I am interested in a small LoRa enddevice - with only a button - that sends out a package if the button is pressed.
So far - so good. Sounds easy.
But there is one special wish, that I am quiet unsure, whether it is possible to bild.
The whole device should be passive, and just powered through the energy of pressing the button, when it is pressed. I can imagine, that there is the possibility to use small solar panels and buffer-batteries, to load the device and store some energy to power that device. Due to the fact, that the device might be placed in dark places, that just sometimes get brigh, I am hoping, that there is a way to build a completely passive device, where the power is gained by “using it” / pressing the button.
I thought of something like using the piezo-effect, to gain the electricity that is needed to send one package.
Unfortunately I don’t have a real background of electro-technique, as well as know-how from the hardware behind the lora.
That is the reason, why I hope that someone of you has enaugh know-how to judge about this idea.
Do you thing, or better know, if it will work, or not?
I am looking forward to your constructive feedback and opinions on that special whish.
Sorry to disappoint you, but this will not work. LoRaWAN transmissions are energy effective, but not to the point where piezo generators will provide sufficient power.
A typical piezo generator will produce 0.000022 joule energy. One joule is one watt for one second, so you have 22 microwatt for one second to work with. LoRaWAN modules like the RN2483 require something like 40mA at 3.3 volt for at least 2 seconds to transmit, so 40 * 3.3 = 132 milliwatt for 2 seconds = 264 millijoule. That means 12000 times the available energy. That does not take into account energy losses while stabilizing the power, any additional power required by other hardware etc.
Oh, that’s ok. That are the nature’s conditions, that we have to deal with, so everything’s alright.
But first of all: thanks a lot for your great explenation.
Pressing 12 thousand times the button is not the right solution, so I have to look for the best alternative.
Did you mean, that a passive device won’t work in general, or just with the piezo system?
Another idea, that came in my mind, would be, that through the “button pressing” some mechanical wheel could be brought into motion. With the momentum kind a dynamo / generator could produce electrical energy.
Does that sound more realistic, or do you think, that the energy of pressing the button will never be (used) “enaugh” to reach the energy amount of neraly 300mJ?
Otherwise:
What would be - on your opinion - the best and most independent way to power a device like that?
… or a small solar panels? I didn’t calculate it but given that calculators run on tiny solar panels that must be possible, even inside. Except when it’s a basement perhaps.
This is definitely possible. Not with piezo but with a little coil. In fact, here’s an example of a product that does exactly that (not using LoRa but RF on 434MHz):
How often are you expecting a button press? Perhaps a tiny solar panel charging an ultracap would work? It may take several days (as you said… intermittent light) to build up enough of a charge to run it for a couple of seconds. And you’ll have to be careful of leakage current.
You might think of the concept of energy harvesting for your application.
Solar energy, motion, difference between warm and cold and even radio frequency can be utilized as a source of energy.
If you google on “energy harvesting iOT” you will find lots of information on this subject. May be this will help. For instance this product that harvests energy from radio frequency that is already in the air: http://www.getfreevolt.com/
But, first consider the use of a small battery. Why is that not possible in your application?
I would probably just stick a normal button cell on there, they provide enough current for infrequent LoRa transmissions for like nearly a year (think doorbell). Im looking at doing the same thing at my place, with a sensor for a mailbox. i.e. detect when mail goes through, send LoRa packet
thank you all for that greeat feedback.
Unfortunately it is already a few days since my original request, but it is still “current”.
@BoRRoZ
I button may be pressed one time a day.
Impossible is nothing - as the option to use a battery.
But to reduce “maintanance”-work, possible power leakage, etc. my original aim would be to build something “self-sustaining” and completely passive.
But if it should be not realizable I have to deal with it.
@niek
That product completely follows the idea of harvesting I was thinking of - or I was hoping to find.
Thanks a lot.
Do you know of any projects, where this harvesting technique is used to power a LoRa client, or where to product is modified, so it uses LoRa to send a package? Unfortunately I did now really find anything on the first view.
Or I have to look twice.
The reason why I want to avoid solar powering is, that the room where I want to install has no windows, and only is lighted when a person enters the room.
Also to the others who answered - a great thank you.
Looking again forward to all your feedback.
anyway, pushing a button once a day and use a low power Tx adds up to changing your little battery maybe once every 2 years ? is that to much maintaince ? or do you really want to spend a fortune …
Hello
I understand this may be a little off-topic, but I searched online and could not find anything useful:
What if you want to do that with a battery in the most efficient way with LoRa?
I am thinking of a Arduino Pro Mini 3.3 with a LoRa module, with the doorbell button working as a power-on momentary button to give power to the Arduino for a fraction of a second?
Would it have enough time to boot up and send a message?
Can you think of better solutions?
Thank you guys!
2- no. you won’t have enough time to boot AND to join the network AND transmit during the time off a button push (all network joins differ in time also)
3- better to use a little circuit that after one push of a button, power the arduino, do its thing and when ready switch itself off and ready for next push.
LoRa is primarily for long range communication, in the kms.
There are any number of simpler and cheaper RF modules that are OK for the very short range needed for a doorbell.
The real problem is actually nothing to do with RF modules at all but how you get a Pro Mini to operate long term from batteries. Thats not easy, better to ask in the Arduino forums.
A standard Pro Mini is next to useless for your application.
Thank you very much guys!
I’ll have a look at those circuits and see if I can use a shorter range RF that sounds reasonable.
Now I have something to work on!
