Some guidance for a remote sensor project

Hi all,

I currently have a Uno with an ethernet shield. I’d looking to use a remote sensor like this http://www.elecrow.com/devduino-sensor-node-v2-atmega-328-p-1046.html to report back to the Uno. Essentially I’d have the sensor send a report every hour, but I’d like the Uno to be able to also “request” and update for the current sensor values.
Few questions;

  • What module would be recommended for the RF component?
  • What sort of RF distance can be expected if just using a small extension wire as the antenna? (Need at Maximum approx 10 meters / 32ft)
  • Can the values from the sensors be transmitted to the Uno, if using Analogue inputs
  • I’d like to run some sought of framework on the Uno which would act as a server to collate/display the realtime sensor readings via a webpage (ajax/html5 ?). Also be able to have another PC query the Uno for its values, via jSON? Would be be recommended?

Thanks in advance!

  • What module would be recommended for the RF component?
  • What sort of RF distance can be expected if just using a small extension wire as the antenna?

It would be better if you specified the range you require, rather than effectively asking for a list of all possible radio transmission methods along with their range.

Thanks, edited my orig post.

Need at Maximum approx 10 meters / 32ft

for that range you have 2 options

NRF24L01 with external Antenna's would easily do that range, the NRF24L01's with on board antenna, are supposed to have 25m range, but personally I've found this rather optimistic

Simple 433Mhz OOK (ASK) transmitters and receivers also have that sort of range.

Both are well supported and are approximately the same price i.e a few dollars

I don't think for this sort of range you would need anything more complex e.g. like an XBee unless you have loads of transmitters

Analogue input data is converted to a digital number between 0 and 1023 which can be sent via either sort of transmitter

Thanks roger for the reply re the RF questions. Still unsure about choosing a framework and the best way to code using technologies, ajax, json, xml etc... ?

Cheers

I'd like to run some sought of framework on the Uno which would act as a server to collate/display the realtime sensor readings via a webpage (ajax/html5 ?). Also be able to have another PC query the Uno for its values, via jSON? Would be be recommended?

I didnt comment on this as I was unclear what you want to do.

You can connect Ethernet or Wifi to the Uno and there are examples of using the Uno as either a client or a server.

To run it as a server you'll almost certainly need some SD memory to store the web pages, (some ethernet shields come with this built in)

The issue would be whether you are accessing the server form inside your local network or are trying to access it remotely, and hence how you setup any internet router config to allow external access to the Uno's ethernet / wifi server

Alternatively (and often easier) is to just use the Uno as a client, and POST (HTTP POST / HTTP GET) (possibly using JSON etc) the data from the Uno onto a server on the internet e.g. running PHP or some other server side scripting language, and which also has a database to store the values.

Using an internet server (or a pc on your internal networking running for example WAMP), is going to give you the best suite of features.

As building nice looking complex web pages on the Uno is time consuming as there is no server side scripting, apart from using Print statements in the code.

But this is all highly dependent how you intend to consume the data.

Thanks, I'll probably do as suggested and simply POST the results to my web server to parse and save.

With those RF links, would they happily work using multiple "client" remote links all talking back to the Uno "server" Or would a xbee or similar be better suited?

Cheers

I don't think you need to use an XBee for this sort of simple application.

If you use the simple OOK transmitters and receivers, and use VirtualWire (or its new name RadioHead) apart from data collision issues, you can send whatever data you like, so there are not limits to the number of transmitters

If data collisions could be an issue (which I think is true in your case), then the NRF24L01 can (from what I recall) have 6 transmitters communicating with one receiver (but you'd need to check the details, as I've not done this myself)

Thanks, will do some investigation regarding the number of transmitters the NRF24L01 can handle.