Lora Messenger - Page 1
Forum section: electronics / rf-microwave

author: neilhao
author_rank: Regular Contributor
timestamp: July 10, 2021, 11:27:09 pm
content: I designed a Lora Messenger which does not depend on Internet or Cellular network. In other words, users can chat with others by using this credit card size Lora device and a smartphone with Bluetooth without Internet and Cellular network.For the hardware design, a high efficiency compact Lora PCB Antenna and an ultra-low noise figure amplifier had been designed to maximum the communication range.For the software design, a simple Lora half duplex communication protocol had been implemented by about 600 lines of C++ code.Current testing firmware implemented:Lora half duplex communication protocol with timeout and re-transmitting featuresBluetooth Serial Port Profile (SPP) which provides communication capability between the phone and the Lora device.Command Parser for executing user commands through Bluetooth.The coverage of this credit card size Lora device was tested. In the experiment (TX:14dBm, Freq:915Mhz, Spreading Factor:12), 1500m communication distance had been tested, no timeout or re-transmitting occurred. According to the link budget, this system could reach far further than 1500m.Demo VideoProject Page:http://uniteng.com/wiki/doku.php?id=loramessenger:project

author: Skashkash
author_rank: Regular Contributor
timestamp: July 11, 2021, 12:50:14 am
content: That's pretty neat.Add a driver for ATAK, and you could probably sell a pile of them.

author: neilhao
author_rank: Regular Contributor
timestamp: July 11, 2021, 12:34:14 pm
content: Quote from: Skashkash on July 11, 2021, 12:50:14 amOriginally, I just intended to design a low power emergency communication system for traveling and hiking, e.g., Death Valley National Park. I planned to design a long range UWB position system as the next project which could help people to find each other. However, I did not know a good APP which could be used as a framework for information integration.ATAK looks powerful and funny, thank you for your suggestion! I will dig into it, maybe we will finally have a community project on Github~

author: Skashkash
author_rank: Regular Contributor
timestamp: July 11, 2021, 05:03:37 pm
content: There is also meshtastic.https://meshtastic.org/But I've not seen any decent hardware implementations for it.You have a little extra real-estate on your PCB, you could maybe add an optional gps receiver.But if the idea is that it'll always be used with a phone that has gps built in, maybe not needed.

author: Lord of nothing
author_rank: Super Contributor
timestamp: July 22, 2021, 09:16:12 pm
content: Well I want do some similar but just with DMR and PMR446 DMR Radios who can send and receive "SMS" (from Radio to Radio). For that I got a MMDVM_HS_Dual_Hat refuse to work right now.The major difference is on PMR446 is no real Transfer Cap. On the "licence free", ISM Bands are just <10% duty Circle that mean after sending a Message you may have to wait 6 Minutes or so until you can send another Message.Well that sucks...Another problem is the very low Output Power like <100mw when a PMR446 Radio can transmit with up to 500mw just a view Mhz above the 433Mhz.How does your System Avoid taht?

author: neilhao
author_rank: Regular Contributor
timestamp: July 23, 2021, 03:37:41 pm
content: Nope, Lora also has no collision avoidance capability (Listen Before Talk) by default, it uses duty-cycle. Thus my simple communication protocol will wait randomly several seconds before resenting a timeout message.Quote from: Lord of nothing on July 22, 2021, 09:16:12 pm

author: georges80
author_rank: Frequent Contributor
timestamp: July 23, 2021, 05:26:33 pm
content: Quote from: neilhao on July 23, 2021, 03:37:41 pmYou can use the Lora CAD to check if a 'channel' is free before transmitting. It isn't 100% since two radios may check CAD and then simultaneosly attempt to transmit. One improvement would be to add some random time after CAD shows the channel to be free before transmitting.The CAD is not perfect, but it at least helps in competing stronger signal situations.cheers,george.

author: Lord of nothing
author_rank: Super Contributor
timestamp: July 23, 2021, 06:32:09 pm
content: QuoteWell I mean you can send only X Messages per Hour before you hit the duty Circle you must follow and wait.When I use my PMR446 Radio I dont have any duty Circle or anything the only rule is a Transmission can only last for 90sec at the Time before the Radio must shut off until you hit the PTT Button.Since the Messages are Digital the are so small and short and last only some seconds.If am be insane I could send 24/7 Messages total legally.Well the only "problem" is your device must be follow the rules and regulation and you must declare it does so.You are not the first Person who tought he could make such a device and fail because you also must follow the regulation and the suck from time to time.

author: Skashkash
author_rank: Regular Contributor
timestamp: July 24, 2021, 04:34:35 pm
content: lorawan has duty cycle limits.https://avbentem.github.io/airtime-calculator/ttn/us915-dl/64In the USA, does the FCC specifically limit transmission duty cycle for the ISM bands?Why would lora be treated different than wifi (for instance)?

author: Lord of nothing
author_rank: Super Contributor
timestamp: July 24, 2021, 07:15:41 pm
content: Since the use 433Mhz, 868Mhz but not 2,4Ghz or 5Ghz like Wifi.

author: georges80
author_rank: Frequent Contributor
timestamp: July 24, 2021, 07:42:16 pm
content: 1) The OP stated he wrote a half duplex stack, he is NOT using lorawan2) The US does not impose a duty cycle limitation on the 900MHz ISM band3) End of hypothetical issuescheers,george.

author: Skashkash
author_rank: Regular Contributor
timestamp: July 24, 2021, 08:55:38 pm
content: Quote from: georges80 on July 24, 2021, 07:42:16 pmYep, that is what I thought. lora modulation != lorawan.I'm working on a proprietary lora project myself using a SX1262 (USA, 900mhz) and never saw any duty cycle limitations.But you do need to go over part 15 with a fine comb for this stuff.

author: neilhao
author_rank: Regular Contributor
timestamp: April 07, 2022, 11:41:50 am
content: I just ported this design to Meshtastic, because Meshtastic comes with excellent android and iOS APP. Additionally, it also have a software plugin for ATAK (https://meshtastic.org/docs/software/community/community-atak).More Details:https://uniteng.com/wiki/doku.php?id=meshtastic:nano