@ben999
But also look careful at the smokealarm PCB, as you might be able to reuse this to ensure that you are using resonance frequency

@ben999
I guess you don't hit resonance frequency.
Why not scavenge a piezo from a smokealarm, then you you know that the circuit is made for resonance frequency.
BTW I did not write MY piezo is working at 30V, I directed to a piezo that Adafruit is using, and that uses up to 30V - just to correct that I hvae not used the pieo myself

Adafruit have this one, can you try to make your setup similar? Notice that you need to oscillate it at resonance frequency to provide loudest beep.
Piezo buzzers are used for making beeps, tones and alerts. This one is petite but loud! Drive it with 3-30V peak-to-peak square wave. To use, connect one pin to ground (either one) and the other pin to a square wave out from a timer or microcontroller. For the loudest tones, stay around 4 KHz, but works quite well from 2KHz to 10KHz. For extra loudness, you can connect both pins to a microcontroller and swap which pin is high or low ('differential drive') for double the volume.
https://www.adafruit.com/product/160
And maybe your piezo is just a quiet buzzer - try to scavenge a piezo from a smoke alarm, that will give you around 105dB, and notice they have 3 pins and not only 2 pins
https://electronics.stackexchange.com/questions/18212/whats-the-third-wire-on-a-piezo-buzzer

@zookazim
Hi as the below circuit shows, the sensor read the electricity usage form the meter via IR, the meter have a Ir LED that transmit the usage, this can be picked-up/read with a IR receiver LED/transister. this is via the electrically circuit providing the data to the Arduino, this can if the protocol is correct, convert this to useful data

https://github.com/prophetmaster/landisgyre350/blob/master/images/Arduino-IR-Collision-Detection-Module-Pin-Outs.png

not sure what you exactly are searching for, did you check here?
https://kicad.github.io/footprints/Converter_DCDC

My car uses IR for automatic wipe the windshield, light are reflected if it hit a rounded surface, if there are water drops, then less light are reflected and wiper start to clean windshield
https://en.wikipedia.org/wiki/File:Rain_sensor_en.svg

Yes it's all fine to say goodbye, but maybe you should try RFM69 as most of those NRF24L01 are fake from Chinese suppliers, and that could have given you the bad experience, and if you also use WIFI on 2.4GHZ and Bluetooth devices, then 2.4GHz is quite crowded.
I myself also live almost in a Faraday cage, forcing me to have WIFI gateway on both my groundfloor as well as have one WIFI gateway on 1 floor, with cable to both WIFI gateway. Funny enough my Zwave 868MHz devices are having good coverage in whole house (Yes maybe it's due to Zwave have mesh network (not battery devices), and my battery Mysensors have mesh disabled)

@kalina
Yes it's very impressing what you have achieved

@bjacobse
Just to add a little more info about adding a GND plane to your PCB
I work in a electronic company, not doing PCB layout there though.
but we have a TV adapter which have 2.4GHz transmitter. and this PCB is GND on both sides and with plenty GND via's (all the small holes) to ensure good grounding

In case you wonder what it is, then it's an Oticon TV adapter 3.0
Clear Opn pairings with TV Adapter 3.0 – 00:34
— Oticon USA, Inc.

Yes anyone have developed something like this, Price US$30 so it's not worth doing it yourself, unless that you really want to do it yourself

https://www.oregonscientificstore.com/p-12-oregon-scientific-aw131-grill-right-wireless-talking-bbqoven-thermometer.aspx