Voltage Detector

[raschemmel]

Please confirm what happens when you short the copper strip to your circuit GND.

[Joes]

right my circuit looks like this:




i did try your theory (dlloyd) but led just stayed on.

The 220R i have increased it but it did not seem to help.

i have been using a voltage from 7 to 24v from a power supply.

shorting the copper strip to the circuit GND made no difference but if i short it to vcc (through a resistor) the LED go's out.


This is what i am seeing over the LED when voltage is present:



so are we looking at a capacitor now?

[dlloyd]

so are we looking at a capacitor now?

I would try 100µF across the LED ... this will give a time constant of 22ms.

[raschemmel]

shorting the copper strip to the circuit GND made no difference but if i short it to vcc (through a resistor) the LED go's out.

According to the schematic, shorting the strip to Vcc should blow out the base of the first transistor because there is no base resistor.

[raschemmel]

This is what i am seeing over the LED when voltage is present:
   

You must be in Europe. That's 50 Hz.

The led is always going to be dim when driven by a 50 Hz signal.

Is there any waveform with nothing touching the copper strip ?

[Joes]

nothing touching the copper strip:




with a 100UF over the LED:




yes 50Hz here 

[dlloyd]

The capacitor should make the LED stay OFF longer when a signal is detected at the copper strip.

[Joes]

but as you can see in post 20 pic two, after adding a cap the led is now on more than before

[raschemmel]

What is the point of this project ?
WHAT EXACTLY do you need this for ?

[Joes]

What is the point of this project ?
WHAT EXACTLY do you need this for ?

i am making a relay card with a trip led on it to let you no that the power source has been lost, so i am switching 230v supply but there is no neutral local to the relay card. so thought this would be a good route to go but maybe not.

[raschemmel]

Can you use one of these ?

[Joes]

would like to keep it all on the PCB and is a lot more money 

[CrossRoads]

The relay card has 9V battery, you want it to turn on an LED when 230V that the relay contacts are switching is lost?
How about something like this?
AC from relay comes in, divide it down and rectify/filter it to a reasonable DC level, drive the base of a P-channel MOSFET.
When AC is present, MOSFET is off.
When AC is lost, Gate is pulled low, turning the MOSFET on and lighting the LED.

If not, please clarify your requirement further.

[raschemmel]

Why not replace led with optocoupler ?

[Joes]

(CrossRoads) thanks for your input that looks spot on few question:
1 The two first resistor (the divider) what resistances would you recommend? i have had a play with a volt divider calculator but was getting random numbers.
2 i have be using those diodes so do you think they would be adequate? Diode
3 100UF for the capacitor?
4 Resistor next to the cap 10K?
5 do you think this is an adequate Mosfet? Mosfet


Thanks Again