I have a fish pond, and wants to detect if water is lower than given level A.
On level A I can mount a sensor.
The environment is outside and a bit harsh, so HW must be high quality, but not super expensive.
Function: when water drops under level A, I get an alarm.
My idea is to measure if there is water all is ok, when no water I get an alarm.
My initial HW idea is to use 2 pcs stainless steel connected to a transistor bridge(?) of 3 NPN to make an amplifier but I have no experience in using NPN like this
You posted your question in the "using Arduino" forum section. Do you plan to use an Arduino? If this is all the circuit will do, it would be a waste of an Arduino, I think.
But if you do plan to use an Arduino, I would connect the two stainless steel probes to a digital input pin and an analog input pin of the Arduino. Set the input pin mode to INPUT_PULLUP. then read the analog input. If the probes are above the water level, you should get a reading which is close to zero (but may not be exactly zero). When the probes are in the water, you should get a higher reading. You can choose a level between the two readings and use an if-statement to trigger your alarm.
The small current that flows when the probes are in the water could eventually corrode them even though they are 'stainless'. To reduce that, have the Arduino digital pin in INPUT mode for most of the time. Every few minutes/hours, have the Arduino switch to INPUT_PULLUP, read the analog input, and then switch back to INPUT. That way, the current will only flow for a moment each time a reading is taken, which will reduce any corrosion.
There are float switches that sense HIGH level, LOW level or both. They are built for "outdoor" use.
I use one in my drainage system that switches at a higher level than the pump. The switch is attached to a Raspberry Pi Zero in the basement and sends me an email every day so that I know it's still working and in case the level is too high an email very hour ...
Or - like suggested by @LarryD - a Float (liquid level) like this
Similar to my irrigation system that stores well water in tanks for the pump. The level is watched by float switches connected to an Arduino NANO. One switch turns on then the water reaches the low level and that tells the NANO to turn on the SSR to the valve letting more well water into the tanks. The second float switch tells the NANO the tanks are full and stop the SSR.
Has worked flawlessly for about 5 years! Not used during the Winter!
I agree with LarryD right off the top. I would be using a magnetic float switch. Especially with brackish water and a harsh environment. A simple stainless steel float switch.
Thanks @PaulRB
Correct it can be done without Arduino, but I will send result to home assistant that generates an alarm.
I was hoping that someone of you could confirm my transistor system will work with water, my system will work as a cable finder, but not sure if it will amplify a water "disconnect"
