voltage
How to change the range of antenna for non-contact voltage detection?
For example I would like to detect 220 VAC at 1 cm, 2 cm or 5 cm.
Can I make these changes with potentiometer?
I attached my circuit
TNX
if I find 220 volts at a distance of 10 centimeters in normal mode, I want to change the distance between 1 cm to 10 cm with a 2 key or one potentiometer or one keys .
what should I do ?
Something like this:
simulate this circuit – Schematic created using CircuitLab
For a real circuit you'd want a bypass capacitor across the supply and probably an RC low pass filter on the input.
The comparison voltage is 9.0V when the relay is off and 5.0V when the relay is on, so there is 4V of hysteresis. That is achieved by the R1/R1 divider and D1/R6 sets the hysteresis when the relay is on.
Q1 will drive a relay up to about 100mA coil current. D2 is a flyback diode to deal with the relay coil inductance.
R4 is to prevent output leakage from being amplified by Q1, R5 sets the base drive current when the 12V relay is on.
You need to use a low-dropout regulator between your input supply and your LED strip.
You can use a linear regulator, like LM2940-12, but this may dissipate too much power. You can work out the power dissipated in a linear regulator by multiplying the worst case voltage drop (Here it is 15.2 - 12V) by the current (0.61A per foot). The LM2940 is 1Watt, so you could power at most 1/2 foot (0.3A x 3.2v = 0.96W ).
If you need to power longer lengths, you should use a switching regulator. LT8610 will give you 2.5A with high efficiency. That would be enough to power 4 foot of your LED strip at 0.61 A / foot.
Best Answer
1) The "10 cm Plastic wire" is confusing, what should be used is an isolated wire so that it is IMPOSSIBLE to make (conductive) contact to anything and especially mains voltages (220 VAC).
2) this circuit actually work on capacitive coupling between 220 VAC, that "Antenna" and also capacitive coupling between you (your hand) holding the circuit. This capacitive coupling causes small AC currents to flow and the circuit detects those.
3) To improve sensitivity, you could increase the capacitive coupling. This can be done by not using a wire as the antenna but a small metal plate of 2 x 2 cm for example and mounted at the inside of a plastic box. Like the wire it needs to be isolated so the plastic box is needed. Then also place a second metal plate (or something else conductive) inside the box on the side that will be closest to your hand.
So: it is important to remember that the circuit including everything connected to it should be inside a plastic box. That's the only way to make it safe to use to detect 220 V AC. If you ignore this advice, you're risking your life!
Last remark: this is a simple circuit, I believe it can work provided there is enough capacitive coupling to the 220 V AC. But you might not be able to reach the 5 cm, for that you might need a more advanced design.