Today we look at something practice-oriented again: Data Transmission using radio
or more precisely: wireless data transmission using microcontrollers like Arduino
If we talk about Arduino and wireless most of you probably will already think of
the ESP8266 or its successor ESP32, both using WiFi
So we speak "Internet": IP, TCP, HTTP or other related protocols
A big plus for the module: The small variants only cost about 2-3€ each
so not expensive at all. Another advantage: It's got an internal processor
so we actually do not need a separate Arduino to use the module.
And as said: It is Arduino-compatible and as such can be programmed using the well-known IDE
So it shouldn't be too hard to get started. You have however to think about APs.
You need an existing WiFi infrastructure. This can be both an advantage and a disadvantage
advantage: there are tons of ready-made devices available. There are APS
for various alignments, for inside and outside. There are repeaters, there are mesh-networks like Freifunk
So you have a lot of ways to access the network. But also not everywhere is WiFi available
What if you want to transmit somewhere without an existing WiFi Network?
There we could use something like this: A BC417 which uses
the same band but another protocol: Bluetooth. This one is cheap as well
the modules should be available for less than 5€. Also using them is pretty easy
because it's just a serial port which is looped through to the destination device
Also you get the whole bluetooth management including pairing with PIN
This ensures you get a point-to-point link with a reduced risk
of others interfering or intercepting the transmission. Also we can
connect to a smartphone and create own Apps to control our devic e.
The range is limited to about 100m in best-case-screnarios which might not
suffice for longer distances like deploying a sensor at the back of your garden
So we could just go totally overkill and use this guy: A SIM800L
This is using GSM, the classical mobile phone network.
Usually we also speak IP here an can just use the internet
but we also can use SMS, initiate and receive calls or use other cellular services.
Priceways the modules cost around 5 to 10€
Since we are using the mobile network we also get a basic security against interference and intercept
for controlling the module you can download ready-made libraries which should be easy to use
And since cell coverage is usually pretty good you can use your module nearly everywhere
Some people might argue GSM (1G/2G) is deprecated since we've already got 4G (LTE)
Some countries plan to shutdown 1g and 2G so only 3G (UMTS) and 4G (LTE) are left.
Over here in germany a lot of machine control equiptment is using GSM
also alarm systems and the federal-run toll-scanners mounted on highways largely use GSM-Modems
I for once do not think there will be a GSM-shutdown any time soon
There are just too many critical devices depending on it
A big disadvantage can be seen on the backside of the module
It needs a SIM-card and a associated contract, usually with monthly fees, to operate.
Also it's not easy to get a contract, because many carriers do not allow the use of their plans for automatic systems
Contracts and fees are not cool, so are there any alternatives?
Sure, for example this
This devices are somewhat new and called LoRa - Long Range or Low Data Rata - both kind of fit
This is an RFM98W based board. They use various bands
but sice I'm still learning the system I do not want to elaborate too much about this system
Pricewise a lot has changed in the last months
the modules - without adapter boards - used to cost 20€ and more, now you can get them for 6€ each
Advantage: You get a high range without local infrastructure
There are central gateways to transfer your data to the internet
this is however not widely deployed yet so if you plan to use this check coverage first
Also you see antenna connectors. Using suited antennas allows long distances
without using a internet gateway. I even saw a report about a guy getting a 60km link going.
OK, I guess you need corresponding mountains in your backyard for this
As said: watch out for availability - the modules can be hard to obtain
and if you do not want to build a receiver yourself, you need gateway coverage
To control the devices there should be libraries available.
Another important restriction is radio regulation
in Germany you are only allowed to use little airtime to not interfere with other users
Someone at the 33C3 calculated this would translate to about 20 measurements per day
For some sensors this might be sufficient but if you want to keep an eye at the outside temperature this might be to slow
and this module oversized
So can we get a bit less range and lower our costs further?
This should fit and you might have already seen this modules
There are various types with different names
In essence all of them are 433MHz radio modules
They are dirt-cheap, just a few cents for each PCB
But keep in mind those modules are really DIY
Its just a input, a bit of RF-voodoo and radio at the other end
You have to build your own antenna, so you should know how this works
But also other things required to transfer over radio, like Manchester Encoding, has to be implemented by yourself
Luckily there are some libraries taking away some of this work
But you still have to worry about receiving foreign data by accident
Because the used modulation is so common you'll receive anything other people with similar modules send
So you have to ensure in software you only receive data from your intended sender
Also note there are 2 PCBs - a transmitter and a dedicated receiver
So if you want to transmit and receive you have to attach both modules
Thats usually a good idea so you can return a note about correctly receiving the data
Also you're building radio equipment yourself, this might pose some legal questions
and cause disputes with nearby amateur radio operators
But if you've got a ham nearby you might just want to ask for help, the're usually happy to share their knowledge
As you can see there is some free space left, let's fill it up
This is a RF24 based module
this one was given to me by ICStation.com but as you can see - I got a box of similar modules already at hand
As you can see the've got a different style, but this is for another video coming up
The RF24 series are highly integrated radio modules
On the radio side they use simple modulations just like the 433MHZ-type
but they operate at 2.4GHz just like WiFi and Bluetooth
And this IC implements some intelligence by itself
You can create virtual pipes ensuring no one else accidentally introduces unwanted data
Also it uses checksums to ensure the transmission wasn't accidentally altered
So if you receive ABD instead of ABC due to flipped bits the module will detect this error
And there is an automatic retransmit, so if this module sends something the other one will answer "yes, I received everything without errors"
It there is no acknowledgment the sender will take another try and send the data again
So in every case you'll know if your partner received the transmission successfully or not
You see: Two modules, two styles so I can't make a lot of universal claims
The cheap ones should cost no more than 2 or 3€ max
More elaborate types like this one should be about 5€ to 10€
Also here you can use libraries to easily use the modules functions
So you just tell the library to send a text and as response it lets you know if everything worked or not
For the range it is hard to measure due to the different types of modules
The small variant has a PCB antenna just like the ESP 8266 or Bluetooth modules
For the larger module I soldered a antenna connector to it
And you can probably tell this WiFi-antenna will result in a better range than the PCB antenna
Its 2.4GHz so you can think of it like a very good WiFi system
So outside several hundered meters should be no problem, even for the small ones - if there are no harsh conditions
The large module got an additional amplifier so it can go even further
I think this should suffice as an overview of popular types to transmit data wirelessly using µCs like Arduino
For the RF24 i'll publish another video today showing its operation
And if you want to see details of any of the modules - well, except ESP8266, we got this extensively already
just post a comment below - LoRa is already on my list
bus as said: just comment if you want to see any of the other ones
With the exception of LoRa I used them all in the past and every module did as it is supposed to do
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