I am trying to use my ethernet-connected arduino to operate two switches in my intercom so that I can open my frontdoor via the internet. One of the switches is a simple pushbutton switch so it is clear where the transistor should be placed.
The other switch however, is a vague switch which I can only see has 8 soldered pins sticking out on the back of the intercom's circuit board. The switch, which has a spring in it, is lifted when the intercom's receiver is picked up, and pressed back in again when the receiver is put back in its place, so the switch is either permanently on unless receiver is picked up or it is permanently off unless receiver is picked up.
I want to find out what two pins on the circuit board underneath the switch are connected/deconnected whenever the receiver is picked up, and I want to know the amount of voltage running through them so that I know what transistor to pick. The intercom is however plugged in and I have not yet been able to deconnect the power. Is there a way using the multimeter to check all possible pin pairs for current without possibly shortcircuiting them while the intercom is still on?
All transistors are good for at least 60V. It is unlikely that an intercom will use more than that.
You can not measure continuity on a live circuit with a meter because the meter itself pushes current between the two probes to measure it and any power in the circuit will at the least make any measurement useless and at the worst will fry your meter.
Measure voltages, and two points with the same voltage could be considered to be joined, but there is no guarantee of this.
Grumpy_Mike:
All transistors are good for at least 60V.
There are many transistors that are not rated at 60V or above.
Please provide links to these transistors. One will do for a start.
Grumpy_Mike:
Please provide links to these transistors. One will do for a start.
BC5458B.
I agree any transistor you come across is very likely to have sufficient voltage rating for connecting to the intercom. Anyway I would recommend using a relay such as this to keep the Arduino completely isolated from the door-entry electronics (need to check current rating is sufficient). If a transistor is to be used, it is important to check the voltages on the door-entry system with respect to earth.
Nedervino:
I am trying to use my ethernet-connected arduino to operate two switches in my intercom so that I can open my frontdoor via the internet. One of the switches is a simple pushbutton switch so it is clear where the transistor should be placed.
The other switch however, is a vague switch which I can only see has 8 soldered pins sticking out on the back of the intercom's circuit board. The switch, which has a spring in it, is lifted when the intercom's receiver is picked up, and pressed back in again when the receiver is put back in its place, so the switch is either permanently on unless receiver is picked up or it is permanently off unless receiver is picked up
I guess the 'hook' switch which seems to have 8 contacts is switching audio and the sounder. Why are you considering connecting to this switch when you have the simple pushbutton switch available?
The receiver needs to be picked up before you can open the door with the pushbutton switch, probably a safety feature for preventing accidental opening of the door. So I will need to be able to control both switches before I can open the door
Nedervino:
The receiver needs to be picked up before you can open the door with the pushbutton switch, probably a safety feature for preventing accidental opening of the door. So I will need to be able to control both switches before I can open the door
There's no easy way to work out what those 8 soldered pins do. You can try some detective work measuring voltages on those 8 pins with and without the handset lifted. Don't try to measure amps or ohms.
Can you find the signal that is sent to open the door?
Especially if the door-entry system is used by other apartments, make sure you don't short anything while taking measurements!
You mention using a transistor but I suggest you use a reed relay so as to maintain electrical isolation between your Arduino and the door-entry system. You can get them with a 5 volt coil that draws only 10mA, so can be connected directly to an Arduino output pin.
We had a landlord who refused to give each occupant a key. I found myself stuck inside without a key, unable to go out for 3 days until another occupants returned, knowing that I would be unable to get back in again. I investigated the door entry system and bent the normally-closed contact of a buzzer so it became a normally-open relay and connected that so it opened the lock. So pressing the door bell button opened the door! As the landlord was so unpleasant we left it like that when we left.