Communicate (one-way) with simple sensors wirelessly.

I were surfing web in order to find answers and looks like still have to pick up on knowledge in order to efficiently search for what I trying to accomplish.

Task: Arduino (or similar) host that processes data have to communicate (at least receive) data with simple sensor Hall Effect Sensor. We've got 6 doors/windows so 6 sensors should be in place. I am looking for most efficient way to wirelessly send data out of sensors (using RF transmitters?) to Arduino board. Only thing, is that I don't want to have extra Arduino board per each sensor. What is the best way to get data out of sensors?

If there is any RF bounce technique, to sort of send signal and get response back? Or there is way to build simple filter of Hall sensor that will pop additional header (id, checksum) to packet and send through RF transmitter? Those sensors should be very low powered, potentially powered by simple battery or solar (with ability to store some power and with optional transmitting data about available power).

If there is ways to avoid using Arduino for this sensor + transmitter? As you understand is topic of home security. Am I going too far from the beginning? (I'm developer, but haven't tried physical yet). What would be action plan here? I am noob, and need at least some terms and directions (don't give me fish, give me rod ;) ).

I don't think it is possible to get data from a sensor wirelessly without adding some form of transmitter to the sensor, and I guess infrared transmission is probably the cheapest, but has obvious limitations - such as not penetrating walls.

What sort of budget have you in mind?

Could you wire a few sensors to a single transmitter to reduce the number of transmitters?

Why not just wire the sensors?

...R

Budget is flexible (not a problem). I just think of elegant solution rather than 'just works'.

In order to use transmitter some controller chip is needed, right? What if Hall Sensor would directly somehow output analogue value into Transmitter that would send data to host? Is that possible?

There is option to apply 2 extra Arduino Mini (smallest?) boards per two sensors and transmit from them to host. But Idea is to avoid unnecessary full boards.

Reason of not wiring them, as I don't want to have wires all around the house :D

You don't need to use a full-fledged Arduino, or even a big Atmega 328P at each sensor. I would use an ATTiny for each sensor.

I would be possible to send an unencoded RF pulse to a circuit which would then echo the pulse back or not depending on the state of the sensor. But unless you used a different RF frequency for each sensor, the lack of ID code means you can't tell which sensor is which. An ATTiny is the easiest way I can think of to implement ID codes so sensors can share the same RF frequency.

EDIT: No, I take that back. You could identify sensors by the length of the reflected pulse. Would require a bunch of components (such as RC delay circuits) though, possibly to the point of being more complex than an ATTiny.

How will you provide power to the sensors? If battery, how long does it need to operate without changing the battery?

Not 100% sure about them, but I think these sorts of devices are set up for switch closures:

http://www.ebay.com/itm/433Mhz-RF-Transmitter-Module-and-Receiver-Link-Kit-for-Arduino-ARM-MCU-WL/221263133285?rt=nc&_trksid=p2047675.m1851&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D261%26meid%3D704519192167502844%26pid%3D100005%26prg%3D1088%26rk%3D3%26rkt%3D5%26sd%3D251320232941%26

They also exist in 315mHz varations.

Not sure, either, how you distinguish one from the other when several are operating. Maybe add a 555 timer and send different pulse widths, counts, etc. for each one.

You might consider using a Moteino http://lowpowerlab.com/moteino/ which is a small board with an Arduino and a wireless transceiver. I haven't used (or even seen) a Moteino but I am using DelTinos http://www.deltino.com/ which are a good deal more expensive because they are VERY small.

...R

Why do you want to use hall effect sensors. This makes the design of the entire transmitting arrangement difficult because you have to deal with analog voltages. If you used reed switches which are just open or closed, its a lot easier. You could then use reed switch > SC2262 encoder > cheap 433 Mhz transmitter.

JohnHoward:
Not 100% sure about them, but I think these sorts of devices are set up for switch closures:

http://www.ebay.com/itm/433Mhz-RF-Transmitter-Module-and-Receiver-Link-Kit-for-Arduino-ARM-MCU-WL/221263133285?rt=nc&_trksid=p2047675.m1851&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D261%26meid%3D704519192167502844%26pid%3D100005%26prg%3D1088%26rk%3D3%26rkt%3D5%26sd%3D251320232941%26

They also exist in 315mHz varations.

Not sure, either, how you distinguish one from the other when several are operating. Maybe add a 555 timer and send different pulse widths, counts, etc. for each one.

The VirtualWire library that works with these and is also compatible with the ATTiny85. I can’t imagine a more inexpensive method.

I would think that the building layout would be a strong determining factor (distance, size, number of floors, materials, commercial, residental). Six doors and six Windows? Do they have anything in common? single floor, common hallway, common attic, common cellar ? For example if there was a common cellar (or attic) then: reed switched, battery and IR led on each location. Place the LED in the cellar along with a single IR sensor to the arduino. You would need something to create a unique signal for each location

I am building something similar using attiny85 (and attiny84 for when i need more pins), an nRF24L01 from ebay http://www.ebay.com/sch/i.html?_odkw=nrf2401%2B&_sop=15&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.XNRF24L01%2B+&_nkw=NRF24L01%2B+&_sacat=0 with a 3.3v battery.

The main hub has ethernet shield (as well as the RF module), so i can get and send data to my home network.

Hope this helps.

These low cost transmitters work really well with an ATtiny85 using VirtualWire.

I tried the NRF24L01, but it needed more pins than I wanted to use.