Yet another mailbox

  • Just for the fun of it I added some monitoring of the mailbox to my collection of MySensors items already in operation. I had no plans to show the project here because there are heaps of such displayed both here and there and the technological level is not much to talk about.

    But then I thought it might serve as an illustation of what can easily be achieved due to the excellent work made by the MySensors team (many thank's for the job done...) because almost everything was already available. All needed was:

    - A Sensebender Micro
    - The SensebenderMicro sketch
    - Two normally open reed switches 
    - Adding two interrupts to the sketch plus
    - A few other tweaks to adopt it to OpenHab

    The reason for using the less common normally open switches was to save some battery juice. These switches are triggered almost all the time and every time the sketch wakes up a normally closed switch will draw a little current but the savings might be marginal, if any at all.

    Here is the end result as shown by OpenHab:


    Guess the titles are obvious even though displayed in Swedish but the (rough) translation is:

    - Temperature
    - Humidity
    - Mail in
    - Mail removed
    - Battery mV
    - Battery %

    And this is what the installation looks like:


    Just an observation, during a recent cold period with temperatures down to -25C the readings from this sensor were the most accurate ones. Other readings based on an 18B20 could be far off even though both sensors are in range at higher temperatures.

    Have thought about adding a speaker function to say "Thank you, but please keep the bills" to see if this would trigger any reaction but so far have resisted the temptation 🙂

    That's all.

  • Hardware Contributor

    Nice 😊 how far away is the mailbox from gateway ?

  • Right now the gateway is located inside and upstairs towards the far end of the house in relation to the mailbox (25 - 30m) . So to make the mailbox work without any long range radio I had to add a repeater to a room facing the mailbox. This repeater was useful for other things as well (could switch some long range radios to the normal ones) so I felt OK to install yet another little power consumer.

  • Very nice project, i would also like to build this mailbox sensor.
    Could you please share the modified sketch and the tweaks for openhab... ?
    Thanks in advance

  • @sensorchecker I can of course share the sketch but need to do some more work on it before publishing anything. How do you communicate between MySensors items and Openhab?

  • Hardware Contributor

    Nice share! And interesting with the -25C. Could you estimate in figures the differences between the DS18B20 and this SensbenderMicro? How much in which range?

  • @mbj No hurry, at the moment i´m waiting for parts from HK and can´t do anything until they arrive.
    I communicate with an MQTT Gateway (Arduino Nano/ W5100/ NRF24l01) and MQTT binding (1.8.0) between the MySensor items and OpenHab (1.8.0).
    I will build some sensors like described in this thread
    One of them will be a mailbox sensor with your sketch...

  • @sensorchecker You may get a little job to do, the sketch is made for the Sensebender Micro and I have no idea how it will compile for the "slim-battery-node".

  • @m26872 I did not note the numbers but worst case was 4-6 deg C at -20 to -25 ( ie 18B20 showed -18 and the Micro -24).

    I should have replaced the 18B20 to see if it made any difference but it was so cooooold out there. Also I have a feeling that the Sensebender might have been slightly lower than the truth as well but clearly much more in line with other readings available.

    Right now the readings are +4.2 for the mailbox and +3.6 for the 18B20 and since they are at different levels this is perfectly fine.

    I have not checked the specs for either of the sensors and have also noted that there are numerous articles about calibrating the 18B20 but never bothered dive into the issue. And then also comes the issue if the ones I have are genuine or "Chinese clones".

  • Hardware Contributor

    @mbj Thx, I wont draw any scientific conclusions from your figures either. I was just curious. As you said there're always discussion about accuracy and working ranges etc.

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