Frequency of crontab calling a php function - Looking for alternative options - php

Question

I'm programming my own "smart home" as a learning project.
My code is running fine. I'm looking for help to improve the efficiency and of the code and/or the setup of crontab + php code.
I'm monitoring the energy consumption of my washing machine with a WIFI energy meter. Target is to notify me once the washing machine is completed so I don't forget to clear it.
on my Pi I have a crontab like so:
*/20 7-22 * * * /usr/bin/php '/home/holger/html/plugs/washer.php'
which runs following php code (I simplified for better readability):
[...]/I call the function, of course, but this function does the main task
function loop($maschine, $watt_init, $trashhold){
$max = 75;//max loops to avoid endless runs
$i = 1;//start counter
$tackt = 3;//tact time to check energy consumption
//$trashhold = 4;//ab x Watt kein standby
if ($watt_init < 1 ) {//Machine is switched off if energy consumption < 1 Watt
die;//quit
}
elseif ($watt_init < 2 ) {//Machine is switched off or in standby if energy consumption < 1 Watt
die;//quit
}
else {//Any thing else: Machine is running
while ($i < $max) {//loop as long as max loops are not reached
$watt_current = json_combine(IPplug5);//getting current energy consumption from WIFI energy meter via JSON
sleep(60*$tackt);//sleep and continue every 60s x tact time
$i++;//increase counter +1
//compare actual consumption with defined trashhold
if ($watt_current[0] >= $trashhold) {//continue while energy consumption bigger then trashhold
continue;//repeat loop
}
elseif ($watt_current[0] < $trashhold) {//stop if energy consumption lower then trashhold
break;//stop loop
}
}
echo "Program done. please clear. Runtime: " . $i*$tackt. "Min."
//[...] message me to my telegram bot
}
}
The code is running fine and I'm getting the output I need.
My question is: Is there a better way to do that?
Currently I'm afraid to overload my Pi with too many open php sessions, therefore I'm starting the code only every 20min and also let the while loop sleep for 3 Min. But for improved accuracy I like to run the cronjob more often and also let the while loop sleep only for 30s.
My requirements are to stick to my PI and php code and not to use any available software like Home Assisant.io as it contradicts with my learning approach.
Any ideas or insights welcome.

Answer 1

Ideally it's a not the best approach to handling and measuring power consumption. It would be best if you created an API that accepts events like on/off or threshold hold limit extends from your IP devices.  Further you can create logs and store them in databases.
Although, for your current problem here is one alternate solution.
Set your cron that runs every second.
function get_powerConsumption($machine, $watt_init, $threshold)
{
if ($watt_init < 2) {
exit();
}
$time = date("Y-m-d H:i");
$filename = $machine . '_power_consumption.log'; // expecting some machine identification name here. otherwise ignore prefix
$watt_current = json_combine(IPplug5);
if ($watt_current[0] >= $threshold) {
$data = array(
$time,
$watt_current[0]
);
file_put_contents($filename, json_encode($data) . "\n", FILE_APPEND);
} elseif ($watt_current[0] < $threshold) {
$data = array(
$time,
'stopped'
);
file_put_contents($filename, json_encode($data) . "\n", FILE_APPEND);
}
}
Create another cron to look up for stopped events logged in the file. if found process the calculation based on logged data like time and consumption. You can set this cron to run based on your need like every second or minute or after some interval.
Also, handle code to delete old logs, once stopped events found.