Arduino hygrometer with DHT11 and SSD1306 OLED display

One of the things I like about Arduino ecosystem is that you can prototype pretty decent device in very short time. It might not be pretty, but will work. Just like my DIY hygrometer built with DHT11 and SS1306 OLED display I've built few weeks ago:

Simple, efficient and runs on 4 AA batteries. The best part is that it can be powered all the time. Arduino does humidity measurement, display the result and then powers itself down to conserve power. Cool, right?

Arduino DHT11 hygrometer with OLED SSD1306 display

Code is available in GitHub repository.

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Crossbow LRS, hardware

Weather outside is bitchy. Period. It rains, then it's windy and then maybe there is some direct sunlight for 15 minutes. No way to fly or test my DIY RC radio link.

Weather is bitchy

But, there is some progress after all. My latest changes seems to be working just fine. On a bench link was stable for almost 3 hours. Later I too it for a standard range test: 2.8km LOS. It also worked, I still had around 5dB of link budget left on a ground level.

Back to the topic. Crossbow LRS is open source and open hardware. Maybe open hardware is too much, since there is almost no hardware to build. After all, first iteration is based on LoRa32u4 II development boards and running good old Arduino.

RX module requires no additional hardware:

Crossbow LRS receiver module

TX module is slightly more complex. It required voltage stabilizer and inverter/level shifter made with single 2N7000 FET transistor. I2C OLED display is an option:

Crossbow LRS transmitter module

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Hands on: LoRa32u4 II 868MHz LoRa development board

Idea for Crossbow, DIY LRS system did not appearned in my mind out of nowhere. All my previous LoRa attempts were aimed at telemetry purposes only. E45-TTL-100 are cool, but bulky. If I would want to use them, I would either have to attach Arduino to it or hack it open and reprogram onboard CPU (like Qczek LRS does). Somehow it was not something what suited me very much.

But then I came across Adafruit Feather LoRa32u4 RFM95. Awesome idea. ATmega32u4 and HopeRF RFM95 LoRa module on one PCB, Arduino compatible, reasonably small and light. As a bonus, can be LiPo battery operated and has own 1S LiPo chanrger. The only thing I did not liked (OK, not the only one, but that was the biggest one) was price tag: $34.95 is somehow slightly more than I'm willing to pay for ATmega32u4. Even with radio module. So, after some digging on eBay I've found something that looked like a clone of Adafruit Feather LoRa32u4 RFM95: BSFrance LoRa32u4 II.

LoRa32u4 II 868MHz LoRa development board

BSFrance LoRa32u4 II 868MHz LoRa development board

Continue reading “Hands on: LoRa32u4 II 868MHz LoRa development board” »

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Testing 868MHz LoRa range, part 3: round trip

After determining that range of 868MHz LoRa wireless modules E45-TTL-100 have, at least, quite impressive range (5,7km and I was out of line-of-sight to test further) I’ve decided to test something else.

In the beginning I was planning to use those radio modules for telemetry only, but then another thought crossed my mind: why not to build DIY TBS Crossfire for the poor? After all, TBS Crossfire also uses 868MHz LoRa (SX1272 vs SX1276), so it should be possible to build DIY radio link for medium range (up to 5km) for RC planes, right?

First of all, I will need to know how fast data can be transferred and how much delay can I expect in real life. So I’ve modified Arduino code and E45-TTL-100 configuration:

  • UART speed bumped from 9600bps to 57600bps
  • air speed bumped from 2400bps to 19200bps
  • output power lowered from 100mW to 50mW (17dBm)
  • transmitter sends 5 bytes of data (current microseconds and prefix)
  • relay receives packet and resends it to transmitter
  • current received number is deducted from current microseconds and round trip time is showed on OLED display

LoRa E45-TTL-100 round trip test

Results:

  • Round trip time is 82ms on average and it does not changes with distance
  • at lower output power (50mW vs 100mW) reception at 2.8km is worse. 100% of packets are received only then antenna alignment is not worse than 45 degrees
  • with slightly bigger payload size (up to 7 bytes) it should be possible to archive at least 20Hz update rate

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Quick note on SEMTECH SX1276 100mW output mode

Few facts about SEMTECH SX1276 LoRa modem and 20dBm (100mW) mode:

  1. +20dBm (100mW) is possible only on PA_BOOST pin
  2. Pins RFO_LF and RFO_HF allows only up to +17dBm (50mW)
  3. Maximum allowed duty cycle while using +20dBm mode is 1%
  4. Maximum allowed VSWR while using +20dBm mode is 3:1

The biggest problem with +20dBm on PA_BOOST is allowed 1% duty cycle. On the other hand, +17dBm mode (50mW) does not have such a limitation and maximum range should be only 1.42 times shorter than in 100mW mode.

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Hands on: Tiny Frsky 8CH Receiver from Banggood

I have a nasty habit of buying things and then forgetting about them. Something like that happened to Tiny Frsky 8CH Receiver (Wolfbox F802 software compatible) from Banggood I’ve purchased last year. For some time I used it in JJPro P175 quadcopter, but then it landed in a box and I forgot about until last week.

Tiny FrSky 8CH DIY Receiver Pinout

So, let’s do overdue “hands on” on Tiny Frsky 8CH Receiver from Banggood… Continue reading “Hands on: Tiny Frsky 8CH Receiver from Banggood” »

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Testing 868MHz LoRa range, part 2: open space

It was a good weekend. At least for me and CDEbyte E45-TTL-100 868MHz LoRa serial wireless modules based on SX1276. Why? Since weather was nice and looks like those modules are way better than datasheet specifies. Specs states: 3km in open space. And I’ve proven almost twice that much range! Last Friday I’ve placed one E45-TTL-100 with stock antenna on my balcony, took second with me and went for a car ride.

E45-TTL-100 LoRa 868MHz range test results

Area around my home is full of small hills and copses, so most of the time something was blocking the line between transmitter and receiver. But every time I was high enough, I was getting clear signal without any packets lost. At the furthest point of my trip I was 5.7km from the transmitter, inside a car and a copse was between me and TX module. That means no line-of-sight and as a result I’m pretty, pretty sure E45-TTL-100 should be able to work on much higher range that that. I only have to find a good place to test it.

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Testing 868MHz LoRa range, part 1: urban area

With a (more less) free evening I decided to finally start testing range of 868MHz LoRa E45-TTL-100 radio modules I described only yesterday. Instead of building new testing rig, I only upgraded testing setup I used to test range of FS1000A and XY-MK-5V 433MHz radio modules. Few hours later I came up with this:

LoRa range testing equipment

  • E45-TTL-100 at 9600bps, transparent serial mode
  • Stock (crappy) antannas
  • Logic driven by Arduino Pro Mini
  • Transmitter send 1 byte counter
  • Receiver counts packets and check if all subsequent packets arrived and then displays results on OLED screen
  • Powered from 2S LiPo batteries

I’ve left transmitter on a desk and went for a walk. Even before leaving the building radio signal had to cross around 1 meter of bricks. Then travel through another building and only then go into the direction when I walked.

LoRa range in urban area with E45-TTL-100

I must say: I was impressed. I still am. At 511 meters transmission was clear only when I was not blocking it with my body. Or standing near to metal fence. So I can safely assume: 500m is maximum range in densly populated urban area. On stock antennas and 100mW output power. Next week I will try stronger, dipole antennas.

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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

Continue reading “Hands on: E45-TTL-100 868MHz LoRa wireless modules” »

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FS1000A and XY-MK-5V second range test

Two months ago, when I published first FS1000A and XY-MK-5V range test, I was little surprised that I was able to reach 315 meters of stable connection. And I was almost sure, that they can do more.

Having some free time during my summer vacation, I’ve left transmitter on a towel and took a walk with a receiver. In a surroundings just like that:

FS1000A XY-MK-5V test on a beach

Results? 332 meters with a FS1000A powered with 7.4V and 1000bps over-the-air data speed.

FS1000A XY-MK-5V range test on a beach

For the second time, I’m sure I can pull more from this setup. This time, there were two problems:

  1. Transmitter was low on the ground
  2. Other people on the beach blocked line of sight much faster than I expected

So, expect third attempt…

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