current/voltage sensor?

I designed 2$ current sensor, look in part 2-1, see if you may find it useful: http://coolarduino.wordpress.com/2013/02/08/power-meter/

Hello,

I have found on ebay a cheap non-contact voltage detector. http://img.inkfrog.com/pix/gomepls/18252_3.jpg I ordered one and it actually works: The led turns ON whenever its close to a wire with electrical current, and goes back OFF when its far away.

So I though: I'll just open it and re-use the circuit in my project, so I can detect whenever the relays are ON or OFF. I can measure the voltage drop on the LED in order to know if the detector circuit its detecting voltage or not. I dismantled it and powered it with 3V to test (equivelent to the 2XAAA batteries that it uses). https://www.dropbox.com/s/u9d8uy6s7dmjdy4/2013-06-12%2021.34.07.jpg

However, when is not fed by batteries, the LED is always ON, making the detection circuit useless. I tried back again with the AAA batteries and it works fine!

Am I missing something here? Any idea why is working with batteries and why is not working with a wired power supply?

Thanks, Jooabs

Cool!

Please trace the circuit to see if it use CD4069. then only D1, D2, D4 is needed, one CD4069 will be able handle 2 AC chanels.

http://www.fairchildsemi.com/ds/CD/CD4069UBC.pdf

joaoabs: However, when is not fed by batteries, the LED is always ON, making the detection circuit useless. I tried back again with the AAA batteries and it works fine!

Am I missing something here? Any idea why is working with batteries and why is not working with a wired power supply?

Use optocoupler to replace LED, this will be isolated between. Use isolated dc supply or wireless power module to power up the board. Use decouple cap at 3 V power. put small cap at input of IC for low pass filter.

Hi,

Thanks for your reply. Yes, the circuit seems the same as the one you show. In my case, the IC is the 74HC14D.

sonnyyu:

joaoabs: However, when is not fed by batteries, the LED is always ON, making the detection circuit useless. I tried back again with the AAA batteries and it works fine!

Am I missing something here? Any idea why is working with batteries and why is not working with a wired power supply?

Use optocoupler to replace LED, this will be isolated between. Use isolated dc supply or wireless power module to power up the board. Use decouple cap at 3 V power. put small cap at input of IC for low pass filter.

What I don't understand is why should I replace the LED by an optocoupler. The circuit itself is contactless (It should only touch the plastic of the wire, not the metal), so why the need to isolate? Also, could you please provide more details on "Isolated DC supply or Wireless power module"? In my test I used a 220VAC/12VDC power supply, and then on the breadboard I used a step-down to 3V based on LM2596, like this one:

http://thmb.inkfrog.com/thumbn/geiliablestore/LM2596_001.jpg=450

So I think the 3V already have decouple capacitors, right? How can I isolate further the power supply? And finally, what is a wireless power module?

Thanks, Joaoabs

Isolated dc converter;-

Linear technology has nice video which last 4:37. Isolated power supplies Linear

Improved Power-Supply Rejection;-

Maxim integrated has nice web page about it,

  • Second-order cascade RC ripple filter
  • LC Filter
  • An Additional Linear Regulator

Improved Power-Supply Rejection for Linear Regulators

in your case Linear Regulator will does better job than LM2596.

Wireless power;-

Buick cuts the cord: Riviera plug-in concept offers wireless charging

http://www.gizmag.com/buick-riviera-plug-in-concept/27172/

wireless power module, Wireless Charging Module, Seeedstudio, $7.90

Do a search on ebay for Arduino Current Sensor. I was actually just looking for Arduino stuff and saw the current sensor modules. I thought about getting this one:

http://www.ebay.com/itm/5A-20A-30A-Bi-Directional-AC-DC-Current-Sensor-Module-arduino-compatible-/111085883206?pt=LH_DefaultDomain_0&var=&hash=item19dd3c0f46

Michael

There are a lot ways detect AC, but OP's way is the most coolest way.

if concerned reverse voltage of LED, use diode or ac opto isolator instead.

sonnyyu:

You could probably eliminate three of the diodes because half-way rectification would be adequate in this case.

Yes we could, all we need add one electronic capacitor at output half-way rectification.

or use this

since we face 24V instead of 110V, cap could be droped.

second one use Optocoupler with AC Input.

buy one from ebay?

Opto Isolation 4 Input Channels, Ebay, $18.00

only half of it shown.

mrmonteith: Do a search on ebay for Arduino Current Sensor. I was actually just looking for Arduino stuff and saw the current sensor modules. I thought about getting this one:

http://www.ebay.com/itm/5A-20A-30A-Bi-Directional-AC-DC-Current-Sensor-Module-arduino-compatible-/111085883206?pt=LH_DefaultDomain_0&var=&hash=item19dd3c0f46

Michael

Yes, I already tried similar sensors based on that same Allegro ACS712. However, for AC currents, the output will also be AC, and what I need is a logical "1" (or equivalent) so I can detect on a digital port. Check my initial post:

joaoabs: I used some ACS712 kits connected to a PCF8591 (I was planning to know if the appliances were on/off by reading the value on each ADC port). There are kits of 5, 10 and 20A. I tested a 5A kit, the datasheet says it will increase 185mv per Ampere. The appliance I tested is a 20w Led floodlight and therefore consumes around 90mA (220v AC). This means the ACS712 would increase 16mV when ON, which is difficult for the PCF8591 to notice any difference (8 bits). Also, since my appliances are AC, the output of the ACS712 is also variable (50 Hz).

So I gave up of detecting if the circuit is closed by current sensors, and I believe I need to approach this problem differently.

Basically I need a circuit that detects that the appliance circuit is closed (relay and internal switches) and then puts a digital pin at "1". I saw some ideas in the web with phototransistors, like the TLP620, but I'm not sure it could support voltages like 220V AC.

Any suggestion?

Thanks, Joaoabs

Thanks anyway, Joaoabs

sonnyyu: There are a lot ways detect AC, but OP's way is the most coolest way.

I had seen some schematics with similar approaches, but never quite understood how it works. Is it connected in series or in parallel? I have the feeling its in series...

My AC detectors should be able to detect if a 20W lamp is ON or OFF (low current), but also the same for an 2000W water-boiler resistor (~10A). Can these optocouplers handle such high currents? If they can, I believe I have my problem solved....

Looking at the datasheets of the PS2501 and PC817 (used on the board from ebay) there is the value of "forward current" and is ~1A....

Thanks, Jabss

I had seen some schematics with similar approaches, but never quite understood how it works.

C1 33nF 440V is function as step down transformer, and share between 2 channels.

Is it connected in series or in parallel? I have the feeling its in series…

in parallel.

Looking at the datasheets of the PS2501 and PC817 (used on the board from ebay) there is the value of “forward current” and is ~1A…

PC817

*Peak forward current 1A
*Pulse width <=100µs, Duty ratio : 0.001
Forward current 50 mA (max)

It might work well at 20 mA.

samething as PS2501

Anyone know of a optocoupler that can survive to 10A ?

Thanks, Joaoabs

sure, use small opto triac drive big one.

sonnyyu: sure, use small opto triac drive big one.

Thanks,

That seems a schematic to control 220VAC from an arduino/ucontroller, right?

What we have been discussing in this topic is the opposite: To make the arduino/ucontroller aware when the a 220VAC/2000W device is ON or OFF. For that, one possibility would be using an optocoupler, but since my devices can be form 20W to 2000W, the optocouplers need to handle 10A.

Any suggestion? Thanks, Joaoabs

You can use something like this http://people.ece.cornell.edu/land/courses/ece4760/FinalProjects/s2008/cj72_xg37/cj72_xg37/index.html

Hello again,

Just for the sake of completion of this topic, I found a solution in the web for the initial problem: A circuit that detects if an AC appliance is ON/OFF.

http://electronics.stackexchange.com/questions/33042/how-do-i-select-the-accompanying-components-for-an-optocoupler

Anyway, I'll only use this schematic if my solution with the non-contact voltage detector. I have ordered (still waiting) an isolated power supply and I'm hopping to solve the problem with it.

Cheers, Joaoabs

Hello again,

So I finally got my new isolated voltage sensor. I build a test circuit in a breadboard, did some tests (touching with the loose end of the resistor on some low-powered cables - my 20w soldering iron) and it worked. So I soldered the circuit in my board and strategically positioned the sensor near one cable that don't have current flow when the appliance is off.

Unfortunately, it didn't work. It seems this sensor only works when close together with both cables (neutral and live). The output varies too much and is not reliable.

Any idea of what may I be doing wrong?

Circuit: Photo:

Thanks, Jooabs

sonnyyu: There are a lot ways detect AC, but OP's way is the most coolest way.

Have you tried this? LEDs don't survive high reverse voltages very well, and this circuit has very high reverse voltages appearing across the LEDs in the optoisolators.

I don't see how voltage detection does any good, anyway. You want to know if the appliances are drawing power. That requires measuring current.

No, I haven't try it. I also suspected that the high-voltages would be too high for these components.

What I tried was the circuit I posted today. Conceptually, I don't see why it shouldn't work, but the sad true is that id doesn't and I'm back to square one.

Any suggestion of something that could work?

Thanks, Joaoabs

Well, 12k on 220Vac dissipates a bit over 4W, so you'd need 10W resistors, not 1/8W.

Why are you still trying to detect voltage? You have already said that relays may be on, hence presence of voltage, but the appliance may still not be drawing power. Measure the current.