, PNP I believe, I will look it up and the resistor values too ). It did this to run a stock FRSKY XJT module. works great and I get telemetry, altitude with FRSKY receivers.

Then later on I bought a 4in1 module ( STM 32 - Ytech ) to use with other brand receivers. I was able to bind the 4in1 to FRSKY receivers, FLskyAFDHSS receivers, Spektrum DSMX, however I never was able to get displays of SWR/RSSI/module version...
So I cannot retire my XJT module yet.

So if the 4in1 STM32 output levels are a bit low, it may be possible that the resistor I put in series with the base of the transistor is OK for the XJT module levels but too high for the levels of the 4in1 STM32. I plan to investigate both scenarios with an oscilloscope next week. Maybe I could half this resistor value ...

To give you the full picture, this is with TGY 9X - m64 - inverted mod (transistor) - running : er9x-frsky.hex pro v822s
4in1 module - STM 32 running : multi-stm-opentx-reta-inv-v1.3.1.49.bin ( precompiled . I believe MULTI_TELEMETRY comes pre-compiled in it )
EDIT: i did get mixed up once more between RETA and AETR. this is now multi-stm-opentx-aetr-inv-v1.3.1.49.bin

( at some point I got lost between all the mods and FW configs but I believe I have it correct this time. )


Last thing : about the recent comment from Mike "Since you are using non-inverted serial, you will need to select invert COM1 in the telemetry menu."
I looked for this, to check the opposite as I have the inverting hardware in the Tx and the inverting FW flashed into the module. But i do not see this "invert COM1" in any menu - I believe it is because of the m64 restrictions, am I correct ?

Note later on if needed to help with AFHDS2A telemetry investigation I could do some testing with a TGY iA8 AFHDS2A receiver or a newly acquired (used) FLSKY FS-R9B AFHDS(?) receiver. I picked it up second hand with a near new FLSKY TH9X that has a m128, better than my current m64; but I have not modded this Tx it yet - depending on the outcome of this thread I will mod it one way or the other (inverting or non inverting) to get good telemetry with the 4in1 STM32...

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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Sat Aug 15, 2020 4:55 pm

I've just posted an updated test version, please try the DEBUG screen again. I've moved where the debug is set to try to see what is being received.

nvd07: The XJT actively drives the signal both high and low, the STM multi module relies on a pull up resistor and a diode pulling the signal low.
If you have used a PNP transistor, this may well not work with the STM multi module, you really need to use a NPN transistor.

"Invert COM1" is only present in erskyTx, the firmware for ARM processor based radios.

You could also try the test version I've just posted to see what, if anything is being received from the multi module.

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Sun Aug 16, 2020 3:43 pm

@MikeB: I've tested the 2nd debug build and it does display hexadecimal data now :).
I uploaded a small 3min video to OneDrive, hope this is sufficient?
Image

@nvd07: Welcome ;), hope you can assist us on this AFHDS2A issue once you fix the inverter circuitry.

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Re: er9x and multi-protocol telemetry mod

Post by nvd07 » Sun Aug 16, 2020 7:03 pm

@Timeless thanks for the welcome

@MikeB thanks for the explanations; i looked into my inverting circuit: actually it is NPN , not the PNP i was remembering in my previous post ( i must have made 4-5 different boards to connect various stuff to the frsky module ).
It is a 2N2222, with a 10k resistor between its base and the module bay pin.

Next, i flashed the debug1 firmware. But I guess because the module is not showing up at all in the protocol menu, it means the data transfer from the MPM to the m64 is not working well. In the debug screen I see the telemetry packets counter rising but lots of erroneous packets. There is zero zero in the telemetry lines ( but i had not turned on any receiver - need to transfer back the models into memory first ).

If needed for the investigation i could look at the signal out of my inverting circuit when working with this MPM module (looking for squareness and voltage level).
IMG_20200816_202947.jpg
IMG_20200816_202921.jpg

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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Sun Aug 16, 2020 7:59 pm

nvd07: I suggest changing the 10K to 4K7, and also adding a 10K resistor between the transistor base and ground. Bipolar transistors have a parasitic capacitance between base and ground that needs to be discharged when turning them off. If the driving resistance is too large, then this takes too long and the transistor may not turn off before it is turned back on, or turn off for too short a time. The multi module sends data at 100K baud, the XJT at 57.6K baud.

Timeless: Your video shows the telemetry data is being sent in FrSky Hub format, not AFHDS2A format. Also things like the RSSI value are not being scaled to match the normal, FrSky range.
Also, it looks like a hub telemetry packet is not being sent very often.
Are you able to build your own (custom) version of the multi-protocol firmware?

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Sun Aug 16, 2020 8:27 pm

MikeB wrote:
Sun Aug 16, 2020 7:59 pm
the telemetry data is being sent in FrSky Hub format, not AFHDS2A format.
Also things like the RSSI value are not being scaled to match the normal, FrSky range.
Is that because OpenTX had some issues in the beginning with RSSI and AFHDS2A, like discussed here?
MikeB wrote:
Sun Aug 16, 2020 7:59 pm
Also, it looks like a hub telemetry packet is not being sent very often.
Yeah seems like it, we can almost certainly say that this is caused by the MPM firmware right?
And not because of the 3.3v/5v logic levels both devices operate at.
MikeB wrote:
Sun Aug 16, 2020 7:59 pm
Are you able to build your own (custom) version of the multi-protocol firmware?
Never done it, but I'm sure I can work it out.
What do I need to change?

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Re: er9x and multi-protocol telemetry mod

Post by nvd07 » Sun Aug 16, 2020 8:57 pm

Ok I will modify my 10k resistor to 4k7 and add the 10k to ground. As often with this kind of circuitry, the devil is in the details and it is always interesting to learn about the add-ons needed to cope with the non-perfect operation of the actual components.
Now, while I will be at it with the soldering iron in this area, Mike do you recommend I also add the diode in parallel to the 10k-to-ground, as in Phil's DJT schematic below from your github page ? I would think the diode is not needed here, especially as the XJT is not really sending the true RS232 negative voltages... But I am a mechanical engineer , so I am curious to hear what you have to say about this diode ...
Phils_schematics_DJT.png

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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Mon Aug 17, 2020 12:06 pm

nvd07: The diode is not really needed. The XJT doesn't send any negative voltage. The 2N2222 has a base-emitter breakdown voltage of 6V minimum, so with a 4K7 in series and a 10K to ground, the circuit will be safe to around -9V input. Even then the transistor B-E junction just turns into a zener diode and the 4K7 limits the current.

Timeless: In the protocol menu, change the "Option" value to a negative number (try -128). This will probably show a "Rate 50". This also shows when the value is 0!
I'm not sure what Rate setting is best, but using a negative value should cause the multi-module to send AFHDS2A telemetry instead of FrSky HUB protocol. I asked about this on the RCGroups thread on the module.

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Re: er9x and multi-protocol telemetry mod

Post by nvd07 » Mon Aug 17, 2020 6:31 pm

So i looked into the inverting circuitry today.

Quick look with a scope, ch2 blue at the top is what comes out of the STM32 MPM module , and ch3 pink at the bottom is what my inverting circuit was sending to the TGY 9X M64.

First , before modding anything,
IMG_20200817_175539_10k_feed_before_mod.jpg
It did not look bad from far away; if anything, what I noticed was the overshoots of the STM32.


Then I zoomed in and could see that the rising and falling edges of my circuitry were not quite vertical.
IMG_20200817_175815_10k_feed_before_mod.jpg
IMG_20200817_175755_10k_feed_before_mod.jpg

So i replaced the existing 10k feeding resistor, by a 5k1 I could find, as the box for the 4k7s was empty.
Next I added the 10k to the ground for discharging the parasitic cap. No diode.

Here is the result on the scope, noticeably more vertical, especially on the rising edge:
IMG_20200817_181706_after_mod_5k1_feed_10k_disch.jpg
IMG_20200817_181726after_mod_5k1_feed_10k_disch.jpg


Then I went into the debug menu, and still lots of erroneous packets there. I did bind the MPM to a FrSky receiver this time, GRX8 with vario and altimeter, unlike in my previous posts.
IMG_20200817_193401_after_mod_5k1_feed_10k_disch.jpg
IMG_20200817_193826_after_mod_5k1_feed_10k_disch.jpg
IMG_20200817_193844_after_mod_5k1_feed_10k_disch.jpg
I am puzzled, starting to think my hardware is OK but I must be doing something wrong with the firmwares or the menu settings. :? :? :?

Below is a pic of my 4in1 STM32 MPM module too, as i had not given much details about it so far.
IMG_20200817_202630.jpg

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Re: er9x and multi-protocol telemetry mod

Post by Timeless » Mon Aug 17, 2020 7:10 pm

MikeB wrote:
Mon Aug 17, 2020 12:06 pm
Timeless: In the protocol menu, change the "Option" value to a negative number (try -128).
Great! it indeed works now.
(couldn't find -128, any option only goes as low as -127)
Decent telemetry refresh rate and normal RSSI value, when I put it on anything else than rateX.
Doesn't matter if it is negative/positive, as long as it is not on the rate setting.
Here are some pictures of the telemetry working, but only TSSI (Transmitter RSSI of received telemetry I guess?) seems off.
telemetry_screen.jpg
MikeB wrote:
Mon Aug 17, 2020 12:06 pm
I'm not sure what Rate setting is best, but using a negative value should cause the multi-module to send AFHDS2A telemetry instead of FrSky HUB protocol.
I asked about this on the RCGroups thread on the module.
Yeah I found your post, and I was hoping to find some additional replies on what this option value actually means, but unfortunately I didn't.
I did some googling and found the description which points me to the protocol page where the option values is explained as:
option_value.jpg
But this does not make and sense to me because the options I have are: T-Rate, Option, Rate.
And they all have varying ranges for example T-Rate:
Starts at (holding the + button until it reaches an endpoint)
50 -> 125 -> jumps to -126 -> -1 -> jumps to 4 -> 124 -> jumps to -127 -> -112 and then goes over into option 71.
Why are these ranges not consecutive?

I also checked the debug screen, and the invalid packet counter is rising, but way slower than the total packet counter.
(in this picture the total counter has overflown a couple of times)
debug_stats.jpg
But one thing did make me uncomfortable, the debug screen locked my TX. I was still able to give stick commands but the menu/exit buttons didn't do anything anymore and it froze on the debug screen. Is it possible that the invalid packets may somehow result in a programming corner case? Or may the untested debug firmware have caused this? I do like the telemetry statistics over the normal statistics screen, so I can at least see that something is coming in.

So long story short:
1. TSSI values seems incorrect.
2. Is there any logical documentation about the option value?
3. Is the debug firmware considered stable, or is it better to flash the latest normal build?
4. Is there a way to embed the telemetry (DEBUG) screen in the normal statistics?
5. display and asterisk when telemetry is received just like OpenTX does?
6. Is a slowly increasing error counter to be expected, or is this a no-go?
Last edited by Timeless on Mon Aug 17, 2020 9:43 pm, edited 2 times in total.

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MikeB
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Re: er9x and multi-protocol telemetry mod

Post by MikeB » Mon Aug 17, 2020 7:11 pm

nvd07: Between telemetry packets is the blue trace from the module idling high or low? If inverted, it should be low.
I know some modules from some manufacturers had a 7400 chip instead of a 7486 and so don't invert the signal properly.

Mike
erskyTx/er9x developer
The difficult we do immediately,
The impossible takes a little longer!


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