Hands on: E45-TTL-100 868MHz LoRa wireless modules

My quest for ultimate (?) DIY telemetry system for UAVs continues. Last year I was playing with HC-12 433MHz wireless modules with pretty decent results. After all, more than 1km of range for a few bucks is more than acceptable. Still, HC-12 has at least few problems:

  • 433MHz band is very often polluted and used by other Rc systems/subsystems (LRS)
  • 433MHz requires pretty big antennas
  • No frequency hopping
  • No easy way to build network of more than two HC-12
  • 1-1.5km of range is nice, but one might want more

Chengdu Ebyte E45-TTL-100 868MHz LoRa serial wireless module

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FrSky SmartPort Telemetry on AnyFC F7

STM32F7 CPU family present in newest, experimental, flight controllers like AnyFC F7 (as well as upcoming AnyFC M7 with smaller STM32F722) simplifies many things. For example, comparing to F4 boards, SmartPort or S.Bus connection is extremely simple and can be done on any free UART. No more hardware hacks, external inverters and other “special” ways of doing things.

It’s super simple again, and here is how to do it in Betaflight (Cleanflight 2.x) and INAV

Hardware

The only required hardware is a cable to connect SmartPort enabled receiver with free UART port on F7 board. This will work on X8R, X6R, X4R, X4RSB, XSR and any other. The trick is to connect S.Port pin with UART TX pin only.

How to connect F7 flight controller to SmartPort

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Talking Taranis – teach FrSky Taranis to talk to you

One of the most important features of modern, computerized, radios is that you can make them talk to you. After all, with setup telemetry link from UAV, radio should “know” things. Things like battery voltage for example. Why not make FrSky Taranis (or Horus or Taranis X Q7) talk to you and report LiPo voltage in a smart way?

Before we proceed, you have to setup SmartPort telemetry or “legacy” FrSky telemetry. This post does not covers this topic. You might want to take a look here and here.

Let’s go

In OpenTX menu navigate to last page called Telemetry and check if VFAS is reporting proper value.

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3D Printed HC-12 and HC-06 telemetry relay box

It’s a very nice feeling when people starts to create accessories for your inventions. OK, maybe “invention” is too strong word here, but still.

EduardoChamorro designed a 3D printed case for my HC-12 433MHz to HC-06 Bluetooth bridge that I published here last year.

LRS to Bluetooth 3D Printed case

It’s small, it has a switch and status LED. It also has integrated LiPo battery and a charger. Awesome!

Project can be downloaded from Thingiverse.

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3D Printed 433MHz Moxon Antenna With Arm And Snap Mount

It’s still middle of winter here in northern hemisphere, but I’m slowly preparing for next flying season. One of my goals is to push my DIY HC-12 Telelemetry System to a next level. In both range and quality. For quality I’m planning small hardware LTM decoder with LCD. For range, I want to reach at least 1.5km with 9600bps FU3 mode and 2.5km with 1200bps FU4 mode.

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SmartPort inverter for F4 flight controllers

While STM32F4 family processors installed in newest flight controllers are superior to STM32F3 (and F1 of course) in terms of raw speed, they are inferior to F3 family in terms of IO handling capabilities. For example, F4 family is not equipped with UART port inverters. And that creates a series of problems when it comes to connecting various serial RX receivers and telemetry systems.

The most popular FrSky (Futaba) S.Bus serial RX protocol and FrSky SmartPort telemetry require inverted UART signal. If there is no hardware inverter on hardware UART port, they will not work. While S.Bus requires only one data line, external inverter is not a big issue. Some time ago I’ve published The Simplest Harware Inverter. One MOSFET transistor, one resistor and that’s all.

In case of SmartPort, it’s slightly more complicated. Not only signal is inverted, SmartPort also combines TX and RX UART line into single wire. That means the following:

  1. More complicated inverter is required
  2. Software has to support this case and fallback to unidirectional UART mode

Hardware

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Simplest hardware inverter for flight controller

Together with increasing popularity of STM32F4 flight controllers, telemetry became hard topic again. Why? Most popular telemetry protocols, SmartPort and FrSky telemetry , requires inverted signal. Zero becomes one, one becomes zero.

In case on STM32F3 that was not a big problem. Those CPUs have built in inverters. STM32F1 and STM32F4 does not. So, if flight controller designer did not put external inverters on UART ports, FrSky telemetry, SmartPort and even S.Bus would not work.

Luckily, simple inverter for FrSky telemetry and S.Bus can be build using only few electronic parts:

  • Small logic level N-channel MOSFET transistor. One of the best choices is 2N7000
  • 10kOhm resistor
  • few cables

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INAV 1.1 for Naze32 with working telemetry

As long as Naze32 / Flip32 are decent flight controllers for those who does not demand too much, they share very big flaw: low flash memory size. While even a year ago 128kB of flash was enough, times changed, and limited flash makes a problem for advanced flight controller software like INAV. Starting from INAV 1.1, STM32F1 flight controllers started to pay a penalty of disabled features. That time it was "only" telemetry providers other than LTM. Next time it might / will be more.

During last few weeks I've received few request to compile INAV 1.1 with enabled FrSky and/or SmartPort telemetry on Naze32 target. While I have nothing against doing that on request, I've decided it would be better to just prepare special version of INAV 1.1 for Naze32 users with all telemetry providers enabled. Link to ZIP file is at the bottom of this post.

  • This version has LTM, FrSky, SmartPort and HOTT telemetry enabled
  • To fit telemetry in limited flash memory, following features has been disabled:
    • OLED display support
    • DJI NAZA GPS module support

INAV 1.1 for Naze32 with telemetry enabed

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850m for $20

Short update on my DIY telemetry link for $20 from my previous post. In theory, it should be able to work up to 500m. Today I archived range of 850m. And I’m pretty sure it’s not the end if I was flying higher. At this distance signal was attenuated by 1st Fresnel zone. Next time, more altitude and higher mounted receiver antenna!

850m for $20

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