Smallest wireless module

Hello. I would like to build the smallest as possible wireless sensor to detect the presence or absence of a magnet and transmit it to a regular arduino connected on a PC. I would also like the longest energy autonomy.

So I have imaginated the following: -Arduino mini: sending that it is "alive" as soon as powered. -Reed sensor inverted. inserted in the battery circuit: allowing to power the arduino only when the magnet is away. -Emitter: http://www.lextronic.fr/P18741-module-hybride-emetteur-tx2s-433.html

Do you think it is a good idea? Or would you advice me to do it with another microcontroller than arduino, for example JENNIC ?

Thanks a lot for your advice.

Why do you need an Arduino to do the work of a reed relay or Hall-effect switch?

Can i just plug the reed sensor to the transmitter? Don't I need a microcontroller?

I really just need to know from my distant computer+ arduino wireless receiver if the magnet is removed... Maybe do you have a simpler solution?

OK I have just had a look at the transmitter and it has a DATA pin that can receive analogic or digital datas. So can i just plug the data pin to the VCC to set it to "1" And then use my reed switch to power it on or off?

The problem will be if I want to use several sensors and identify them.

The problem will be if I want to use several sensors and identify them.

You could use a 555 and a different tone for each one. Cheaper and lower power than an AVR.

I am going to have a look at 555 timers.

Do you agree with my previous post that a may not require a microcontroller? Just emitter + switch?
And the receptor plugged on my arduino-PC ?

Thanks again thousands of time

it has a DATA pin that can receive analogic or digital datas

My French isn't what it used to be, but I don't see that there is any reference to analogue input.

I don't really see that this application needs a microcontroller, but maybe there's something in your requirements that makes it necessary.

Economique et performant, il dispose d'une entrée "DATA" acceptant à la fois les données numériques (0 - 1) ainsi que les signaux analogiques.

This is the french sentence :-)

But compared to other on the internet this one seems expensive; and I also need the receiver. Do you know better devices?

Are the rec and transmitter coupled or can one receptor receive from several emitters?

This is the french sentence :-)

Ah ! Missed that one. Desolé.

I don't know about "expensive", I've bought similar from lprs.co.uk, and the pricing looks similar.

No, you can receive from any number of transmitters with one receiver. That's when the fun starts!

Merci mille fois AWOL !!!

I am going to compare price and length of reception.

If I have understood everything, All data entering the DATA pin of the emitter will be sent through the DATA pin of the receiver as if it was wired?

All data entering the DATA pin of the emitter will be sent through the DATA pin of the receiver as if it was wired?

Yes, but they work best if the input is changing regularly - long periods of DC input may not be received well (which is why, I think, Manchester encoding was mentioned).

Sorry, I'm not a radio expert.

AWOL:

All data entering the DATA pin of the emitter will be sent through the DATA pin of the receiver as if it was wired?

Yes, but they work best if the input is changing regularly - long periods of DC input may not be received well (which is why, I think, Manchester encoding was mentioned).

Sorry, I'm not a radio expert.

That's why i would like to place the Reed switch between the battery and the RF so as to allow it to be OFF without consuming energy most of the time and juste powered when the magnet is removed. This event will only happen once a day generally. Do you think it can be OK?

It may be OK, but it depends on how [u]expensive[/u] missing an event is, because, for example, someone happens to be pressing next door's wireless doorbell which just happens to be on the same 418/433 MHz band as your monitoring system, or someone is operating an electric drill, or... How long is the magnet present/not present? i.e, how long have you got to recognise and react to a valid signal?

Search the forum for "dirt cheap dumb wireless", DCDW, the kind of thing you are looking might be around already.

CrossRoads: Search the forum for "dirt cheap dumb wireless", DCDW, the kind of thing you are looking might be around already.

I will have a look at it. Would you recommend to use an XBee Rather than RF ?

Xbee is RF, just pricier RF. There are less expensive RF transmitters, such as te 434 MHz units from http://www.laipac.com/easy_434a_eng.htm The trick is - what data do you supply them with? If you had a minimal arduino (atmega chip, crystal, two 22 pf cap, 10K reset resistor, battery, you could wire up a pretty trimmed down arrangement to read the sensor and then transmit via Virtualwire with an address and some data checking built in so the receiver could tell when it received a good message.

CrossRoads: There are less expensive RF transmitters, such as te 434 MHz units from http://www.laipac.com/easy_434a_eng.htm The trick is - what data do you supply them with? If you had a minimal arduino (atmega chip, crystal, two 22 pf cap, 10K reset resistor, battery, you could wire up a pretty trimmed down arrangement to read the sensor and then transmit via Virtualwire with an address and some data checking built in so the receiver could tell when it received a good message.

The main problem is to have the smallest as possible.

Reading on Sparkfun: http://www.sparkfun.com/products/8946 "The theory of operation is very simple. What the transmitter 'sees' on its data pin is what the receiver outputs on its data pin". What kind of datas can be sent ?

So can I send recognisable data (ID for example) without a microcontroller?

Thus to simplify,i think i will try to set the DATA pin to "HIGH" by plugging it directly to VCC. Then if I plug the receiver to a Digital IO of my arduino, this IO will be set to HIGH too I guess.

That is too simplistic of a view. Say you and I were talking - well, say you were just listening with your eyes closed. Me and 5-6 friends are around, and you don't recognize our voices. Periodically one of just says "One".

Who said it?

"one",

"one",

"one","one",

"o"one", (messages overlapping)

What do you with those messages?

Thanks Crossroads for your very true illustration.

Nevertheless, in the first month only one sensor will be needed: can i nevertheless use this simple solution we have talked?? The french emitter whose link i gave this morning can send analogic datas. If I use different resistor to modulate the tension entering the data pin, can it be used to differentiate the emitters???

Then, for multiple sensors, as i was thinking in my first post, i need a microcontroller: I am not enough gifted and/or equipped in electronics to build my own circuit so i think i will have to choose between the following solutions: -arduino mini/nano + emitter + reed switch -XBee + reed switch

Okay, I went back and read thru the thread again.

Sure, you could do what you asked originally. After the circuit is powered up and transmits your message (and you could have it send a couple of bytes, say its unique address for instance, send it 3 times 1/2 second apart or something to make sure the receiver sees one of them) then go into power down sleep mode until the reed switch kills the power, and turns it back on at a later time. Virtualwire will ensure that there are enough bytes sent for the receiver to sense that a message is being sent, get in sync with it, and come away with a usable transfer.