Nc Reed Relay Not Triggering Alarm When Opening

[wbrells]

Hello!

I'm new to this forum, but I can't seem to find anyone with a problem similar to the one I am having. If this problem has already been addressed, I apologize!

I'm having an odd problem trying to modify a Skylink wireless door sensor so that it can be triggered via an external relay. The original door sensor contains an integrated magnetic reed relay which is normally kept closed with a magnet as usual. I've soldered wires to each end of the reed relay and connected those wires to the contacts of an external reed relay controlled by a simple relay driver circuit that I put together. The intent is to have the (modified) door sensor triggered by this external relay rather than by the original magnet. Indeed, if I manual connect the wires together and then separate them the alarm triggers. HOWEVER, when I connect those wires to the NC contacts of the external reed relay the alarm does NOT trigger when that relay is de-energized and the contacts OPEN! (Yes, I have verified that the contacts ARE opening!) Interestingly, the alarm DOES trigger when I disconnect the above-mentioned relay driver circuit from the power line! (It is powered via a small 12VDC power "cube" that is plugged into a wall socket.) I'm very perplexed by this behavior because there is no current (that I can measure, anyway) flowing through the relay coil before or after I unplug the power "cube"!

Would anyone have a suggestion as to what may be causing this really (to me, anyway) oddball behavior? BTW, I tried a different somewhat larger external relay - it is encapsulated so I'm not really sure what kind of relay it is - and got the same result...

Many thanks,

Wayne

[antinode]

How are you verifying that the contacts on the relay are opening properly?

My only guess is that when opening, the contacts are actually going very high resistance, which is not enough to trigger your transmitter. Try reading across thecontacts with a multimeter set to read resistance.

[luggsey]

If you put a wire either side of the reed "switch" then it will never go open?

You need to either destroy the reed "switch" or cut one leg off and join your wires in series with the reed switch.

[wbrells]

If you put a wire either side of the reed "switch" then it will never go open?

You need to either destroy the reed "switch" or cut one leg off and join your wires in series with the reed switch.

The internal magnetic reed switch is NO - it only closes when the magnet is nearby. It does not, therefore, seem necessary to physically remove that switch. HOWEVER, I did do the "experiment" of clipping the lead on one end of the switch. NO DIFFERENCE...

How are you verifying that the contacts on the relay are opening properly?

My only guess is that when opening, the contacts are actually going very high resistance, which is not enough to trigger your transmitter. Try reading across thecontacts with a multimeter set to read resistance.

I did use a multimeter to verify that the contacts are opening. The open resistance seems infinite (i.e. no meter movement on the highest resistance range) both with & without the power "cube" plugged in. Perhaps there is some coupling between the external relay coil & the relay contacts, but I find it hard to believe that this could be the cause of my problem...

[luggsey]

Ok, this switch works the opposite of most UK equipment, alarm is always open on standard door contacts.

It sounds like the contacts on your relay may not be "clean" or the signal from the wireless door sensor cannot be switched by the type of relay you have? How far are you trailing the wires?

[wbrells]

Ok, this switch works the opposite of most UK equipment, alarm is always open on standard door contacts.

It sounds like the contacts on your relay may not be "clean" or the signal from the wireless door sensor cannot be switched by the type of relay you have? How far are you trailing the wires?

I initially thought the relay might be "bad", but too different relays give the same result. Initially, the leads between the door sensor and my external relay were about 2 feet. As a test, I replaced that connection with a pair of 12" clip leads. No difference. BTW, I can also trigger the sensor by disconnecting either of the leads that connect the sensor to the external relay contacts. I thought the relay might be "chattering" a bit, but I have seen the same problem when running that relay off a battery rather than via the power "cube". Totally perplexing...

[james.wilson]

i dont fully get you. i think i see wha yur trying to do thoug.

any chnace of a circuit diagram?

[lawandorder]

i dont fully get you. i think i see wha yur trying to do thoug.

any chnace of a circuit diagram?

I'm not really sure that I understand the OP's objectives but it sounds to me like he has a wireless door conact which won't physically fit on the door so he wants to make the transmitter remote from the door so he can use a conventional contact.

If that is the case why the relay?

Why not simply wire directly from the door contact to the transmitter?

I'm not really sure that I understand the OP's objectives but it sounds to me like he has a wireless door conact which won't physically fit on the door so he wants to make the transmitter remote from the door so he can use a conventional contact.

If that is the case why the relay?

Why not simply wire directly from the door contact to the transmitter?

Having re-read the thread it seems that there must be some connection between the coil and the N/C contacts of the relay but you say you have tried two relays!

It does seem very strange and I can think of no logical explantion for it.

Do away with the relay, I don't understand why you are using it anyway. (unless I am missing something which, in fairness, is very likely)!

[hpotter]

This relay driver cct you put together, is it essentially a transistor with eg relay coil between emiter & 0v, (or collector & +ve) with biased base keeping relay energised?

If so, maybe transistor leakage, effectively short circuiting your contacts, is a possability.

(or maybe I'm just old, confused & hung over)

[wbrells]

i dont fully get you. i think i see wha yur trying to do thoug.

any chnace of a circuit diagram?

My goal - and the reason for the external relay, etc. - is to have a specialized sensor (part of a smoke detection system) trigger the SkyLink alarm system and/or an X-10 "Powerflash" unit. I'm just using a modified door sensor because it is the cheapest and most straight forward detector available for the SkyLink system.

My relay driver circuit is based on the one shown HERE that uses the 555 chip: http://www.jaycar.com.au/images_uploaded/relaydrv.pdf

As mentioned in the text of this article, the relay coil can be connected between pin 3 (output) and ground and that is the variation I'm using.

The output of the specialized sensor mentioned above is in the form of a variable resistance that ranges from about 3K (when the sensor is not triggered) to about 1Meg (when triggered). In my version of the above circuit the sensor is connected from the +12V bus to pins 2/6 of the 555. Those pins are then connected to ground via a 350K resistor. This setup seems to provide an appropriate "swing" for the triggering voltage so the 555 "flips" and the relay is activated when the sensor is triggered.

The 12V is supplied via a plug-in power "cube" which is "filtered" via a a 390 Ohm resistor an a 1000uF electrolytic capacitor. Finally, a 12V zener diode to used to stabilize the voltage.

I hope this description helps to clarify my setup!

This relay driver cct you put together, is it essentially a transistor with eg relay coil between emiter & 0v, (or collector & +ve) with biased base keeping relay energised?

If so, maybe transistor leakage, effectively short circuiting your contacts, is a possability.

(or maybe I'm just old, confused & hung over)

Originally, I was using this sort of circuit with a single NPN transistor and had the "no triggering" problem. I then switched to the 555-based circuit mentioned below, but the problem persists.

I am interested in your comment about transistor leakage. Can you be a little more specific as to how such leakage might affect the relay contacts?

Thanks!