Thank you so must for your help !!!!! I put up a 2nd post where I say it's not so much the battery I care about , it's the wire I must use that has 6 and 12volt at different times , I want to tie on to that wire but I only want it when it has 12volt not 6volt . So I must stop 6volt from coming out of that wire that I must use . Please get back with something like you sent me and how to wire it up .
I Thank everybody so much for your ideas and remember that I am new at this so make it easy so I can understand .
I'm not sure what you want. The circuit I posted can cut-off at any voltage between 2.5V and 36V, which can be altered by changing the values of R1 to R3.
The cut-off voltage can be calculated, using the following formula:
V = V
REF*(1+R1/R2)
Where V
REF = 2.495V but can normally be rounded to 2.5V to make calculations easier.
R3 controls the hysteresis. When the output is off, it's in parallel with R2 (assuming the load on the circuit is a very low resistance compared to R1 to R3) and when the output is on, it's in parallel with R1. This means the turn on voltage of the circuit is higher than the turn off voltage, which is necessary to stop the circuit from oscillating. Without the hysteresis, when the circuit turns off, the load would be disconnected from the supply, causing the voltage to rise and it to turn on again, resulting in an endless loop.
This means there are two separate calculations for V
ON and V
OFF.
V
ON = V
REF*(1+(R1|R3)/R2)
V
OFF = V
REF*(1+R1/(R2|R3))
The | character means the equivalent of two resistors in parallel, so R1|R3 = (R1*R3)/(R1+R3) and R2|R3 = (R2*R3)/(R2+R3).
With the values in the circuit above: V
ON = 10.6V and V
OFF = 10.2V rounded to 1 decimal place.
To make calculations easier, don't worry about the separate on and off voltages, just use the first formula.
By the way, the LM358 is totally different to a comparator IC, such as the LM393. It is an operational amplifier. It can be used as a comparator but it's seldom the best choice of that function. It's more suitable for amplifying