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1  Using Arduino / General Electronics / Re: Using a transistor instead of a relay as a button on: July 28, 2014, 10:11:48 pm
Why am I confused as hell from this post.....

Use a transistor instead of relay, yeah no problem... then I get lost due to a resistor between arduino's pins.... maybe it's the lack of provided circuit throwing me..

So are you sensing the 12v voltage?  Then acting on it?  Do you wish to provide 12v from a transistor (a switch?)

2  Using Arduino / General Electronics / Re: Switching the Dimmer 'on' and 'off' affects my computer on: July 28, 2014, 12:13:14 pm
Even a picture of a hand drawn diagram will be good, in jpg, png or pdf format.

I noticed. When the computer makes that beep sound, I stopped receiving data from the Arduino in my Matlab GUI. Thanks

240v linked to ground?

Normally I'd have said the relay's emf is to blame, but the last circuit you posted suggests mains voltage is shared.
3  Using Arduino / General Electronics / Re: transformer's centretap. on: July 27, 2014, 06:02:44 am
I was close enough, the answer is what i dreaded you'd say...  thanks seeing it is you. 
4  Using Arduino / Project Guidance / Re: Car power supplying Arduino?? on: July 27, 2014, 06:00:41 am
it sounds like something's drawing too much current already that or the battery simply can't provide the cca required to crank over the engine, the start motor could be also on it's way out? whatever the cause...

I think trickle charging a small battery so it's under it's own power when the alternator is off this gives a UPS effect.
5  Using Arduino / General Electronics / transformer's centretap. on: July 26, 2014, 12:25:20 pm

In all of the inverter circuits I've seen they all have a ct pin, on a transformer without one, I presume  I have to energize the entire primary coil at 50hz ?
6  Using Arduino / Project Guidance / Re: Need to make an audio amp, maybe with lm386 on: July 26, 2014, 01:00:45 am
.5watt speaker will sound tinny at best regardless of amp...

Is the lm386 not automatically set to a gain of 10? / .25watt? Sounds ideal, you can change the gain higher and use a pot on the input signal.
7  Using Arduino / Project Guidance / Re: Is 5.5volts from external regulator to Vin pin enough?? on: July 26, 2014, 12:57:45 am
Ideally 7-7.5v
8  Using Arduino / General Electronics / Re: Arduino Due + LED Resistor Requirements on: July 25, 2014, 06:43:38 pm
The due has the least voltage/current vs say an uno eg 3.3v vs 5v

So you're not going to get very brightly lit LED's are you using 5mm uv leds or more powerful ones?
9  Using Arduino / General Electronics / Re: arduino-18650 charger-help. on: July 25, 2014, 06:38:54 pm
You wish to charge the connected batteries to arduino?

Except, you require > 8v  to charge 2 batteries in series, and then it becomes tricky, charging 2 individual batteties via 5v is the easier option.
10  Using Arduino / Project Guidance / Re: Using LDR as a alert at anytime during program on: July 25, 2014, 12:15:09 am
I don't unde and how you mean you can send it once?

Why not call xively before the twitter post? The code I understand but the system ie how to post tweets, what are the steps involved!
11  Using Arduino / Project Guidance / Re: Car power supplying Arduino?? on: July 25, 2014, 12:04:14 am
The car has a average voltage of 14.4vdc, and will not start below 13vdc. 



Average voltage is 14.4v is it?
Car refuses to start under 13v

And who took these measurements?   Average voltage from the alternator is around 14v the car would have issues if the battery read 11.5v (starting it) but 12.5v to 13v is plenty to turn the starter motor...

 your values seem off.
12  Using Arduino / General Electronics / Re: What areas of electronics are useful to learn about for arduino projects? on: July 23, 2014, 12:29:44 pm
I once had a teacher/supervisor who grumbled on about how students now just use an mc to do the work over the use of good old logicchips...

I guess it boils down to what you want to do, no point learning about low pass filters if all you want to do us blink an led and make it go beep
13  Using Arduino / General Electronics / Re: Wind generator for 12v battery - no controller? on: July 23, 2014, 11:17:15 am
The turbine can supply peaks higher than 14.5v but the current is lacking to do any real damage. Since the motors rated for lead acid it will produce aroind 14-18v with a light load, but the battery will suck up the current and not go over, unless it happens to produce stupid amounts for current/voltage..

People use 240vdc rectified and fed into 12v batteries to "regenerate" them... as long as it does not boil and run out of water/acid it's practically happy

But sticking a 14.5v switching regulator on the output is the best way for a lead acid.

14  Using Arduino / General Electronics / Re: can this led be powered off arduino digital pin? on: July 23, 2014, 11:10:15 am
Awol is correct  but he forgot to add up to 40 ma with current limiting or you will kill your pin.
No, he didn't forget - that's what "up to the pin's absolute maximum current of 40mA" means - the current limit is implicit.

The pin will max out and supply possibly higher current than that for a while.
15  Using Arduino / General Electronics / Re: 110V detection on: July 23, 2014, 11:08:36 am
I'm trying to find an solution that is easy to implement for my problem.

I'm using arduinos to control 5V/10A relays to switch on and off lights, plugs and heaters.
For the lights, the relay has all the 3 wires connected, so you can use it with the wall switch too.

I would like to detect via the arduino if the light is on or off, because the arduino knows the state of the relay, but not the state of the wall switch, and to call a light on or light off command would require to detect if the light is on or off.

I tried at first with a current sensor: ACS714. I don't want to measure the amount of current but just to tell if the current is on or off.
My problem is that since I use LED lights, they seem to have a too much low current consumption: 5W, 45mA, so between power on and power off, I see no difference in my readings. I calculate the average current in a 50ms delay.

My code is the following:
boolean isLightOn(int analogPin) {
  int count = 0;
  float currentSum = 0.0;
  int counter = 50;
  while (count < counter) {
    currentSum += abs(analogRead(analogPin)-510);
  return (abs((currentSum/counter)) > 3);

Does anyone have an idea on my problem ?
Is my assumption correct ?
Is there another option to detect if the power is on or off ?

My first thought is an opamp, as a comparitor so you get back a high/low signal using a pot to fine tune.
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