would like some suggestions

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Hi,

I'd like to make a 'mail alert ' rf system ( for snailmail). My mailbox is 250+ ft from the house, and on cold days I don't like to venture up there until I have to. On the other hand, I prefer to do it during (the few) daylight hours we have in the winter.

 

Has become more of a problem lately.  Mail used to get here between 3:30 and 4. So, it worked out OK. Now it sometimes doesn't show up until almost 6, and of course there are the days when we're not blessed with catalogs and bills.

 

In any event, I just want some kind of small transmitter that will transmit a one time short burst when the mailbox door is opened. Several issues come to mind

 1. The door 'switch' needs to be a little tolerant, in case the door doesn't get fully closed -- mercury switches come to mind, but they are probably frowned upon these days.

 2. I have no idea what would be a reliable ( and cheap) rf system. I will gladly do the investigation, but I'd like some direction.

  - I've worked  with RF, but I'm hoping for 'modules' or at least a cookbook design.

3. Low power -- I'm thinking lithium batteries due to the temperature range. Ideally, it should just power up when the door is opened and auto shut off after. I have some ideas about that, but any thoughts are appreciated.

 

Thanks,

 

hj

 

ps -- we're probably 500 feet from the nearest neighbor, so rf conflicts are probably not an issue.

 

 

 

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You can use BLE to get the range.  I have a kit here from 'Another" vendor that can easily do it, and run on a CR2032 coin cell for a couple of years based on Trigger>send message>sleep.

 

Not sure if Mchip, or Atmel have anything that can do this.  But be patient, I know a freak that will probably answer this shortly wink

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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I have used remotes from rf controlled outlets. 

And then you don't need to do any programming a switch that make it send a "key" while open.

If the lamp is on you have mail :)

 

Perhaps a remote outdoor  temperature sensor where you short the sensor when it opens, and stay short, then you "rearm" it when you pick the mail up.

 

perhaps a laser beam while open, into a window where there is a sensor 

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Laser (or any optical) won't work in snow or fog.

 

Probably over-kill for LoRa.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Something like this perhaps?   https://www.amazon.com/Mail-Chim...

 

Or would you prefer email / text alert  https://www.amazon.com/MAILBOX-E...

 

Jim

Last Edited: Wed. Jan 17, 2018 - 09:46 PM
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About 80m no problem!

It's not a high speed system, just a on signal for about ? 20 sec

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Use a good battery at the remote end, most types do not like cold wx.

 

Jim

 

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Vandalize a radio-controlled door bell? Break into transmitter and replace push.button with an external switch (a micro-switch perhaps?) with relatively long travel.

 

I had a look at my local gadget shops website, and they had one with 100 meter range @ SEK 100 (which is something like $9 or $10).

 

Is the mailbox visible from the house? Perhaps instead have a solution local to the mailbox - a flashing LED indicating the box has been opened? I thought you 'Mercans had those cool mailboxes with a flag/semaphore being raised when the mailbox is opened..?

As of January 15, 2018, Site fix-up work has begun! Now do your part and report any bugs or deficiencies here

No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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Jim already mentioned BLE, (the new and improved Bluetooth).

 

XBee also comes to mind, with a range of RF power options available.

 

WiFi would be another option, ESP8266 modules only cost a couple a bucks these days.

 

If your mailbox is metal, then remember you want an RF module with the ability to attach an external antenna, or mount the electronics in a plastic box on the post, and run wires to the mailbox's switch.

Having the RF module inside a metal mailbox won't work.

 

Another option for the mailbox door sensor would be a reed switch and a magnet, or you could get fancy and put an accelerometer (tilt) sensor on the door.

 

If your RF module has a stand-by input signal, that's great.  Otherwise I'd suggest an NFet driving a PFet as a High Side Switch for turning the RF module on and off.

Have a look at the DMC2038LVT as an example, others certainly exist.

 

You could, of course, just ask the mailman to toot his horn when he delivers mail to your residence...

 

JC

 

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I thought you 'Mercans had those cool mailboxes with a flag/semaphore being raised when the mailbox is opened..?

 

Most residential mailboxes do have a red flag that can be raised or lowered.

 

The flag, however, is to indicate to the mailman that the resident has placed a letter in the box for the mailman to pickup, i.e. outgoing mail.

That way the resident doesn't have to venture out to mail the letter.

It isn't used by the mailman to indicate the presence of incoming mail.

 

JC 

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sparrow2 wrote:
I have used remotes from rf controlled outlets.
or a RF keyfob remote.

RF Digital's RFDP8 has excellent outdoor range on CR2032 (IIRC) but at 2.4GHz (greatly attenuated through walls)

RFDP8 has an ad hoc network mode (mesh network for increasing range)

The always-on receiver module would consume 17mA typ so could be powered from AA nickel cells.

If can get the 2.4GHz carrier to the interior doorbell ringer then there's separated extra low voltage AC to charge the battery or power the receiver with another ring tone for the postman.  

Keyfob would need some hardening to keep the CR2032 dry.

A continuously open mailbox door would drain the CR2032. (momentary switch)

 

RF Digital

RFDP8

1 Button Keyfob Remote

http://www.rfdigital.com/product/rfd21733-rfdp8-rf-module-2/index.html

https://www.mouser.com/RF-Digital-Wireless/Embedded-Solutions/RF-Wireless-Modules/RF-Modules/_/N-6sri4?P=1yzihkk

 

Edits: Mouser, 17mA

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Thu. Jan 18, 2018 - 04:06 AM
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Smoke signal, but you have to first sort the incoming invoices from the rest and provide the source of ignition.

 

Ross McKenzie ValuSoft Melbourne Australia

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jgmdesign wrote:
Not sure if Mchip, or Atmel have anything that can do this. [BLE]
Microchip does have BLE (Bluetooth 4, coin cell) modules and Bluetooth 2.1 modules (RN41, RN42) though these are iffy for coin cell.

RN42 is low power; its range might make 80m with a whip antenna.

RN41 is higher power and can reach 80m as is but it's 2.5mA typ deep sleep.

 

Microchip

RN42

http://www.microchip.com/wwwproducts/en/RN42

Microchip

RN41

http://www.microchip.com/wwwproducts/en/RN41

via several hops from

GitHub

https://github.com/jeffboody/spp-mirror

This project combined with Linux-on-Android can enable a complete Arduino development environment on Android.

...

 

https://github.com/jeffboody/spp-mirror#about

...

To work around these issues this app runs as a service which connects to Arduino over Bluetooth and to the avrdude programmer over a TCP socket. The serial and TCP data are mirrored by the Serial Mirror app. As a result the Serial Mirror app is also useful for devices which do not have root access. After starting the Serial Mirror app you can connect via a telnet app to send and receive data from the Bluetooth device. 

...

The Bluesmirf Bluetooth module is available from Sparkfun.

The Serial Mirror is available on the Play Store.

...

Linux on Android – Brining (GNU) Linux to your Android device

http://linuxonandroid.com/

 

"Dare to be naïve." - Buckminster Fuller

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 Magnet, reed switch and wire. 250 ft of wire to be run in a trench would cost you some money but this is the only do-and-forget solution. The wire can also be used to power a lamp above your mailbox.

 High frequency RF may or may not be able to cover > 80 m between your house and mailbox. It will depend on the obstacles: trees and bushes, poles, power lines. I would start with 433 MHz. I guess this band is not licensed in your location.

 I would not worry about Tx energy consumption of mailbox part too much because transmission will happen once a day and take < 1 s. You'll have to have your mailbox device physically turned off all the time. Only opening mailbox door should power on transmitter. When turned on, transmitter sends a couple of bytes and goes to power-down mode. When mailbox door is securely closed, battery should be disconnected. Thus, battery's self-discharge and chip's consumption in power-down mode are the most important parameters. The former is especially important because of low ambient temperature.

 Data sent from mailbox sensor will contain a preamble, device signature to distinguish your mailbox from the other RF devices you have indoors, payload and checksum. Payload may contain battery level. In order to measure battery voltage you'll probably need a step-up DC converter.
 

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DocJC wrote:
The flag, however, is to indicate to the mailman that the resident has placed a letter in the box for the mailman to pickup, i.e. outgoing mail. That way the resident doesn't have to venture out to mail the letter. It isn't used by the mailman to indicate the presence of incoming mail.

I never knew that - So the flag is essentially a "Request To Send" flag and the OP needs either a "Ring Indicate" or "Delivered iTems Ready".

 

Why not simply fit a second flag ? Or would training the postman postperson be too difficult.

 

Aah! So regarding the mailbox flag in "The Lake House",  It's operation was quite normal and wasn't being abused at all because I don't remember the postman making an appearance.

 

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You can put a string on your letterbox and run it to a bell in you house.

LoRa modules should have no trouble in bridging the gap to your house.

But all electronics need a power source.

A lithium battery of size 18650 should have plenty of enery to keep your mailbox going for 10 year or so.

But I don't know about self discharge rates of rechargable lithium (-ion / other) cells).

 

You could add a solar cell but that will need extra weather and hufter proofing.

A super capacitor (2V7 100F USD3) is probably also enough tho bridge a few dark days if you combine it with a solar cell.

 

Have a look at jeelabs. He has done some extensive blogging of low power AVR's with RF communication modules.

 

----------------------------

You can also put your mailbox on top of something like this:

https://www.aliexpress.com/item/...?

With a bit of programming you should be able to make it smart enough to drive to your front door if it has received mail.

 

----------------------------

Or get a bigger mail box.

Then you only have to empty it once a week.

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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THIS looks like a perfect solution:

 

https://www.amazon.com/Bluetooth...

 

It communicates to an app on your phone.  

 

Some more information:

http://www.blehome.com/contactse...

 

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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Paulvdh wrote:
A lithium battery of size 18650 should have plenty of enery

Li batteies do not like cold wx!

 

Jim

 

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Yabusame wrote:
The wire can also be used to power a lamp above your mailbox.
Could be wireless.

Primary and secondary school zones here have a battery powered automobile traffic caution light that's PV recharged with a Yagi pointing at the school district service yard (maintenance, school bus depot, food and nutrition management)

Yabusame wrote:
I would start with 433 MHz. I guess this band is not licensed in your location.
USA FCC first ISM is approximately 900MHz.

Yabusame wrote:
In order to measure battery voltage you'll probably need a step-up DC converter.
Another use for a SMPS is the CCS for an LED light in lieu of "lamp above your mailbox".

 


AFAR Communications

FCC Rules for Unlicensed Wireless Equipment operating in the ISM bands

http://afar.net/tutorials/fcc-rules/

Mouser Electronics

Bench Talk

THAT Doesn’t Need Circuit Protection!

On February 11, 2014 in Circuit Protection by Kelly Casey (VP of Engineering for FM Technical Consulting)

https://www.mouser.com/blog/that-doesnt-need-circuit-protection

Photovoltaic cells recharge nickel cells that power an LED walkway light

 ...

(BOM)

2 x AAA Rechargeable Cells (not pictured)

3 x Solar Cells (not pictured)

(etc)

...

"Dare to be naïve." - Buckminster Fuller

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The thread title could be more informative!

 

I'd say this is a bit far for BLE 4 - you would certainly need (very) good antennas, and clear line-of-sight.

 

I would doubt that PCB or chip antennas would suffice.

 

BLE 5 offers "range extensions" ...

 

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ki0bk wrote:
Li batteies do not like cold wx!

Lets face it ... No batteries like the cold, but lithium–thionyl chloride primary cell types stand up well enough to be useful at even -40° and at one short RF transmission / day will easily last 10 yr.

 

Here's an example:

https://uk.rs-online.com/web/p/a...

 

Last Edited: Thu. Jan 18, 2018 - 02:50 PM
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Yabusame wrote:
In order to measure battery voltage you'll probably need a step-up DC converter.

Eh??

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Paulvdh wrote:
But I don't know about self discharge rates of rechargable lithium (-ion / other) cells).
Those are low self-discharge (LSD) and the LSD NiMH are even less (IIRC a few micro-amp)

Paulvdh wrote:
Or get a bigger mail box.

Then you only have to empty it once a week.

That can be handy for when one forgets to send the hold mail delivery postcard to the local post office (I made that mistake once before a long road trip)

 


PowerStream Power supplies, battery chargers, batteries and packs, dc/dc converters, injection molding

The world's first round lithium polymer battery from PowerStream

https://www.powerstream.com/round-li-polymer.htm

...

4. Self-discharge is less than 1% per month 
...

 

"Dare to be naïve." - Buckminster Fuller

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I have used BLE121LR and they will work with no problems at 100m (don't trust the up to 450m)  

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Some Li primary cells can exceed the industrial temperature range.

http://www.tadiranbat.com/compare-lithium-cells.html

 

Can recall only one Li secondary cell that can be recharged at 20mA for AA at less than -20C :

Tadiran Batteries

Product Spec Sheets

http://www.tadiranbat.com/product-spec-sheets.html

(bottom)

TLI Series (Rechargable)

 

"Dare to be naïve." - Buckminster Fuller

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sparrow2 wrote:
I have used BLE121LR and they will work with no problems at 100m (don't trust the up to 450m) 

You mean this:

 

SiLabs wrote:

Bluegiga BLE121LR Bluetooth® Smart Long Range Module

World's Longest Range Bluetooth Smart Module

BLE121LR is a Bluetooth Smart Long Range module targeted for Bluetooth Smart applications where the best possible RF performance and range are required. At +8 dBm TX power and -98 dBm sensitivity BLE121LR has best-in-class RF performance and can provide Bluetooth Smart connectivity up to 450 meters. 

 

https://www.silabs.com/products/...

 

Probably a bit risky recommending competitor products here - as both Microchip & Atmel have/had BLE (and other RF link) products ...

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awneil wrote:
BLE 5 offers "range extensions" ...
Bluetooth 5 modules are new arrivals at Mouser; 2 of 4 :

https://www.mouser.com/new/laird/laird-sable-x-r2-bluetooth-5/

https://www.mouser.com/new/rigado/rigado-bmd-330-modules/

 

"Dare to be naïve." - Buckminster Fuller

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The USPS here has a free feature called "informed delivery". I get emails, with pictures of my mail.

It all starts with a mental vision.

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awneil wrote:

Yabusame wrote:
In order to measure battery voltage you'll probably need a step-up DC converter.

Eh??

 

 Reference voltage. And we need it higher than Vbat, otherwise ADC will always return 0x03FF, or whatever its resolution is. No?

 

 

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Two resistors make a voltage divider that can knock batt down

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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but beware that a voltage divider constantly across the battery will add to the drain ...

 

 

EDIT

 

Also - especially with lithium batteries - measuring the terminal voltage probably doesn't give much useful information ...

Last Edited: Fri. Jan 19, 2018 - 12:18 PM
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awneil wrote:
but beware that a voltage divider constantly across the battery will add to the drain ...

Agreed, the point I was making is that you absolutely do not need a Step up converter.  For the resistor divider, one could put one end to Vbatt, the other to an unused I/O pin on the micro and activate it by pulling the I/O pin low.  When not needed drive the line high, or set it as an input

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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jgmdesign wrote:
the point I was making is that you absolutely do not need a Step up converter.

Absolutely.

 

 

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About measuring battery voltage:

1). Use a battery chemsitry that is compatible with your uC. 2 AA's will do (Are alkaline's low temp resistant?)

2). Use Vcc as the ADC reference.

3). Measure the internal reference voltage with the ADC. No external components needed.

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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Paulvdh wrote:
(Are alkaline's low temp resistant?)
No

An alternative to OTC alkaline is lithium iron disulfide which is also OTC with an impressive low temperature performance.

If can move to nickel metal hydride then eneloop is one model that's good to -20C (maybe more if greatly reduce the load)

 

http://data.energizer.com/pdfs/l92.pdf (AAA, Li/FeS2)

via http://data.energizer.com/products.aspx (Chemistry pull-down menu, Lithium Cylindrical)

Energizer

Cylindrical Primary Lithium

Handbook and Application Manual

http://data.energizer.com/pdfs/lithiuml91l92_appman.pdf

(page 4)

Temperature Effects on Performance: 

...

Batteryspace.com

NiMH Rechargeable Cell: Panasonic Eneloop AAA 1.2V 800mAh (4 pcs/pack)

http://www.batteryspace.com/nimhrechargeablecellsanyoeneloopaaa12v800mah4pcs---immediatelyusable-2.aspx

...

  • Work in extreme temperatures down to -4° F (-20ºC)

...

 

Edit: typo

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Fri. Jan 19, 2018 - 06:29 PM
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Something like this perhaps?   https://www.amazon.com/Mail-Chim...

That looks like it might do the trick -- Thanks Jim

 

Never dreamt that there were regular products for this application.

 

Thanks for all of the other thoughts as well.

 

hj

 

ps - my remote thermometers always say to use lithium below -4F. Alkalines definitely suffer at those temps. We usually have a few -15 to -20 temps every year.

 

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The device looks prety good -- except...

 

It's powered by an A23 battery (12v) which seems to be available in alkaline, alkaline, or alkaline...

 

Everything I've read says that alkaline batts start to fall apart pretty badly at -4F(-20 C). We typically get a few nights of -15 to - 20 (F) -- one year the high on one day was -5F.

(why do I live here ? keeps out the riff raff :) )

 

Looks like I can get some Panasonic 3V BVR series lithiums with thru hole posts. Could probably hook them up to a small 'breadboard PCB' and use that in the winter. Not sure how to do a good job of connecting it to the device battery contacts.

 

Open to suggestions -- and thanks for all the help so far.

 

hj

 

 

 

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Verify that the device itself will work at and below -4F(-20 C).

 

 

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Also determine the min charging temperature.  For my LiFePO4 house bank it is 5C.

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This is cool - I don't care who you are ;) Thanks Jim

You may only be one person in the world but, you may be the world to one person! "Life! Life, do you hear me? Give my creation LIFE!" Gene Wilder SKYPE Name: JonRobrt

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KitCarlson wrote:
The USPS here has a free feature called "informed delivery". I get emails, with pictures of my mail.
This is by far the best option, though you do not get to build or buy anything.

 

https://informeddelivery.usps.com/box/pages/intro/start.action

 

 

 

"void transmigratus(void) {transmigratus();} // recursio infinitus" - larryvc

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"Make XMEGA Great Again!"  - Greg Muth

Last Edited: Tue. Jan 23, 2018 - 01:13 AM
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The informed delivery and web cams, greatly simplify my complex life of living between two distant locations.

It all starts with a mental vision.

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Just had an epiphany (or a brain fart, I'll let you decide).

 

If you want to play a bit with linux you can use a system such as a raspberry pi or beaglebone with a webcam and openCV for image recognition.

Then you don't need a RF system, but you can mount the webcam in line of sight from your mailbox.

 

But be warned.

Stuff like this is very time consuming and addictive.

https://opencv.org/

 

Dammit. Wanted to find a video of using opencv as a mailbox alert, but got only projects without opencv:

https://www.youtube.com/results?...

 

But watching some video's of opencv can give you a good impression of what you can do with it:

https://www.youtube.com/results?...

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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Well, I've just received the 'MailChime' -- looks as if it might work.  Thanks again everyone.

 

I may sign up for informed delivery, but my main problem is determining when  the mail person drops stuff off on those cold dark days.

 

I don't want a text message in any event, plus it adds 2 more points of failure (wifi and cellular system).

 

hj

 

 

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RN42 is low power; its range might make 80m with a whip antenna.

RN41 is higher power and can reach 80m as is but it's 2.5mA typ deep sleep

SparkFun Electronics

SparkFun Bluetooth Modem - BlueSMiRF Gold

https://www.sparkfun.com/products/12582

...

We’ve tested these units successfully over open air at 350ft (106m)! 

...

(RN41)

"Dare to be naïve." - Buckminster Fuller

Last Edited: Thu. Feb 1, 2018 - 01:58 AM
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Add a smoke detector... Give  Sell some cigarettes to the postman

Last Edited: Thu. Feb 1, 2018 - 09:01 AM
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Perhaps Gauloises?

 

Ross McKenzie ValuSoft Melbourne Australia

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Hate Gauloise (you can find them in France, but people prefer winston, camels, pall mall 90% .Belgian ones are better : cheaper ; when Roma were/are deported - had to go out of France for lack of resources, but are free to come back as citizens of European countries, went/go to Belgium, register(ed) they ha(ve/d) been deported, buy(ed )as many cigarettes as possible... and c(a,o)me back)

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dbrion0606 wrote:

Hate Gauloise (you can find them in France, but people prefer winston, camels, pall mall 90% .Belgian ones are better : cheaper ; when Roma were/are deported - had to go out of France for lack of resources, but are free to come back as citizens of European countries, went/go to Belgium, register(ed) they ha(ve/d) been deported, buy(ed )as many cigarettes as possible... and c(a,o)me back)

I used to love Gauloise, Disque Bleu, Boyards, St Michel. All those lovely dark tobaccos. Sadly they've mainly disappeared these days, as the big tobacco companies buy up all the tobacco and blend it into one big, uniform "Malboro" taste.

Oh well, it doesn't really affect me, as I stopped smoking 14 years ago.

Quebracho seems to be the hardest wood.