Tried to edit my post but was too slow, what I should have said is could you explain when I would need a resister on the emitter?

Also, would you mind telling me the circuit/sim software you are using?

Thanks again for the patience and help.

No resistor on the emitter required. If it were there, it would effectively be in-series with the relay coil, so might screw up the operation of the relay. Take ~90% of the stuff you read about electronics on the internet as crap, which it is. Newbies are much better at creating html than circuits.

LTSpice. Free download at www.linear.com

 

I tested it yesterday and again got mixed results. When it was just attached to the alarm power supply and the power to the doorbell power supply was off the alarm worked as planned - success! But when I plugged in the doorbell power supply, on button push the doorbell would ring but the alarm did not. This is a new problem that makes no sense to me.

I again thank you for all your time, I've decided to go back to my original design and use the second power supply, I know that will work.

 

Thanks to Mike, I found a solution that works, I must admit I don't fully understand why. Here is my circuit:



My understanding of this circuit is as follows:
When the doorbell is pushed the capacitor is charged and the base of the transistor is powered allowing the current to flow through the collector and emitter back to the alarm zone, thus closing the circuit and activating the alarm. When the button is released the capacitor discharges into the base, momentarily allowing the transistor to continue conducting. R2 and R3 deal with the non-stiff voltage coming from the alarm zone. R1 protects the push button and D1 blocks current from the doorbell controller.

A little history on how I got here:
1) Used above circuit with single resister connected to base - worked on breadboard, but not alarm zone
2) Assumed hooking direct to the alarm zone was an issue, modified circuit to use Vaux voltage from alarm - worked on breadboard, but not alarm zone
3) Assumed using transistor to create continuity in alarm zone was an issue so added relay after transistor - worked on breadboard, but not alarm zone, posted here.
4) Made changes recommended by Mike - worked on breadboard, but not alarm zone - posted here
5) Made changes recommend by Mike due to non-stiff voltage - worked on breadboard, worked on alarm zone when no voltage was present in the doorbell, did not work when doorbell voltage was added.
6) Went back to original design but added voltage divider resisters per Mike's non-stiff voltage suggestions. Tried different values of R2,R3 and C1 until I got it working on breadboard resulting in above circuit. Tested on alarm - IT WORKS 95% of the time! A really fast doorbell push will not activate the alarm.
7) Drew it up in Spice and tried to simulate it but I don't have a model for the Push Button and it errors there.

Next steps, I am going to continue experimenting with the values for R2,R3 and C1. My goal is to lower the time constant so the capacitor charges very quickly. Through testing I have found that a 1 second delay is not necessary for the alarm to register continuity so I am going to use progressively smaller capacitors until it stops working, my guess is I need .2 seconds. In my next test I am going to use 10K resistors and start with a 22u capacitor.

I want to again thank Mike, I would have never arrived here had it not been for his patience and help.

 

Well, just finished another test on the system. Settled on 12K for R2 and R3 and a 200u for C1 - this seemed to give the best results. Again mixed results while pushing the doorbell as fast as I can - with no doorbell power, alarm response was 100%; with doorbell powered, about 50%. I simply don't understand why having the doorbell powered would effect the response rate - the only difference in the circuit is that when the doorbell is powered there would be some current at S1 but it would be blocked by D1.

Any ideas would be appreciated.

 

I thought a functional diagram with specs/requirements might help you all help me so here goes:


Notes:

1) Doorbell is wired (T-568B) to Doorbell Controller via modified cat5 patch cable.
2) Only pins 2 (orange) and 6 (green) are drawn, remaining pins are straight through.
3) Alarm zone is set to Normally Open (NO).
4) D1 blocks circuit board/alarm current from doorbell controller while D2 blocks doorbell controller current from circuit board/alarm. Diodes are 1N4001.
5) Alarm power is rated at 12V/1.25A, but the voltage is not stiff.
6) Doorbell power supply is rated at 12V/500mA.
7) The doorbell button push will activate the alarm and doorbell with just the modified cat 5 cable IF the button is pushed slowly. When the button is pushed quickly, only the doorbell activates.
8) The requirement for the circuit is to extend the closure of the doorbell switch for approximately .25 seconds to insure the alarm is activated on a “fast” doorbell push.
9) If required the alarm could be changed to Normally Closed (NC).
10) If required continuous 12V power is available via Vaux (also not stiff).

Thanks in advance

 

Well I finally got it to work - yea!. Changed to a 555 monostable (straight from Platt's "Make: Electronics") to generate the pulse on doorbell push. With THE 100k resistor and 10u capacitor I get a delay of about 1.1 seconds. I conducted about 50 tests with a 100% success rate.



Note: I switched the alarm to Normally Closed (NC) (I figured it would be good to "precharge" the capacitors), thus the PNP transistor. I do have a couple of questions for those that are interested:

1) I put the LED and resistor in place for testing purposes - I would like to get rid of them, but when I just run a wire from the collector to ground it does not work - any ideas?
2) I think my resistors and capacitors are appropriate values but I can't get the push button model in Spice to work so I am unable to play around with different values - any suggested changes would be appreciated.

Thanks again for those that helped.

 

Well I finally got it to work - yea!. Changed to a 555 monostable (straight from Platt's "Make: Electronics") to generate the pulse on doorbell push. With THE 100k resistor and 10u capacitor I get a delay of about 1.1 seconds. I conducted about 50 tests with a 100% success rate.

View attachment 90741

Note: I switched the alarm to Normally Closed (NC) (I figured it would be good to "precharge" the capacitors), thus the PNP transistor. I do have a couple of questions for those that are interested:

1) I put the LED and resistor in place for testing purposes - I would like to get rid of them, but when I just run a wire from the collector to ground it does not work - any ideas?
2) I think my resistors and capacitors are appropriate values but I can't get the push button model in Spice to work so I am unable to play around with different values - any suggested changes would be appreciated.

Thanks again for those that helped.

If that timer circuit really worked, then the fastest the bell would ring is every 1.1 sec minimum. Is that what you want? What do you consider to be a fast, repeating, doorbell push? One press every 1/4 sec? 1/2 sec? 1 sec? or?

Do you have a schematic of the door bell controller? We need to see the door button input circuit.

 

If that timer circuit really worked,

The circuit works and the delay of 1.1 sec is what I need. Multiple doorbell pushes will be dealt with via my automation software interfaced with the Elk M1 Gold.

I do not have a schematic of the doorbell controller. But a previous post showed the functional diagram. It is connected to the doorbell via a modified cat5 cable. As shown, I am pulling the doorbell push off of wires 2 and 6. Per the functional diagram the controller circuit is protected from my alarm circuit via a 1N4001 diode on wire 6. It's power supply is rated at 12V/500mA. The 1N4001 on my circuit protects it from the controller current.

I was able to remove the LED and it's resister and successfully retested. I also found that I had C3 reverse biased on my spice model (but not on the actual breadboard). Below is the corrected circuit.



I did get the Spice simulator to run but only for 110ns; I get the following error "Analysis: Time step too small: time=1.14959e--007, timestep = 1.25e-019: Trouble with 1n4001-instance d1" I tried several changes to .tran to no avail? I will do some more spice research and try to fix this.

Before I solder this up I am still left with two questions:
1) Is R1 value of 220 appropriate to protect the push button?
3) Is R2 value of 10K appropriate to protect the PNP base?

Thanks again.

 

What is the "door bell trigger" input circuit?.

Perform these measurements with the trigger disconnected:
With the power off, measure the resistance (with volt/ohm meter) across the trigger input and ground. Reverse the leads and measure again. Post the results.

With power off, measure DC voltage across trigger and ground,reverse the leads and measure again. Post the results. Do the same with power on.

Indicate how the meter leads were connected for each measurement.

1meg resistor and 1uf cap should give about 1.1 second output pulse. Your circuit is not right.

 

What is the "door bell trigger" input circuit?.

Perform these measurements with the trigger disconnected:
With the power off, measure the resistance (with volt/ohm meter) across the trigger input and ground. Reverse the leads and measure again. Post the results.

With power on, measure DC voltage across trigger and ground,reverse the leads and measure again. Post the results.
Indicate how the meter leads were connected for each measurement.

1meg resistor and 1uf cap should give about 1.1 second output pulse. Your circuit is not right.

I'm not sure what you mean by "what is the door bell trigger input circuit?" As shown in the functional diagram it is a NO momentary push button that is wired via cat5 to the doorbell controller.

There is no resistance as it is a NO momentary push button switch. If measured with the switch activated its about .3 ohms (approximately 10' of cat5 wire), around 800K if I measure after the diode on the cat5.

Dc voltage is 12.1V when red on trigger and black on neg, -12.1v if reversed.

As shown, I am using a 100K resister and a 10uf cap, which gives me (tested many times) a 1.1 second pulse. Isn't that mathematically the same as 1M and 1 uf?

As a reminder my circuit is intended to "sense" the doorbell push to trigger an N/C alarm zone on my Elk alarm panel (I will use that alarm to initiate automation that will take a pic of the person at the door and text it to me) - the doorbell functioning (chime and intercom) is independently taken care of by the doorbell controller). Again I am using two diodes to block current from each circuit from entering the other.

Since I have bread boarded my circuit and tested it connected to my doorbell controller and Elk and it works perfectly; I'm not sure what's "not right" about it. I was just looking for verification on my switch resistor (which I inferred from a previous post by MikeML) and my base resistor which I calculated using a free online transistor resistor calculator.

I admit that I can't get it to run in Spice - I'm still trying to get it to work - looks like I may have to make a new post in the electronic resources forum to figure this out.

Thanks,

 

Mr Rat,
looking at the LTSpice schematic in post #28, you have a dead short from +12V to Gnd when Q1 turns on. Post your .asc file...

 

Mike,
Here you go, thanks in advance.

I originally had a LED/resistor between the two for testing. When the 555 pulses the base of the resistor, the circuit is open, which is what causes the NC alarm zone to "alarm."

Tom

 

Hi

Here is the circuit I had in mind.

The "Alarm" coil will change to something else. I'm trying to establish what the output circuit should be if you can tell me what its driving. That's the reason for the questions in my previous post.

 

Hi

Here is the circuit I had in mind.

The "Alarm" coil will change to something else. I'm trying to establish what the output circuit should be if you can tell me what its driving. That's the reason for the questions in my previous post.

The output is an open circuit - this causes the NC alarm zone to trigger. When the 555 out pulses the PNP it breaks the circuit.

 

Mike,
Here you go, thanks in advance.

Tom

Mike,

I just noticed that I have R1 (push button protection) on the negative leg of the switch, based on your previous postings it should be on the positive side?

Tom

 

OK...I understand what your attempting...

I would have the 555 drive an optocoupler as an interface to your alarm system.

 

OK...I understand what your attempting...

I would have the 555 drive an optocoupler as an interface to your alarm system.

OK, thanks for your help.

 

More info from the install manual..

1. Should place a 2.2k resistor acoss zone Z+ and Neg.
2. Open circuit should measure 13.8V
3. Non-violated circuit should be 7.0v
4. closed circuit should be 0.0v

Basically, when an open contact closes (a violation occurs), it places a short across the resistor.

The non-violated circuit voltage suggests there is an approx 2.2k zone input resistance. So optocoupler would need to accomodate a current requirement of about 6ma.

all a guess on my part of course..

 

More info from the install manual..

1. Should be a 2.2k resistor acoss zone Z+ and Neg.
2. Open circuit should measure 13.8V
3. Non-violated circuit should be 7.0v
4. closed circuit should be 0.0v

Basically, when an open contact closes (a violation occurs), it places a short across the resistor.

The non-violated circuit voltage suggests there is an approx 2.2k zone input resistance. So optocoupler would need to accomodate a current requirement of about 3ma.

all a guess on my part of course..

Wow, I really appreciate all the time you have put into this but I have a working circuit - I cannot get it to work in Spice, but it works perfectly in real life - there is no reason to add an optocoupler.

Per above, I am unsure of two resistance values I selected. Since I had R1 on the wrong side of the switch, I don't even think I need it since it is now in series with R5, I'm sure Mike will respond to that question, when he gets a chance. Since I'm a newb and used an "unknown" online tool to calculate R2, the PNP base resistor, I just wanted a sanity check on it before I solder up the final circuit, but I'm 99% sure it is the right value.

FYI, I am setting the zone as a Normally Closed Zone Def 13 which does not require the 2.2k EOL resister.

 

Wow, I really appreciate all the time you have put into this but I have a working circuit - I cannot get it to work in Spice, but it works perfectly in real life - there is no reason to add an optocoupler.

Per above, I am unsure of two resistance values I selected. Since I had R1 on the wrong side of the switch, I don't even think I need it since it is now in series with R5, I'm sure Mike will respond to that question, when he gets a chance. Since I'm a newb and used an "unknown" online tool to calculate R2, the PNP base resistor, I just wanted a sanity check on it before I solder up the final circuit, but I'm 99% sure it is the right value.

FYI, I am setting the zone as a Normally Closed Zone Def 13 which does not require the 2.2k EOL resister.

Ok...I 'm done..i won't spend anymore time

but...the manual shows a 2.2k resistor in series with a normally closed contact though...