Non bluetooth radio IC - Page 1
Forum section: electronics / projects

author: kuon
author_rank: Regular Contributor
timestamp: January 07, 2024, 02:38:14 pm
content: Hello,I am working on a wireless sensor and for radio we use Bluetooth.We have a few problems with it:- we are starting to install our sensors in areas where more range would be a nice plus, especially indoor through walls- frequency is crowded is some areas- people passing by with phones are sometime flooding our devices with requests, even without being paired- the protocol is complicated, I don't think I really understand it even after working with it for three years- we already been hit twice with component shortage and changing module required a lot of work, I know it was covid, and might not happen again, but it is part of the frustrationThe requirements are quite simple, I have short messages < 256bytes I send periodically, about 3 per minutes.The scenario would be something like this (protocol wise):Controller and sensor would both have the same radio module and MCUMCU <-> Radio IC over IC2, SPI or UARTOn controller:MCU - Radio IC-> listen to message starting with 1234 on channel 1<- OK-> listen to message starting with abcd on channel 2<- OKOn Sensor:MCU - Radio IC-> send 12345678 on channel 1<- OKOn controller:MCU - Radio IC<- interrupt-> read last message<- 12345678-> anymore message?<- NOWe do not need encryption. Our messages are encrypted on the MCU using a higher level protocol already.The controller side should be able to listen to a few different sensors, 20 would already be enough but to be future proof <128 would be ideal.I don't know if the 868Mhz band would be a good choice (we are in europe) and which device to use. Most radio IC I found in this band tend to be not recommended for new designs.

author: Buriedcode
author_rank: Super Contributor
timestamp: January 08, 2024, 07:58:32 pm
content: Well 433.92 and 868 MHz are the two common non-2.4GHz bands.For 433Mhz there are plenty of "dumb" transmitter/reciever pairs, which are often used for simple remote controls, but I would avoid them as you would have to implement pretty low level channel coding (manchester encoding, error detection/correction, packet handling etc..) on the reciever end as they just output raw noise all the time.CC1101 is an old device, but is reliable and has plenty of libraries on every platform. The RFM69** series modules are great too, I believe these are based off the similar family of transciever chips like the SI4432. All of these are pretty much digital -> Antenna, which means the matching, LNA, Tx power amp and all the analogue is on the module and done for you, just leaving the host to communicate with the module to configure all the parameters are startup, and to set to transmit, reiceve, sleep etc.. (all via an SPI-like interface, @3.3V).They're all transcievers, and have the facility to auto-acknowledge so you can just fire off a packet, and the reciever can request a resend if there are errors virtually guaranteeing a good link (within range).The downside is they can be quite complicated - you have to set the frequency, channel, bandwidth, datarate, line coding, packet length preamble etc..etc.. but once you have that decided, its easy and only has to be set on power-up (when put to sleep the modules retain this config).As to 433.92 vs 868, the former is much more popular, and therefore crowded, but its also only used by short-duty devices that fire off a short packet every so often, so theres unlikely to be constant interference. I've found the 433.92 modules to give better range than the 868 one with the same power setting - but there are so many variables that could just be my location or the building I tested it in.Note: Whilst most of the above module's ICs allow for a very wide frequency range,the modules on-board passives are tunedto a specific band - using a "433MHz" RFM module for 868MHz will most likely give terrible range, and visa versa, so you can't really just switch between the two.Edit: Just realised, if you have an external antenna on the sensor (via uL pigtail?) and want to stick to 2.4GHz, then the NRF24L01 modules are ubiquitous, cheap, and a similar deal to the above. Might struggle to go through floors though as the maximum power output on the "vanilla" modules is pretty low (0dB) where-as the 433/868 modules tend to have configurable power output up to 10dB which I've found to go through a couple of floors in a building.

author: tszaboo
author_rank: Super Contributor
timestamp: January 08, 2024, 08:38:07 pm
content: A lot of BT chipsets can be used in 802.15.4 mode. Or they have a variant that has it. So a phone cannot connect to it, and you are free to send whatever format in your message. And you don't need to redesign everything. The range can be fixed with a little bit more power, or little bit more sensitivity.

author: Benta
author_rank: Super Contributor
timestamp: January 08, 2024, 08:55:31 pm
content: ZigBee comes to mind. Will run at 2.4 GHz and 868 MHz.

author: kuon
author_rank: Regular Contributor
timestamp: January 09, 2024, 03:10:24 am
content: Thanks for the suggestions. I didn't know ZigBee had a 868Mhz variant. I tried the Xbee from Digi, but we had reliability problems. Do you have specific module to recommend?

author: robert.rozee
author_rank: Frequent Contributor
timestamp: January 09, 2024, 03:50:54 am
content: HC-12 modules are a simple option: 433MHz band, up to 100mw as i recall, several channels available, present as TTL-level RS-232 at both ends, so you can communicate in both directions. people use them for a variety of things, some even as mesh networks!cheers,rob :-)

author: Psi
author_rank: Super Contributor
timestamp: January 09, 2024, 03:54:46 am
content: If moving from 2.4g Bluetooth to a lower frequency like 433mhz be sure to consider the antenna differences, size etc.For a small device I found 2.4ghz more workable than 433mhz.There are options for small antennas at 433mhz, like little specialized SMT ones, but that adds cost vs a simple and free PCB antenna at 2.4ghz

author: MarkT
author_rank: Frequent Contributor
timestamp: January 09, 2024, 10:47:55 am
content: For longer range longer wavelength is preferrable - but you need the antenna to match... 2.4GHz is problematical as one microwave oven with a leaky door could ruin your day, unless you use spread-spectrum (like WiFi). The legal ISM bands vary by territory, note, so check that.

author: kuon
author_rank: Regular Contributor
timestamp: January 09, 2024, 09:31:46 pm
content: Quote from: MarkT on January 09, 2024, 10:47:55 amHere 868Mhz is the preferred frequency apparently. The device should be large enough to host a regular quarter wave antenna, but as it was said, there are some SMT antenna that resonate at this frequency (how they work is a bit voodoo to me, but they got good application notes).

author: Benta
author_rank: Super Contributor
timestamp: January 09, 2024, 10:47:18 pm
content: Quote from: kuon on January 09, 2024, 09:31:46 pm868 MHz is a much quieter band than 2.4 GHz, where everything else is (microwave ovens, BT, WLAN and all sorts of other junk.)868 is mainly car keyfobs, garage remotes etc.The SMD antennas were described to me by an RF friend as "leaky resonators. Basically an attenuator, but better than nothing."If you can, go for a real 1/4-wave antenna, it's around 8 cm at 868 MHz.An alternative could be an inverted-F antenna etched on your PCB:https://en.wikipedia.org/wiki/Inverted-F_antenna

author: Buriedcode
author_rank: Super Contributor
timestamp: January 10, 2024, 02:00:24 am
content: Stubby Antennas for 868 can be around 40mm, with *claimed* gain of 2dBi (I'm assuming thats with a nice big flat ground plane).Ultimately though, what works in what situation, can be hard to predict given the many variables. I say just pick a band (be it 2.4Ghz but another standard, 434/868 etc..) run a few tests, and keep in mind it might not be satisafactory, in which case you try another band. The time and cost of equipment to check for constant/intermittent interefence in places with dynamic activity, is a lot, so having a cheaper backup - pereferably once that uses the same firmware/software - to speed up development is handy.

author: bookaboo
author_rank: Frequent Contributor
timestamp: January 10, 2024, 07:07:44 am
content: If this is a commercial application, now would be a good time to discuss with your local compliance test house. The ISM bands have various limitations placed on them, depending on the exact frequency. You will likely be limited by tx power and duty cycle…. Best find out now if you can’t send as many messages as you would like.Keep in mind that a gain antenna on a transmitter could cause you to fall foul of the regulations. You may be within the tx power limits, which are isotopic, but if you add a gain antenna then there’s a chance you are directing more than permitted power in that plane/direction. Receive antenna have no such limitation.

author: pcprogrammer
author_rank: Super Contributor
timestamp: January 10, 2024, 09:07:28 am
content: There is the NRF905. It is also an older device, but works rather well and is simple to use. Message length is only 32 bytes per transmission and kind of fixed with a setting that has to be the same on both sides. So if you need to send more then 32 bytes it has to be done in chunks and all the messages need to have the same length.It is suited for both 433MHz and 868MHz bands. You can find modules with this chip on Aliexpress and Amazon, where they advertise them as 433/868/915MHz capable, but most of them are setup for 433MHz. It depends on the antenna balun components.I have a bunch of them to play with and testing showed that they only work on the one band the module is setup for.(Edit: All of them 433MHz in my case)Might be a bit of a pain in the bum to set it up for receiving from multiple sensors, but a polling system done by the master can easily solve this. Each sensor would need a unique 32 bit address though. The master can setup an address of a sensor, send a request message to the sensor and then wait for a response and process it. Then try the next sensor, etc.The sensor would need to be in listening mode until it is addressed and when it receives a valid request from the master reply with its reading. An acknowledge can be added of course to make it a bit more robust.A 10 byte message takes about 3ms to transmit.Check out thedatasheet.

author: kuon
author_rank: Regular Contributor
timestamp: January 11, 2024, 10:55:06 pm
content: I am going to test the CC1101. I read the datasheet and it seems to be adapted to my needs.I have already contacted my local certification lab and they will help me ensure the device can be certified without problems.