From Grumpy Mike's reply to the old thread, it seems it would be possible to power the electromagnet in an old phone ringer using a step-down transformer (110V-24V), an H-Bridge and some transistors.
In my case I would be replacing the 9V battery with the output of the transformer, and the motor would be the electromagnet in the phone. Does this seem correct?
My other question involves overall power for this project. I'd like to use the 24V from the wall to power the ringer and the Arduino if possible, but I'm not sure what sort of circuitry could accomplish this. I'd rather not rely on a battery for an extended period of time for the Arduino. I would imagine a voltage divider of some kind would be involved but I'd like to be sure (and safe). Any thoughts on that?
In my case I would be replacing the 9V battery with the output of the transformer, and the motor would be the electromagnet in the phone. Does this seem correct?
No.
You replace the motor with the transformer and your 9V battery with a wall power supply.
If you want to do what you said then you need the H-bridge to run at 48V.
I'd like to use the 24V from the wall to power the ringer and the Arduino if possible,
You can use it but you have to step it up enough to ring the bell.
CrossRoads:
Well, 48VAC to DC via bridge rectifier, smoothing caps, 5V linear regulator as the current for 5V will be quite low, yes?
No it is the other way round. He wants to ring a phone on stage or similar from an arduino. I used to do this sort of things in the 70s. In fact I met my wife doing the lights and effects for a neighboring amateur dramatics society.
A phone will ring if it receives 50-ish AC volts on its line.
More recent phones might require an exact frequency or else they might refuse to ring.
In rest there will be 48 volts DC, if the receiver is picked off hook it will drop to some 6 volts.
Speech will be superimposed on these 6 volts.
Dialing a number is going on / off hook within a certain time, so the voltage will change between 6 and 48 volts.
Often, after a call is answered (the other side picks up the phone), line polarity is reversed.
There's a lot of modes one can think of to use with a 2 wire line, and ancient phones use quite a lot of those modes.
A bit more info about the project: only the ringer will be used, the rest of the functions will be simulated using an audio shield and Arduino.
Grumpy_Mike:
You replace the motor with the transformer and your 9V battery with a wall power supply.
If you want to do what you said then you need the H-bridge to run at 48V.
Ok. I think I understand, except now I don't know what kind of transformer to use. I had found one that plugs into the wall and so the secondary voltage comes more or less out of the wall. From the above it seems I need one that converts the voltage closer to the other components. And so the signal to drive the phone ringer would come off of two other pins on the H-Bridge, yes?
There are battery-powered ring generator modules that might do the job. 12VDC battery to 70 V RMS @ 20Hz.
My concern with batteries is how long they could be expected to run without dying. This phone will ideally be installed in a gallery and left to run by itself for extended periods of hours/days/weeks. While this ring generator is simple and within my limited electronics skills, I'm not sure it's ideal. Any thoughts on if the above module have some advantages to wall power?
I had found one that plugs into the wall and so the secondary voltage comes more or less out of the wall.
No that is not a transformer that is a power supply. They can include a transformer in them but only as a component and nowadays they generally do not have one.
Use a 240V to 24V transformer like this:-
Grumpy_Mike:
No that is not a transformer that is a power supply. They can include a transformer in them but only as a component and nowadays they generally do not have one.
Use a 240V to 24V transformer like this:- Vigortronix VTX-126-006-612 Chassis Mains Transformer 6VA 2x 0-12V | Rapid Online
Although there are lots to choose from.
Okay, that makes more sense.
I'm wondering if this is a better potential solution that the self-contained ring generator that I posted above. Using power from the wall would be more reliable over time than a battery, but the ring generator is more simple from an electronics point of view. Also, I'd like to conceal all of the components inside the phone chassis, after removing the network terminal, so component size is yet another factor.
Might be easier to modify the guts of the phone bell to be directly ringable with 12v or similar. Or maybe just put a speaker in the phone and play the sound of a phone ringing.
From Grumpy Mike's reply to the old thread, it seems it would be possible to power the electromagnet in an old phone ringer using a step-down transformer (110V-24V), an H-Bridge and some transistors.
In my case I would be replacing the 9V battery with the output of the transformer, and the motor would be the electromagnet in the phone. Does this seem correct?
An "old fashioned" phone like a Western Electric Model 500 uses 90 volts AC at 20 hz. to ring.
As far as I can gather, the 90V is used so that the voltage can be preserved over long distances. For a short distance of just a few feet, I've read that a smaller voltage will do the job. However, 24V might still be too low.
zoomkat:
Might be easier to modify the guts of the phone bell to be directly ringable with 12v or similar. Or maybe just put a speaker in the phone and play the sound of a phone ringing.
I think I agree with this, and I'm likely going to pursue the ring generator option at first. Hopefully a speaker will not be necessary. Again my concern with the ring generator would be battery life, since driving the electromagnet requires a good amount of current.
The standard telco ring voltage is 90 volts peak to peak, but it's centered on a -48vdc 'resting' value. But as the ringer usually uses a series coupling capacitor, pure AC can be used if you just wish to ring the ringer.
I recall as a youth once touching both wires of the phone pair when an incoming call started ringing and it sure got my attention and was quite painful.
Lefty
This phone will ideally be installed in a gallery, and left to run on its own. Having enough power to run the ringer (assuming it rings ~30 times/hour for 2 seconds) is very important. The device I referenced above requires 12VDC, which can be received from a battery. However, I'd prefer to not have to change the battery every few hours, if the circuit requires a lot of current. Data sheets on these things are scarce, if they exist at all.
Here's what I'm asking: is it best to power this thing through a battery and assume that the batteries will need to be changed every so often, or is there some other way to provide 12VDC (converted from the wall, rechargeable battery) that I'm not thinking of? Is there a way I could calculate the estimated battery life of such a circuit?
Yes 12V power supplies are very common.
Just Google:-
12V power supplies
for lots and lots of them.
Is there a way I could calculate the estimated battery life of such a circuit?
Yes batteries will have a rating in milli amp hours, say 1200mAH, so very roughly the time will be 1 Hour if the drain is 1200mA or two hours if it is half that an so on. In fact the life is not quite as good as that so multiply any time by about 0.6 to get a more realistic powering time.
