ELRS No Telemetry data displayed for HoTT

[ripe timber]

I was not able, to make HoTT Telemetry working for me. I Tried the following hardware (all with the latest official ELRS Release 3.4.3)

• BetaFPV 5CH Micro receiver using CH2 (TX) only or CH2 (TX) and CH3 (RX) with a diode cable
• BetaFPV Super P14 Receiver using CH14 (TX) onbly or CH14 (TX) and CH13(RX) with a diode cable
• RadioMaster ER6 RX/TX Port using TX only or RX/TX with a diode cable
• Horus X10S Transmitter using an external ELRS module
• Radiomaster Zorro ELRS Transmitter
• Graupner HoTT Vario Sensor 33601

Only the receivers telemetry data are displayed and no Vario telemetry can be found.
I Logged the serial communication and everything seems fine (Sensor answers after 80 89 request):

8c 80 89 7c 89 00 90 00 f5 01 f6 01 f4 01 3a 75 1c 75 30 75 00 00 00 00 00 00 0
00 00 00 00 00 00 00 00 00 00 00 00 00 00 7d d9 80 8e 80 8d 80 8c 80 89 7c 89 0
01 f4 01 3a 75 1c 75 30 75 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0
00 00 00 7d da 80 8e 80 8d 80 8c 80 89 7c 89 00 90 00 f6 01 f6 01 f4 01 44 75 2
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 7d ee 8
80 89 7c 89 00 90 00 f6 01 f6 01 f4 01 44 75 30 75 30 75 00 00 00 00 00 00 00 0
00 00 00 00 00 00 00 00 00 00 00 00 00 7d f8 80 8e 80 8d 80 8c 80 89 7c 89 00 9
f4 01 26 75 3a 75 30 75 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0
00 00 7d e4 80 8e 80 8d 80 8c 80 89 7c 89 00 90 00 f6 01 f6 01 f4 01 44 75 44 7
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 7d 0c 80 8
89 7c 89 00 90 00 f6 01 f6 01 f4 01 30 75 4e 75 30 75 00 00 00 00 00 00 00 00

No Idea, what I am missing...

[umbral finch]

Did you change the pin assignment in the hardware.html page ? And set the serial protocol to HOTT ?

There is some doc here > https://www.expresslrs.org/software/serial-protocols/#hott-telemetry-notes

[ripe timber]

I changed the appropriate channels to Serial Rx and Tx in the "Model" Pane of the WEB configuration and selected HoTT Telemetry as the serial protocol.
I did not chhange the hardware configuration, i.e. I did not remove the two pins from the PWM output pins configuration. It is not quite clear for me from the documentation, if this is required or not.

PS: CRSF Serial pins: RX pin and TX pin in the hardware configuration are empty.

[umbral finch]

This should not be required. Only setting the pins to Serial Rx/Tx is.
Are you using EdgeTx ? If yes, did you try deleting all signals and discovering them again?

[ripe timber]

I am using EdgeTx and deleted all sensors and tried to discover them new. Only the sensors from the Receiver came up.

Studying the code in ELRS GitHub, I found it strange, that SerialHoTT_TLM::processBytes expects sizeof(hottBusFrame) bytes, which includes the two (echo?) bytes from the request (e.g. 80 89). I opened an Issue for that (https://github.com/ExpressLRS/ExpressLRS/issues/2909) but the author said, it works as expected and required.

[umbral finch]

It looks like another user already managed to have a working hott sensor here: #1259284557782454272 message

Maybe compare this config with yours ? I sadly don’t have any hott sensors to help you further.

[ripe timber]

THX for your help. In one of 100 cases, the Vario is detected after deleting all sensors and searching them again, but does not update its values regulary after. In my opinion, HoTT telemetry for ELRS does not work reliable for now. I created the Arduino OpenCRSFSensor Project, which works without any problems, but HoTT seems to be very picky, considering timing etc. ☹️

[wise void]

No, it's not, it's working fine. For the lack of a 8285 based PWM receiver I just set up my 8285 BetaFPV Nano RX running 3.4.3, using the 33601 Vario and the required Schottky diode. I suspect a wiring problem. Please checkout the wiring diagram. The signal wire of the HoTT sensor needs to be connected to RX, the diode needs to be placed between RX and TX with the black bar facing TX.

Attached find the wiring diagram, my nano RX wiring (pinout RX TX 5V GND), note the signal wire is connected to RX and note the orientation of the diode (needs to be a Schottky diode, e.g. BAT43), a scope screenshot showing correct bus master and slave response timing and a short video of values updating.

[wise void]

And please do me a favor. Read https://www.expresslrs.org/software/serial-protocols/?h=hott+te#hott-telemetry-notes and understand the differences between ESP32 and ESP8285 based receivers. ESP8285 receivers need the diode setup, ESP32 receivers like the SuperP 14ch or ER6 don't. You connect the HoTT Telemetry sensors signal pin to the TX pin directly. A diode between RX and TX won't work on ESP32 receivers but is required for ESP8285 receivers (e.g. BetaFPV 5ch)

Concerning echo bytes: Combining RX and TX through a diode to transform the full duplex serial to half duplex single wire serial (as required for ESP8285 receivers) leads to sent bytes are also received concurrently. This is the reason why you have to take the echoed bytes in account. Sending out a 2 byte command followed by the sensors 45 bytes response will lead to 2+45 = 47 received bytes.

[ripe timber]

Unfortunateley, I don't know, what chipset the Betafpv Micro 5CH receiver actually has, so I tried both variants (with or without Schottky diode)
Neither variant worked.
I can not imagine a wiring problem, especially for the BetaFpv Super 14. Plugged the sensor directly to the Serial Tx configured channel...
Strange, that sometimes the sensor is detected but mostly not. Even, if detected, it is not updated on the transmitter.

[wise void]

There might be exceptions but generally receivers with 5 or less PWM outputs are 8285, receivers with 6 or more are ESP32 based.

Are you sure you have your 33601 Vario on the latest firmware version? It might be a very old HoTT V3 firmware.

Let's start with the SuperP. Show screenshots of the entire WebUI and /hardware.html. Also a photo of how the vario is connected to the SuperP.

[wise void]

Module and receiver on 3.4.3. Channel 13/14 set to Serial RX and TX, Protocol selected: HoTT Telemetry. Vario is on 1.20 (latest)

Example RF settings. What's your packet rate and telemetry ratio?

[ripe timber]

Modules and receiver are on Version 3.4.3, Channels 13/14 on BetaFPV SuperP 14 are setup for Serial, Protocol set to HoTT and 19200 Baud.
I don't know the firmware Version of the Vario an will not be able, to be in my Workshop till end of September, since I am abroad now. I will deliver the required screenshots and photos as soon, as I am back, sorry.
Other informations, which may be interesting for you: I use the EU_LBT setup and 100 Hz full mode and Standard Telemetry packet rate (although I experimented with different TLM rates too).
Thanks for your help.

[wise void]

Everything is still on the bench so I updated module and rx to 3.4.3 EU_LBT, 100Hz full and telem ratio std (which is 1:32). 1:32 yields a bit rate 173bps@100Hz. Evrything telemetry is slow now but still works. Shouldn't make a difference but just out of curiosity: which radio (and fw version) are you using.

[wise void]

Just to be sure, here's a screenshot showing the bus activity for the SuperP with the 33601 connected on the physical layer. 0/1 levels look good, timing looks good.

btw: a reasonable telem ratio for 100Hz full is 1:4 or 1:8 if you want a decent response of your vario.

[ripe timber]

Thabks for your tips.
I tried it with a Horus X10 and a Radiomaster ELRS Module and a Radiomaster Zorro native ELRS Transmitter. Both Transmitters running EdgeTX latest official version 2.10.4.
For now, I suspect the firmware version of the Vario. Can not check or update at the moment...

[wise void]

Any other HoTT sensor to try? Unisens?

[ripe timber]

Sorry, this is the only HoTT sensor, I have...

[wise void]

The 33601 is one of the first sensors Graupner sold for HoTT ages ago and some time before switching from V3 to V4 protocol. Might well be.

I always wondered why Graupner radios don't send the two polling bytes back to back. Instead they send polling bytes at 1ms intervals (leaving about 400us gaps between byte 1 and 2). Didn't make sense but the reason is this Vario. It has a very slow micro with obviously no FIFO. This Vario wouldn't work with my implementation at first. Everything else would. I remembered the gap, changed my implementation. Vario worked. This Vario is really the slowest of all possible sensors. The ELRS implementation is now exactly mimicking the genuine Graupner radios implementation.

[ripe timber]

Will try to update the sensor, when I am back at home.
To verify the sensor, I wrote a short Program for an Arduino ESP32 and was able, to get the sensor values.
Can not do anything more from here sorry, writing everything on my mobile, internet is also a pain 😆

[ripe timber]

Today, back to the workshop, I updated the 33601 firmware.
Now it works like a charm! I tested with a "BetaFPV SuperP 14" channel Rx using a "direct connection" on Tx and with a "BetaFPV Micro" 5 channel Rx with a diode cable. Both configurations worked perfectly.
Telemetry rates of 1:4 or 1:8 seems to be good values for a quick response. Thank you very much for your support.

[wise void]

You're welcome