After a long and tedious war with this doorbell (current causalities: two dead arduinos, 1 dead relay and one dead optocoupler) I decided to stop trying to be too smart for my own good and do it in a way I can understand.

The bell has two circuits. one is 9v ac that comes from a transformer inside the wall. this goes through a rectifier and buck converter into the arduino (yes, I know the buck converter is not needed. However, it works and without it two arduinos died on me). Ringing the doorbell ground pin 3. The sketch then activate the relay that close the original circuit.

It is almost completely wire wrapped as I had to undo and redo the circuit so many times.

It is hosted inside a standard surface mount power/light switch box with blank plate.
As Marry Poppins said "A thing of beauty is a joy forever!"

Isn't it nice with everything covered?

Here is the sketch:

// Doorbell sensor
// to ring, ground pin 3. connect the relay that close the original circuit to pin 4
// 

#include <MySensor.h>
#include <SPI.h>
#include <Bounce2.h>

#define CHILD_ID 3
#define BUTTON_PIN  3  // Arduino Digital I/O pin for button/reed switch
#define RELAY_PIN  4  // Arduino Digital I/O pin bell relay

MySensor gw;
Bounce debouncer = Bounce(); 
int oldValue=-1;

// Change to V_LIGHT if you use S_LIGHT in presentation below
MyMessage msg(CHILD_ID,V_TRIPPED);

void setup()  
{  
  gw.begin();

 // Setup the button
  pinMode(BUTTON_PIN,INPUT);
  pinMode(RELAY_PIN,OUTPUT);
  // Activate internal pull-up
  digitalWrite(BUTTON_PIN,HIGH);
  
  // After setting up the button, setup debouncer
  debouncer.attach(BUTTON_PIN);
  debouncer.interval(5);
  
  // Register binary input sensor to gw (they will be created as child devices)
  // You can use S_DOOR, S_MOTION or S_LIGHT here depending on your usage. 
  // If S_LIGHT is used, remember to update variable type you send in. See "msg" above.
  gw.present(CHILD_ID, S_DOOR);  
}


//  Check if digital input has changed and send in new value
void loop() 
{
  debouncer.update();
  // Get the update value
  int value = debouncer.read();
 
  if (value != oldValue) {
     // Send in the new value
     Serial.println(value);
     gw.send(msg.set(value==HIGH ? 0 : 1));
     if (value == 0) {
     	Serial.println("activating rely for 1 sec");
     	digitalWrite(RELAY_PIN, HIGH);
     	delay(1000);
     	digitalWrite(RELAY_PIN, LOW);
     }
     oldValue = value;
  }
} 

Please feel free to comment - I am actually a bit disappointed that I didn't manage to do this the "right way" but it seems that the doorbell circuit is not "real" dc but half rectified AC. This is just a guess - I don't have the equipment to check this . As such it destroys components nicely, especially mechanical relays....
The downside of doing it this way is that the doorbell will not ring if the arduino dies. well, they can always knock, can't they?

First, special thanks to @Chester for thinking the way to do that and @Sparkman, my hero, for correcting my silly mistake.

These sensors are for checking if the kids (or me, just hypothetically ) left the air conditioning running in their rooms. What makes it work is that the flaps move in a particular way when you turn the air conditioning off in my wall unit and they "close down" to a position that is impossible while its running.
This is the sensor (looks almost professional!):

I have since added also battery monitoring although I have to tweak it a bit as it shows 66%.
The reed sensor sense the presence of a magnet on the flap.

This is the sensor in position. Couldn't find my kids blue tack so had to use blue tape.

I have carefully measure everything to fit into one of the super cheap aliexpress project boxes. what I didn't take into account was that the battery adds extra 4mm to the height. Darn.

Here you can see the magnet:

and this is the sketch:

#include <MySensor.h>
#include <SPI.h>

#define REED_PIN 3
#define INTERRUPT REED_PIN-2 // Usually the interrupt = pin -2 (on uno/nano anyway)
#define CHILD_ID 1
#define SLEEP_TIME 28800000
int BATTERY_SENSE_PIN = A0;  // select the input pin for the battery sense point




MySensor gw;
MyMessage msg(CHILD_ID, V_LIGHT);

 
void setup() {
  
  analogReference(INTERNAL);

  pinMode(REED_PIN, INPUT); 
  digitalWrite(REED_PIN, HIGH); //internal pullup
//  pinMode(A0, INPUT); 
  Serial.begin(115200);

  gw.begin();
  
  gw.sendSketchInfo("AirCon Sensor", "1.0");
  gw.present(CHILD_ID, S_LIGHT);
  
}

int old_value = -1;
int oldBatteryPcnt = 0;


void loop() {
	int value;  
	int bValue;
  
  // Listen for any knock at all.
  
///  gw.process(); // Process incomming messages
  
//  	t = analogRead(A0);
  	value = digitalRead(REED_PIN);
  	
	Serial.println(value);
  	delay(500); //debounce
  	if (value != old_value){
  		old_value = value;
  		gw.send(msg.set(value));
  	}

	//Battery
	bValue = analogRead(BATTERY_SENSE_PIN);
    int batteryPcnt = bValue / 10;
    Serial.print("Battery : ");
	Serial.print(batteryPcnt);
	Serial.println("%");
	if (oldBatteryPcnt != batteryPcnt) {
    	gw.sendBatteryLevel(batteryPcnt);
    	oldBatteryPcnt = batteryPcnt;
	}

	gw.sleep(INTERRUPT,CHANGE, SLEEP_TIME);
 
} 

And here they are, mounted properly:

Simple sensor using http://www.aliexpress.com/item/1pc-lot-SW-420-Normally-Closed-Alarm-Vibration-Sensor-Module-Vibration-Switch-30512/32259757483.html. the sensor is attached to the top of the machine with one of those sticky dots. I found out it achieves the best and most accurate readings this way. (http://www.aliexpress.com/item/100pcs-lot-Balloon-attachment-glue-dot-attach-balloons-to-ceiling-or-wall-Globo-paste/2029756655.html)

The sketch is a bit messy and probably could use a little love and constants but it works for me.
The basic logic is:

1. check for vibrations every 100ms
2. if vibrations were detected, mark the period as "vibration" (a period is 5 minutes)
3. if there was a vibration period after long period of quiet report "start of cycle"
   4 if there was a longish period of quite after a vibration period, report "end of cycle"
4. in domoticz the change of state trigger a hangouts message to me.

the sketch was tested on almost all cycles in my machine. It might fail if i load the machine late at night for early morning start as the opening and closing of the door might be detected as false positive. i might add a big red reset button to clear the state if it bothers me too much.

here is the sketch:

// Sensor to detect washing machine end of cycle
// Connect vibration sensor to digital pin 3 


#include <MySensor.h>
#include <SPI.h>


#define CHILD_ID 3
#define BUTTON_PIN  3  // Arduino Digital I/O pin for vibration sensor
#define SAMPLING_PERIOD 300000 // 5 minutes period. YMMV
MySensor gw;
int oldValue=-1;
unsigned long period_start = millis();
int state = -1;


MyMessage msg(CHILD_ID,V_TRIPPED);


void setup()  
{  
  gw.begin();

 // Setup the button
  pinMode(BUTTON_PIN,INPUT);  
  // Activate internal pull-up
  digitalWrite(BUTTON_PIN,HIGH);
  
  gw.present(CHILD_ID, S_DOOR);  
}

void report_state(int state)
{
	  	Serial.print("reporting state: ");
		Serial.println(state); 
	    gw.send(msg.set(state));
	
}

int prev_state = -1;
int prev_state_length = 0;

//  Check if digital input has changed and send in new value
void loop() 
{
  // Get the update value
  int value = digitalRead(BUTTON_PIN);

  if (value != 0 && state != 1) { // vibration detected for the first time during the period
  	state = 1; 
  }

  if (millis() - period_start > SAMPLING_PERIOD) {
  	period_start = millis();
  	Serial.println(state);
    if (state != prev_state) {
  		if (state == 1 && prev_state_length > 4) { //a vibration period after long period of quiet means a cycle started
  	    	report_state(state);
	    	prev_state_length = 1;
  		
  		} 
  	} else if (state == 0 && prev_state_length > 2) { // a long period of quiet means cycle ended
  		if (prev_state_length == 3)
  			report_state(state); // report only once 
  	}
  	
  	if (state != prev_state)
  		prev_state_length = 1;
  	else
  		prev_state_length++;
	prev_state = state;
    state = 0;
  	
  }
  
 
  delay(100);
} 

@Didi it is cheaper to buy better fire and life insurance

Following this instructable, I decided to invest 3$ in a 1000 in 1 remote (http://www.aliexpress.com/item/Lowest-profit-Universal-LCD-Display-AC-Remote-Control-Controller-For-Air-Conditioner-Conditioning-1000-in-1/1980863274.html)

I ordered two kinds but this one was much better then the other one (i.e it worked )

Soldering to the copper lines the way the kid did in the instructable proved to be problematic (at least for me) and I ended up soldering to the contacts of the pressure sensitive pads. At first I thought to use it without LCD but ended up with it as otherwise I don't know what is the current setting.

It actually work!!! I can turn my AC on and off!!! a dream comes true!!!
However, turning it on will bring it to one preset. this is not too bad - I actually want only to heat the bedrooms before kids go there and turn off the ac that they left on....

Here is a nude photo:

I know there are some sharp eyed people in this forum, so yes, in the photo the remote is just powered by the arduino, i tested first by giving the transistor 5v manually.
I have ordered 4 more of this remote and will do a cleaner work on the soldering

whoever tells you integration will be seamless is trying to sell you something
I believe that it will be seamless only with their sensors/actuators... I had ninjablock, which is similar (not that much, as its supposed to use generic 433mhz devices) and is now a pile of junk as they basically dropped support of it to move to their other project. never again! the beauty of mysensors is that you are not bound to any HA software, or any sensors maker. and you have full control of what your sensors are doing and how they are doing it. yes, we are control freaks

assuming an rpi will act as the sensor backend, would it be possible to send it on the rf module and the current mysensors protocol? this would definitely bring the price and power consumption up but can still be an interesting idea IMHO.

@tbowmo another option is mysensorized egg timer. mount it on some base with rotary encoder. turn with visual response to set timer. count down will turn off led by led and alarm will also trigger event in HA

@Qu3Uk You are right... yes, they should have charged a small monthly fee... I really liked my Ninja other than the fact that it was cloud based and I always felt a bit reluctant to let the cloud reach into my network. Also 433mhz is problematic.
It is funny how many bright ideas goes into the rubbish bin because of people who can't do the math
I use domoticz. I tried openHAB and another 2 that I can't remember - they were all very hard to set up - openhab has a challenging learning curve, and that's an understatement

@AWI Darn you are right!!!!! Thanks! Have been dealing with rpi and upwards lately so assumed it has some kind of internal clock.
Thanks again!

@AWI as it should.... but - it should show a very long number.... not a 4 digit one. and not the same values each time i run the code.

this is a test code, just to show the problem. in the original code there was static var, etc and the difference was checked.

It has been a long time but i am back... however, I must have lost it!

Millis now return 4 digits results and I can find the reason. It might be the update of the libraries the arduino IDE asked me to do. Anyways, here is the code:

#define MY_DEBUG
#define MY_RADIO_NRF24

#include <SPI.h>
#include <MySensors.h>                       // Mysensor network

void setup() {
  // put your setup code here, to run once:

}

void loop() {
    unsigned long now;

    Serial.println("entering loop");
    now=millis();
    Serial.print("now=");
    Serial.println((unsigned long)now);
      sleep(5000);


}

couldn't be simpler....

now the result:

x00
x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x000 MCO:BGN:INIT NODE,CP=RNNNA--,VER=2.1.1
3 TSM:INIT
4 TSF:WUR:MS=0
11 TSM:INIT:TSP OK
13 TSF:SID:OK,ID=28
14 TSM:FPAR
33 TSF:MSG:SEND,28-28-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
272 TSF:MSG:READ,0-0-28,s=255,c=3,t=8,pt=1,l=1,sg=0:0
277 TSF:MSG:FPAR OK,ID=0,D=1
2040 TSM:FPAR:OK
2041 TSM:ID
2042 TSM:ID:OK
2044 TSM:UPL
2046 TSF:MSG:SEND,28-28-0-0,s=255,c=3,t=24,pt=1,l=1,sg=0,ft=0,st=OK:1
2054 TSF:MSG:READ,0-0-28,s=255,c=3,t=25,pt=1,l=1,sg=0:1
2059 TSF:MSG:PONG RECV,HP=1
2061 TSM:UPL:OK
2063 TSM:READY:ID=28,PAR=0,DIS=1
2067 TSF:MSG:SEND,28-28-0-0,s=255,c=3,t=15,pt=6,l=2,sg=0,ft=0,st=OK:0100
2073 TSF:MSG:READ,0-0-28,s=255,c=3,t=15,pt=6,l=2,sg=0:0100
2080 TSF:MSG:SEND,28-28-0-0,s=255,c=0,t=17,pt=0,l=5,sg=0,ft=0,st=OK:2.1.1
2088 TSF:MSG:SEND,28-28-0-0,s=255,c=3,t=6,pt=1,l=1,sg=0,ft=0,st=OK:0
2095 TSF:MSG:READ,0-0-28,s=255,c=3,t=6,pt=0,l=1,sg=0:M
2100 MCO:REG:REQ
2103 TSF:MSG:SEND,28-28-0-0,s=255,c=3,t=26,pt=1,l=1,sg=0,ft=0,st=OK:2
2109 TSF:MSG:READ,0-0-28,s=255,c=3,t=27,pt=1,l=1,sg=0:1
2114 MCO:PIM:NODE REG=1
2116 MCO:BGN:STP
2118 MCO:BGN:INIT OK,TSP=1
entering loop
now=2120
2121 MCO:SLP:MS=5000,SMS=0,I1=255,M1=255,I2=255,M2=255
2127 MCO:SLP:TPD
2129 MCO:SLP:WUP=-1
entering loop
now=2131
2131 MCO:SLP:MS=5000,SMS=0,I1=255,M1=255,I2=255,M2=255
2138 MCO:SLP:TPD
2140 MCO:SLP:WUP=-1
entering loop
now=2142
2142 MCO:SLP:MS=5000,SMS=0,I1=255,M1=255,I2=255,M2=255
2148 MCO:SLP:TPD

I have been staring at this for the last two hours... Any help will be appreciated. I am sure it is something ultra stupid

Regards,
Moshe

@JahFyahh it was mostly trial and error. I was lucky and my initial setup was good but these sensors have very sensitive adjustment (all cheap sensors do, i think) and sometimes a fraction of a turn is enough to change things. I think I wrote a simple "read in a loop" sketch and shaked it a bit (like a washing machine, small shakes) to see if i have a read. Hope that helps. I think top of the machine vibrates a bit more than back. if you put on the back, maybe try to mount it high as the upper part moves more than the lower part.

@JahFyahh yes, still using it. I never get false readings although lately I started getting the notifications half way through the cycle. Need to check the glue.

@chuckconnors I seriously doubt that. the washing machine has much move violent movements. For the dryer I think I would go with current as it is continuously drawing current (lots of current!) while working. In retrospect I would do the same with the washing machine if it was not under warranty. get a small junction box, expose about 3cm of the cable and use non invasive current sensor, all inside the box. Problem is, as always, power for the arduino.
another option that I considered is taking a good quality power strip, with lots of space in it and putting the sensor and the arduino inside it or only the current sensor (as the wires are exposed usually inside the strip) and the arduino device and charger on the outside. many modern strips have good quality USB sockets so no need for charger.
just my 2c... not saying you should touch mains, etc bla bla bla....

@petewill My original plan was to unintrusively detect the ring and trigger the arduino without effecting the bell circuit. However, it proved to be a bit more complicated and 2 dead arduinos and several other fried components later I gave up.

@petewill ummmm you could still cut the ring even if it was the other way around with a relay. Sorry to be a pain can't fight my mold hehehe. generally I find the reliability of dorrbells (especially the old wired kind) to be excellent. mine has been working flawlessly for at least 35 years.

Hello all - sorry I have been away for so long...
This bring back memories http://forum.mysensors.org/topic/1620/mysensored-doorbell
I wish I found a way of triggering the notification from the ring and not the other way around, as this way when something happen to your arduino the doorbell will not ring. Didn't happen yet - it works perfectly for 6 months but I would feel more relaxed if it was the other way around. Oh well...

@Cliff-Karlsson sorry for the delayed reply.
It needs to be set just on the verge.... So, turn it slowly until it is 0,give it slight turn back. These sensors do not have good signal amplification (its ok for the price i guess) so they work in a vwry narrow ranfe