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Topic: non contact voltage tester (Read 795 times) previous topic - next topic

tjones9163

Hello, I have a circuit below that uses Darlington pairs to increase the gain by a large amount. My guess is the high voltage oscillating devices Like (60 HZ) household devices and these devices produce a strong magnetic field and the antenna picks up these magnetic waves and since the gain is so sensitive, the base allows the magnetic waves to turn into a small current and actually to flow through the base and to the emitter, allowing for the current to flow from the collector to the emitter lighting the LED.

Is that the correct way of thinking of it? and the Website the i got the circuit from https://www.instructables.com/id/Non-Contact-Voltage-Detector-2/
and the site suggests 9v but I actually got the circuit to work with a coin cell battery.

Would using 9v allow for more range?


and what is the significance of the resistor values that they chose to use, with 5m ohms is used on the first collector of the transistor closest to the antenna and then the resistance valuse drops for each resistor going down the line?

Here is the circuit-----https://easyeda.com/editor#id=bb54f8e4a50d4775b5ca9899c618cd23

hammy

Not much Arduino in this project .
Can't you get in touch with the indestructible author ?

MarkT

#2
Jun 23, 2019, 12:11 pm Last Edit: Jun 23, 2019, 12:13 pm by MarkT
Hello, I have a circuit below that uses Darlington pairs to increase the gain by a large amount. My guess is the high voltage oscillating devices Like (60 HZ) household devices and these devices produce a strong magnetic field and the antenna picks up these magnetic waves and since the gain is so sensitive, the base allows the magnetic waves to turn into a small current and actually to flow through the base and to the emitter, allowing for the current to flow from the collector to the emitter lighting the LED.
No, not the magnetic field, the electric field is sensed directly by capacitive pickup.  To sense magnetic field you'd use a large coil.
Quote
Is that the correct way of thinking of it? and the Website the i got the circuit from https://www.instructables.com/id/Non-Contact-Voltage-Detector-2/
and the site suggests 9v but I actually got the circuit to work with a coin cell battery.

Would using 9v allow for more range?

Probably more sensitivity
Quote
and what is the significance of the resistor values that they chose to use, with 5m ohms is used on the first collector of the transistor closest to the antenna and then the resistance valuse drops for each resistor going down the line?
They are in proportion to the typical currents expected, each transistor will increase the current by a factor of 100 to 300 typically.  The resistors prevent the transistor burning up with over-current, probably not needed if the antenna is insulated though.  Setting them all to 100 ohms will protect just as well really.
Quote
Here is the circuit-----https://easyeda.com/editor#id=bb54f8e4a50d4775b5ca9899c618cd23
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tjones9163

Thanks for the response, Mark. Is there an equation to see how much current is flowing in the circuit?
 Is it correct to say that Q1 has the least amount of current according to Ohms law and then it gradually increases after each transistor going down the line?

wolframore

You cant measure current using the capacitive method. For that you would need the inductive coil.  Your contactless voltage sensor will light up even when there is no current flowing with only the AC voltage present at the wire.  They are just safety check with limited information.
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