Best wireless transmitter for 30m distance through buildings?

Sorry if I am repeating an already frequently-sought question, but I searched google several times and could not find anything relevant to my project.

I want build a wireless mailbox mail detector for mymailbox which is located about 30 meters away from my house. In terms of line of sight, the signal has to pass through 3 houses. The sizes of the data being transferred is minimal and speed is not a priority. Most importantly, I would like to find the cheapest possible solution for this as I am on a very low budget. So basically something that will get the job done while keeping the price low. At the moment, I have no idea how much something like this would cost, so I dont have a budget. Any suggestions are appreciated. Thanks

Signal penetration depends on how the houses are constructed, but on such a low budget, the project is unlikely to succeed.

Okay. Well then whatever the cheapest possible option is.

The houses areconstructed out of wood if that helps somewhat.

I suspect the simplest relaible system is to use either the mobile phone system or the internet.

Otherwise you are faced with "suck-it-and-see". A pair of high power nRF24L01+ may work, and they are easy to interface to an Arduino.

...R

I was also thinking of nrf24L01, and I was wondering if there was any other similar board for the arduino that was more powerful? Things like the rfd900 (way too expensive), and ciseco XRF which is almost an exbee clone. Would xbees be powerful enough for the project?

I doubt that sheer power is able to penetrate a Faraday cage, but there a cheap high power modules with the nRF24L01+ and you will need a very solid 3.3 power supply using them.

1100-meter-long-distance-NRF24L01-PA-LNA-wireless-modules-with-antenna

I have used synapse rf100 or rf200 modules with very good results. Over a kilometer line of site. They were about 40 dollars a piece however and three houses is a lot of walls to go though!

http://www.futureelectronics.com/en/technologies/semiconductors/wireless-rf/rf-modules-solutions/802154-zigbee/Pages/6469811-RF200PD1.aspx?IM=0

Can you go around the houses, burying wire?

Consider a 915MHz RX/TX pair from eBay for a few dollars. The antenna for the TX can be a quarter wave stub coming out of the top of the mailbox. The box itself will make a good ground plane. Design it to transmit a coded message or a timed repetitive long carrier when mail is present. When not transmitting, the RX will get random trash data as the noise triggers the comparator. If the message is long enough and unique or the carrier is on for a distinct time then the RX will distinguish it from the trash data. You can use a Pro Mini and keep it in sleep mode and turned on when mail is detected. A beam break optical device might work as the mail detector.

Just some ideas.

a 915MHz RX/TX pair

Guaranteed not to pass through 3 wood frame houses.

Arctic_Eddie: Consider a 915MHz RX/TX pair from eBay for a few dollars. The antenna for the TX can be a quarter wave stub coming out of the top of the mailbox. The box itself will make a good ground plane. Design it to transmit a coded message or a timed repetitive long carrier when mail is present. When not transmitting, the RX will get random trash data as the noise triggers the comparator. If the message is long enough and unique or the carrier is on for a distinct time then the RX will distinguish it from the trash data. You can use a Pro Mini and keep it in sleep mode and turned on when mail is detected. A beam break optical device might work as the mail detector.

Just some ideas.

Thanks for the suggestions. I had a similar idea as well, to use an ir phototransistor and ir emitter to detect when there is a break in the beam. Unfortunately, there is no way to actually have the antenna outside the metal box as I have a community mail box (forgot to mention that that's another obstacle to the antenna range). Would you mind explaining how I could code the message or transmit a "repetitive long carrier"? Or is there a place on the forum or a thread that explains this? And how do you make the Arduino turn on when the ,ail is detected? I'm just completely new to the world of Arduino, and especially programming lol :o

jremington: Can you go around the houses, burying wire?

Unfortunately, that would not be possible. I would be trespassing city and private property.

Whandall: I doubt that sheer power is able to penetrate a Faraday cage, but there a cheap high power modules with the nRF24L01+ and you will need a very solid 3.3 power supply using them.

1100-meter-long-distance-NRF24L01-PA-LNA-wireless-modules-with-antenna

Ya I was also thinking that its worth a shot to see if those ones work. For the price, I can't go wrong. and even if they don't work, I can use them for other projects.

I have something like this up and running now, a attiny13 with a reed switch, and transmitting data with a nrf24l01 from inside a metal postbox,
My postbox is only 20 meters and 1 concrete wall away. not the few houses as in your case. I’m using one of the small ordinary nrf24l01 inside the postbox and a pa-lna version as receiver and that have worked fine for a year or so, you might need to use pa-lna version on booth sides thou.

If you get it to work have you thought abut how to show that you have mail?

Recently i updated my receiver side a bit,
now i have a nrf24l01 pa-lna connected to a esp8266 sending snail-mail notifications to my phone with pushbullet.
Nice to know if there is any point in taking a detour past the mailbox on the way home…

With any luck it might work for you too good luck.

You can penetrate wood structures with 915MHz as well as 903 and 1296. I've been doing it for many years as an amateur radio operator. If the TX is outside of a structure then you will get scatter from any surface boundary with a dielectric difference. If penetration is a concern then 2400 is not a good choice.

KF4JU