Im trying to get my head using a 555 timer to effectively make the opposite of this circuit below.
The problem I want to solve is more for my own learning about 555 timer circuits more than anything.
My setup is the opposite filling/drain of the image below as I am trying to empty a tank when it fills not keep a tank always full. In my setup the tank fills up over time and the pump will drain it when it hits the top connection and continue to pump until the low level connection breaks.
The issue is for my setup that I have to use the NC connection on the relay. When I power the unit with no water in the tank the 555 timer is ON (for me the tank is empty when I turn it on) and it will only go off when the the all three probes are triggered ie the tank is full. This is fine as I can just use the NC on the relay but it means that the 555 timer is triggered ON when the pump is OFF and OFF when the pump is ON. It also means that when I power it on for a brief second the pump will turn on until the 555 timers initiates.
Again this is mainly for me learning about 555 timers but I would to design a circuit that is OFF when there is no connection on the probes. Then goes ON when both the lower and upper probes are triggered then off when the lower probe breaks. ie the opposite of this unit.
I hope this makes sense and help is very appreciated, I haven't been able to find what I need only yet but Im looking.
You should also move it from between GND & Load to between Vcc & Load, and probably remove the 180K pulldown resistor.
Another thing to keep in mind is that pin 4 of the 555 (reset) should be powered with a small delay using a capacitor and resistor, to prevent the 555 from being triggered at powerup.
Awesome, sorry for the late reply, I got pulled into something else at work.
Are there any popular PNP transistors that are commonly used in these types of applications. I haven't had much experience with using them so Im unaware if there are any very popular ones that are recommended
For the delay, a quick google can see 10 kΩ and a capacitor of 100 µF should give a 1 second delay on start up. Was that the kind of delay you were thinking.
Nah. Don't use a transistor at all.
If this is a common 555 (not a mosfet type), then it's output can directly drive a relay.
connect whatever was connected to the collector directly to pin3 of the 555.
No R5, R8, Q1.
That also will invert operation, as requested.
Leo..
Long time ago here too, although I recently designed an 38kHz beambreak with a MIC1555, which refreshed my memory. The 555 was an important building block in the eighties. Many example books were written about them.
Leo..
Incredible they could get all those transistors, resistors and flip-flops on a near microscopic chip.
I remember my last project was trying to make an accurate "long" timer by making the 555 "multivibrate" at about 30Hz with small caps, then dividing with binary counters. Think I got to 1 second in 15 minutes, then had to retire from playing and "go to work".
