http://arduino.cc/forum/index.php/topic,51638.msg368432.html#msg368432

http://www.radiolocman.com/shem/schematics.html?id=52242

I found this helpful:

http://jethomson.wordpress.com/2010/02/21/diy-usb-to-serial-cable-for-3usd/

I've seen people use two digital pins to get ac - with a soil moisture sensor.

here's an example
http://gardenbot.org/howTo/soilMoisture/

that same page also shows an H-bridge circuit

I know that you asked about usb - so I don't know if rf would work for you but here's one link:

http://alyer.frihost.net/thn128decoding.htm

I know the Practical Arduino book has a LaCrosse rf decoded - I think that someone used that for the Oregon Stations as well but I don't recall were I saw that - might have been in the arduido forum.

my ups had a very annoying beep . beep . beep - as if having no lights wasn't enough of an indication of no power - so other options are tapping into the beeper or the no power led
 

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120571109230&ih=002&category=4660&ssPageName=WDVW&rd=1#ht_1324wt_1163

doing a search on ebay for "ENC28J60"

this one is 9.44 includes shipping - but it looks like it doesn't have the 74HC
http://cgi.ebay.com/ENC28J60-LAN-Ethernet-Network-Module-AVR-51-LPC-STM32-/190548762559?pt=LH_DefaultDomain_0&hash=item2c5d975fbf#ht_3757wt_1163

I see that the picture has an embedded name on it - I found an ebay listing with that pictures' users name with the same item the listing was buy it now for 15.95 + 6 shipping from hong kong.

thanks for your help

that works fine.

I can remove a 10vac leg and it works correctly
I can switch the 110 side of the transformer off via a strip surge protector and that works correctly
I can unplug/plug in/unplug etc the surge protector from the 110 source and that works correctly

It's only when I unplug/plug in/unplug the transformer from the 110 source that the arduino locks up

anyways - I found a 18vac doorbell transformer - and that doesn't lock up the arduino - so it's just has to be that other transformer - odd

I misspoke - I've got it connected to collector - and not the base.

I'll try see if I have a different ac wall wart in my junk pile

again thanks for your help

Your showing a 4N25 - and I'm using a 4N35 is there much of a difference?

correct the opto input side is not connected to the output (arduino) side in anyway.

I also plugged in a different 4N35 and also tried a 4N33

arduino side is
          +5v
base - 1kΩ - Digital Pin 4

like I said it works great except if I unplug the transformer multiple times - I get my different on/off states (shown below as 1 and 0) if I remove one of the 10vac lines or use a switch to power off the transformer

11111111111111000000001111111000111111111100011110001111

so I plugged the transformer into one of those cheap strip surge protectors - I used the switch on the surge protector to switch the transformer on and off - no issues.

but if I unplug the transformer from the strip with the power on it locks up

on the pins 4/5 on the 4n35 (to the arduino) - power off get 19MΩ and power on get .4kΩ  readings with arduino  pins not connected

with arduino pins connected get - power off .37KΩ and 5volts and power on 1.24KΩ and .5volts readings

ok added some comments to my code -
I think my issue is hardware and not software - but I'm often wrong

Code:

const int pin = 4;
unsigned long millisLastMin = 0;
unsigned long millisLast = 0;
const int pinOn = LOW;
unsigned long onSeconds = 0;
unsigned long onSecondsLast = 0;
int thisSecondOn = 0;
int pin60[60];
int pin60Pos = 0;

void setup(){
  pinMode(pin, INPUT);
  digitalWrite(pin,HIGH);
  Serial.begin(115200);
  Serial.println("Start");
 
}


void loop()
{
  int r = digitalRead(pin);
//if hasn't been on in this second check if on now
  if (thisSecondOn == 0) {
    if (r == pinOn) {  //do we have power
      Serial.print("+"); //debug comment only
      thisSecondOn = 1; //got power this second dont need to check again until next second
      onSeconds++; //add to power seconds on
    }
  }
//new second so reset so that we check during this second time period
  if (millis() - millisLast > 1000) {
    millisLast = millis();
    Serial.print(thisSecondOn); //debug comment only
    thisSecondOn = 0;

  }

//after a minute save our data
//byte for pin60[] would be better then int as should never be more then 60 for seconds in a minute - changed to int to make sure //not some overflow issue

  if (millis() - millisLastMin > 60000){
    millisLastMin = millis();
    Serial.println("x"); //debug comment

    //pin60Pos is our minutes in the hour
    pin60[pin60Pos++] = (onSeconds - onSecondsLast); //save our seconds for this minute into an array
   
// sum our hour
    int pin60Sum = 0;
    for (int x=0;x<60;x++)
    {
      pin60Sum +=pin60[x];
    }
    if (pin60Pos > 59) pin60Pos = 0;
    onSecondsLast = onSeconds;
   
    //output seconds on in the hour [Hh]
    //output total seconds on [Ht]

    Serial.print("[Hh]");
    Serial.print(pin60Sum);
    Serial.print("[Ht]");
    Serial.println(onSeconds);
  }
}

my cap's are in the basement so they will have to wait until later - but I moved declarations above setup and used const HIGH.

Same result.

Here's my serial output - as I expect until it locks up- the zero's are when I pull one leg of the 9vac output from the circuit - 1's are if line has power in that second.

It's only when I pull the transformer from the wall (i.e. 110vac), reinsert it, pull it out, reinsert that it locks up - so only when I'm doing that does it lock up.

Start
00000000000000+1+1+1+1+1+100+1+100+1+1+100+1+1+100+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+x
[Hh]38[Ht]38
1+1+1+1+10

another run:

Start
+1+1+1+1+1+1+1+1+1+1000+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+x
[Hh]57[Ht]57
1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+x
[Hh]117[Ht]117
1+1+1+1+1+1+1+1+1+1+1000000000000000000000000000+1+1+1+1+1+1+1+1+1+1+1+10000000000x
[Hh]139[Ht]139
000000000000000000000000000000000000000000000000000000000000x
[Hh]139[Ht]139
000000000000000+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+x
[Hh]185[Ht]185
1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+x
[Hh]245[Ht]245
1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+10000000000000000000+1+1000000000+1+100+10+100+10000x
[Hh]267[Ht]267
000