LoRa should easily do what you need, how much data do you need to transmit and how often? It should be pretty easy to get 48h of battery life.
LoRa is definetly planned. I have to cover up to 1000m open ground.
My plan so far is to use "dumb" sensors. The sensor consists of the schematic from my last post with a slight variation. I will add another 2n222 to switch the transmitter on and of if a signal is detected. And a transmission is needed. So far this works.
The receiver, for up to 10 Sensors will consist of a uC, a receiver module and 10 decoders + one LoRa module.
I need to transmit, in this case, 12 bits from the sensors to the receiver, but, at the worst case, up to a few hundred times in a minute. (But not all sensors are transmitting constantly). But i only need this transmissions for a maximum timespan of 12 hrs, with up to 1 hr between the next events.
With the LoRa modules i plan to send the gathered data to a "base" station but only if the data is requested. And there the data would be nothing more than an array of 10 integers.
I just meassured the current draw of one of the sensors (but without the encoders, they will arrive on wednesday) and while transmitting it is arround 40mA and while idling arround 22uA.
I have not decided on what batteries i will use but mit 2400 mAh AAA (4pcs) i will get arround 3 1/2 years of battery life
so i think i could downscale this a little bit and just use 2 Cr2032.
A piezoelectric element has a high impedance. You may get better results using a JFET op-amp which has a high input impedance such as the TL081/TL082, especially at high frequency. The TL082 is a drop-in replacement, more-or-less, for the LM358. I typically use JFET op-amps on piezo disc guitar pickups and the like.
The TL082 is a drop-in replacement, more-or-less, for the LM358.
Well, mostly 'less' in this case. A TL082 will NOT work in this circuit.
LM358 has common mode range to ground, while TL082 is 3V to VDD. In other words, the piezo needs to output at least 3V before the TL082 'sees' it.
I will have a look at them and test them out. The only thing that could happen is that it will not work.