Help me with a current sensing project

current sensing

hello...

hope u could help me guys... my project involves detecting if there is current flowing in outlets and bulbs in a house...
i need 5 volts, if there is current flowing around .08 amps til 2 amps, O volts if there is no current...
The current sensor i found from Allegro.... needs 50 Amps to have an 5 volt output


any suggestion guys.... thank you very much in advance...

Re: current sensing

Read the article 80A Meter at Silicon Chip may be u get some

current sensing

You can simply connect amplifier to the output of your current sensor.

Re: current sensing

I agree with the amplifier configuration. But it needs to be a transimpedance amplifier

Re: current sensing

hi,

from you description, i think you only want to know whether or not the circuit is on or off. since if current then 5v else 0v.

the easiest way is connect a realy (depend on your power supply) and the other end connect it to a 5v power supply. connect output to normally open end.

wisely

Re: current sensing

wisely77 said:

the easiest way is connect a realy (depend on your power supply) and the other end connect it to a 5v power supply. connect output to normally open end.

Click to expand...

Would be nice to know cheap relay which can be driven by 0.1 V and 0.1 mA
Can you suggest any?

Re: current sensing

Hi,

There is anothe way to solve your problem ( And it works fine). Take a Optocupler that has LED in both directions, and connect each pin to the 220V with a 100K res in series. i.e. your power 220V through a resistor 100K to the opto and back through a 100K to the ground of the 220V. on the other side connect the Collector to a 10K pull up to 5V and to the PIC. the Emitter conect to ground. between the C and the E connect a 0.1uF capacitor.
See attached file.
Thats all.
Good luck.

current sensing

The best way is to get a current sensor that can be triggered by current in resolution of 0.01 per step.

I think allegromicro makes some of those.

Re: current sensing

chardbiggie said:

hope u could help me guys... my project involves detecting if there is current flowing in outlets and bulbs in a house...
i need 5 volts, if there is current flowing around .08 amps til 2 amps, O volts if there is no current...
The current sensor i found from Allegro.... needs 50 Amps to have an 5 volt output

Click to expand...

New product from Allegro for +/- 5A current sensing:
ACS704ELC-005

Re: current sensing

gidimiz said:

There is anothe way to solve your problem ( And it works fine). Take a Optocupler that has LED in both directions, and connect each pin to the 220V with a 100K res in series. i.e. your power 220V through a resistor 100K to the opto and back through a 100K to the ground of the 220V. on the other side connect the Collector to a 10K pull up to 5V and to the PIC. the Emitter conect to ground. between the C and the E connect a 0.1uF capacitor.

Click to expand...

You method could work OK only for 220V voltage detection. But the problem is CURRENT detecting! To make your method work for current detecting, you have to break current wire with resistor and measure voltage drop on this resistor. Then the next problem will arise: what should be the value of this resistor. Also, you have to worry about break voltage for back diode in your optocouple - sometime you will need more that one back diodes in serial.

Re: current sensing

we got this from the internet...

But we can't detect 4mV from the coil...

what could be the problem? will this circuit really work?

AC Line Current Detector
This circuit will detect AC line currents of about 250 mA or more without making any electrical connections to the line. Current is detected by passing one of the AC lines through an inductive pickup (L1) made with a 1 inch diameter U-bolt wound with 800 turns of #30 - #35 magnet wire. The pickup could be made from other iron type rings or transformer cores that allows enough space to pass one of the AC lines through the center. Only one of the current carrying lines, either the line or the neutral should be put through the center of the pickup to avoid the fields cancelling. I tested the circuit using a 2 wire extension cord which I had separated the twin wires a small distance with an exacto knife to allow the U-bolt to encircle only one wire.
The magnetic pickup (U-bolt) produces about 4 millivolts peak for a AC line current of 250 mA, or AC load of around 30 watts. The signal from the pickup is raised about 200 times at the output of the op-amp pin 7 which is then peak detected by the capacitor and diode connected to pin 7. The second op-amp is used as a comparator which detects a voltage rise greater than the diode drop. The minimum signal needed to cause the comparator stage output to switch positive is around 800 mV peak which corresponds to about a 30 watt load on the AC line. The output 1458 op-amp will only swing within a couple volts of ground so a voltage divider (1K/470) is used to reduce the no-signal voltage to about 0.7 volts. An additional diode is added in series with the transistor base to ensure it turns off when the op-amp voltage is 2 volts. You may get a little bit of relay chatter if the AC load is close to the switching point so a larger load of 50 watts or more is recommended. The sensitivity could be increased by adding more turns to the pickup.

Re: current sensing

Hi there,

look guys, we talking about a high current AC voltage so the solution is clear,
the best, is to using coile to Sense the current & it's work easy & simple,so forgot about resistors.

also do not forgot about high voltage & isolation , using coil will solve the isolation
problem too.

hope help,
mosh

current sensing

actually we need low current sensing...
the schematici post above...
can it really work?
can a coil really sense current from AC line with a current as low as 250 mA.... ????

Re: current sensing

can it really work?

Click to expand...

yes, why not ? [actually it is 80mA not 250mA!!!]
with 1000 - 1500 round [ even 800 could be enough ] turned directly on the wire
[I mean on shild of wire!] you can get the thing you need.
accrding to the above sircuit then you just need to amplify the signal you get from
coil...., then make output DC with a diode [the diode between two opamps] and
then simply filter it with a RC filter [like above sircuit ].... .
you already have every thing except logic levels [the simple part]!!.
an ordinary comparator like LM393 for detecting voltage and making the levels.
if you suply your sircuit with 5V you will get TTL logic levels on output.
[=> LM393 is open-collector output so DON'T FORGET pullup resistor]

hope helped
mosh