Need guidance on mailbox notifier project - Page 1
Forum section: electronics / beginners

author: John0922
author_rank: Contributor
timestamp: September 05, 2017, 06:29:55 pm
content: Hi- I'm new to electronics but have some experience with Arduino. I'm looking to build a simple transmitter / receiver to notify me when my mail has arrived. The mailbox is about 2000 feet away from my house, with other houses blocking the line of sight. The mailbox is one in a bank of boxes, serving my entire street.My initial idea was to use a photo-resistor, since the box sits dark most of the time and light floods in when the mailbox panel is opened. Ideally, not much power would be drawn while the mailbox is dark. Since I don't want to freak out the mail carrier, I was thinking of putting the whole thing in a padded envelope addressed to me that I could just place in the box on the days I want to be notified.I've Googled some transmitter / receiver pairs for the Arduino and the HC-12 seems like a possibility, although it has more capability than I need, since I don't need to do serial communication. Also, I'm not sure if its range is quite enough, and it uses 5 volts.There's one on Sparkfun (RFM22B) that lists its range as 600 meters but I'm wondering if that will be quite enough.As you can probably tell, I'm inexperienced so any guidance insofar as what to get and how to set it up would be greatly appreciated.Thanks, John

author: John0922
author_rank: Contributor
timestamp: September 06, 2017, 02:36:48 am
content: I just found out the distance from the mailbox to home is more like 600 feet.If someone could recommend a transmitter / receiver pair, I could probably figure out the rest.Thanks again.

author: Beamin
author_rank: Super Contributor
timestamp: September 06, 2017, 04:34:54 am
content: Hey maybe this can be our group project? I have been looking to build something like this for a while and I can tell you what didn't work.455mhz chip used for key fobs can be bought for a few dollars and you just supply crystal ant signal and power. They can be bought in pairs off digikey.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: September 06, 2017, 05:13:12 am
content: Quote from: John0922 on September 05, 2017, 06:29:55 pmIf your mailbox is the common type that I have seen, the mail person opens the entire back panel revealing all of the pigeon hole boxes for easier access. It would be time consuming and clunky to open every box that gets mail from the front, therefore, your mailbox will get open anytime mail is placed in any of the boxes.Also, I don't know where you are from, but in the US, it is a federal offense to tamper with mail or mailboxes. Someone from Homeland Security or the FBI will be knocking at your door.

author: BrianHG
author_rank: Super Contributor
timestamp: September 06, 2017, 05:21:57 am
content: You can cheat and use one of these 433Mhz transmitters with a 1km range:https://www.alibaba.com/product-detail/High-sensitivity-Long-Distance-High-Power_1975395598.html?spm=a2700.details.maylikehoz.17.697a8c3eFLI3gJOr, with 3km range: (You wont have trouble with this one, except maybe with the FCC)https://www.alibaba.com/product-detail/universal-3km-433-mhz-transmitter-KL3000A-_1851002652.html?spm=a2700.details.maylikever.16.697a8c3essJBlUNote they need 9-12v, plus your data modulated signal.Units exist with an encoder on them and you can buy a dumb receiver unit, or, a receiver with a decoder on it with relays to switch on your bell or alarm...3km with encoder:https://www.alibaba.com/product-detail/315-433Mhz-3000m-Long-Range-Wireless_60216166475.html?spm=a2700.details.maylikever.10.697a8c3enjlB7wI know they look like cheap junk, but I purchased the top 2 and they work through a few houses, up to 2 blocks away clean.If you have a public outdoor shared multi mail box at the corner of your street for all the houses on the block, it may be illegal to leave anything in there or make any modifications.(Little cheating hack if the above paragraph pertains to you) Mail yourself a box containing you transmitter device, battery powered, which can sense mail going into the box, and transmit. When you get this package in the mail, never remove it from the mail box... But, the battery better last through the year with temperature changes and the sensor which tells it new letters have been added from the rear...

author: Beamin
author_rank: Super Contributor
timestamp: September 06, 2017, 05:00:50 pm
content: Quote from: tpowell1830 on September 06, 2017, 05:13:12 amDon't mess with the post master general!!!! He said 2000 feet which is normal in rural areas. These are just single mail boxes where its a box with a door on front. No keys no separate entrance exit doors. I don't think they enforce this law for residential mail boxes. My friend used to run mine over with the car when I was a kid for fun. So one day I put a concrete post in the middle and told my friends not to run it over. A green puddle sat next to the mail box the next day.

author: John0922
author_rank: Contributor
timestamp: September 06, 2017, 07:37:46 pm
content: Quote from: BrianHG on September 06, 2017, 05:21:57 amHi Brian- Thanks, these seem to be exactly what I'm looking for. But I'm a little confused by the Alibaba site. Is there a way to buy just one of these?

author: dr.diesel
author_rank: Super Contributor
timestamp: September 06, 2017, 07:43:06 pm
content: Nothing like a circuit board, misc wiring and a sensor or two taped to the inside of the Postbox to send the worker postal.You'll have the bomb squad there in no time!

author: GreyWoolfe
author_rank: Unknown
timestamp: September 06, 2017, 07:50:59 pm
content: Quote from: blueskull on September 06, 2017, 04:59:01 amI have a ham radio friend that lives in a subdivision that are all multi acre lots. He has to drive 1.7 miles to the mailboxes, some of it on dirt roads. He is not rural, just a really big subdivision with large lots. I thought he was joking until I went to his house to pick some stuff up. He said that the building I passed when I came into the subdivision was where he went to get his mail.

author: John0922
author_rank: Contributor
timestamp: September 06, 2017, 07:54:45 pm
content: Quote from: dr.diesel on September 06, 2017, 07:43:06 pmHi Dr.- The plan is to put it all in a padded envelope and just put it in the box for the weekends. I haven't worked out all the details yet.

author: edavid
author_rank: Super Contributor
timestamp: September 06, 2017, 08:18:29 pm
content: There are a number of commercial units of this type:https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=wireless+mail+alert&rh=i%3Aaps%2Ck%3Awireless+mail+alertThey usually use a tilt switch sensor, or a magnet and reed switch. Either one is more practical than an optical system.Any experienced mail carrier will have seen one before, so you don't need to mess around trying to disguise what you are doing. (I think that is much more likely to perturb the carrier.)The biggest problem you'll run into is transmitting RF from inside a metal box. For my standalone mailbox, I ran an antenna wire down the post, but I doubt you have that option.

author: John0922
author_rank: Contributor
timestamp: September 06, 2017, 09:50:23 pm
content: Quote from: edavid on September 06, 2017, 08:18:29 pmI'm hoping to make use of the fact that the door of the mailbox is open when transmission takes place. Do you think that will help?

author: BrianHG
author_rank: Super Contributor
timestamp: September 07, 2017, 05:37:43 am
content: We are at a point where photos of your mail box might help us help you...

author: John0922
author_rank: Contributor
timestamp: September 07, 2017, 11:11:23 pm
content: Quote from: BrianHG on September 07, 2017, 05:37:43 amIt looks like this. The mail carrier opens it from the front. Thanks.

author: Brumby
author_rank: Unknown
timestamp: September 08, 2017, 05:56:21 am
content: That looks all-metal. If so, unless the opened side of the mailbox is aimeddirectlyat your receiver, I think you are going to have major problems transmitting from inside the box. Even then, there are going to be challenges.I'd be inclined to build a box and mount it to the panel the postie opens - if at all possible. That way, it would be exposed to the open air - and (hopefully) would not have the panel between it and your house. (Big crossed fingers here)Activation by a lever type micro switch. I'd also suggest mounting via a bracket that would allow you to access the box from your own door at the front for maintenance and battery changes..... just some ideas.

author: John0922
author_rank: Contributor
timestamp: September 08, 2017, 09:19:12 pm
content: Thanks to all who responded. I'm starting to think the challenges can't be overcome, but I picked up a pair of nRF24L01 w power amplifier and I'm going to do some experimenting.

author: Beamin
author_rank: Super Contributor
timestamp: September 09, 2017, 06:13:29 pm
content: Quote from: dr.diesel on September 06, 2017, 07:43:06 pmI was totally thinking about the unabomber when I read that he wanted to put fake mail it that contained electronic parts. Seriously don't do this. The authorities do take this stuff seriously; I had a friend that made a joke once and was investigated. It wasn't something he will do again. Even if you are innocent and didn't mean any harm its not treated that way and will be at least a huge amount of stress.

author: Beamin
author_rank: Super Contributor
timestamp: September 09, 2017, 06:47:44 pm
content: Quote from: John0922 on September 06, 2017, 07:37:46 pmI was wondering that myself. I especially like how you could experiment with your own antenna set up like a directional yagi.I sent the supplier a message asking if they could send a sample and how much it will cost and also asked if they had matching receivers. I put down that I wanted to buy 3000 units so maybe I will get a free one or five if so I could send you one. I remember back in the day you could just call companies and they would just send you free samples. Not sure if the world still works like that with the internet being what it is.

author: BrianHG
author_rank: Super Contributor
timestamp: September 10, 2017, 07:16:18 am
content: Quote from: Beamin on September 09, 2017, 06:47:44 pmSee my tested ranges of the 1km and 3km units in an small city/urban area:Consider the Green Circle a safe bet if your transmitting antenna is at ground level for the 3KM unit. If you are out of the city, think closer to the white circle. To get this range, I had the transmitter on the second level of my house, though my house was is a vertical depression, so you might call this ground level while the tested circles were measured with a battery powered receiver I walked around with...The red arrows illustrated the number of brick walls the signal had to penetrate to get to my receiver.The blue circle is the 1km transmitter.I requested a quote for 5 from this guy: (Even though he says 200pcs minimum, he still sold me 5, + 5 receivers)TXhttps://www.alibaba.com/product-detail/universal-3km-433-cheap-rf-module_1809987082.html?spm=a2700.7724838.0.0.r8Q13YRXhttps://www.alibaba.com/product-detail/315-433MHZ-RF-ASK-Receiver-Transmitter_2005979852.html?spm=a2700.details.maylikever.10.697a8c3epkWsf4

author: BrianHG
author_rank: Super Contributor
timestamp: September 10, 2017, 07:34:29 am
content: If you want the expensive sophisticate route where you need to build a PCB with a printed antenna, program a MCU with data radio, consume more power, here is the cheapest LoRa(TM) module I've seen. I cannot confirm the distances since I never used one. You will need 2, one at each end...https://www.digikey.ca/product-detail/en/microchip-technology/RN2903A-I-RM098/RN2903A-I-RM098-ND/6823704