Capacitor help please (vintage phone)

Other Hardware General Electronics
21

OE = Original Equipment.

The original setup has 2 wires connected to the capacitor on the OE box. I want to replace that box with a smaller capacitor.

You said

If you just want to ring the bell without it being
connected to a phone line or the other functionality of the phone then you need to generate about 75VAC at 25Hz and connect that to the bell.

So I took that to mean to connect the wires that would normally go to the OE capacitor to your recommendation.

The +/- wires from the ringer go to the Arduino to activate the ringer.

22

No, you need to build a circuit to generate 75VAC 25Hz.

Somewhere on here is such a circuit I posted years ago. Do some searching.

If you really can't find it I'll see if I can dig it out, but it is about 40 years old.

23

Ok, I see. Also, I know that the ringer runs at 60 Hz, will that male a difference?

24

Then you need to generate 60Hz. However that surprises me as I have 40+ years experience in the telecommunications industry and I've only ever known of bells that require around 20 to 25 Hz roughly. Are you sure it needs 60Hz?

25

I'm in the UK and it's getting late. If you haven't got a better answer by the weekend I'll see if I have something more helpful to offer you.

26

You're correct in the frequency. Not sure where I saw 60 at. Been looking at tons of sites and videos trying to figure this out.

27

The electro-mechanical bell clapper probably follows that frequency and it probably can't move at 60Hz.

28

You haven't said. Are you going to hook this up to a POTS telephone line? Where does the ring signal come from?

29

No phone line. Signal comes from the Arduino.

30

Okay, I'm just brainstorming now, so bear with me.
If I was gong to do this, I'd get a small step down transformer, say 115VAC to 9VAC and experiment with driving the secondary with a stepper motor driver at 25 Hz. What I would expect this to do is generate a 75-ish volt signal on the primary that you could use to ring the bell.

31

Sounds complicated, (but I love a challenge and to learn new things).

In the long run, space vs complexity, could I be better off just using the original equipment and using a relay between arduino and the OE box?

32

What does this mean exactly? You haven't said how you're going to generate the 75VAC from an Arduino.

33

I guess that's what I'm trying to figure out. :slight_smile:

I saw one guy replace the AC components with DC motors. I thought that would be too complicated, but it might be the better option.

34

Screen Shot 2023-02-16 at 5.32.36 PM

Something like this. You probably wouldn't need the capacitor.

35

So anybody else jump in with ideas. My Uncle AC (great name for an electrician, right?) demonstrated to me when I was 10 that you could get a shock from a transformer and a 6V lantern battery. I don't have a motor shield or I would try it. Probably just a MOSFET would work but I'm trying for something OP can actually build.

Edit: Actually you might be Abe to get a relay to chatter at 25Hz to drive the transformer.

36

I can add the following. The ring signal varied from country to country but they were all close. Don't hold me to this but pretty sure the exchange limited the ring current to 30 mA. Been plenty of years since growing up with rotary dial phones. Using an Arduino or similar uC I think you can drive a small transformer using an H Bridge.

Along the lines of EmilyJane's thinking a Google of "old telephone ringer using h bridge circuit" brings up a pile of circuits. Including a few multivibrator circuits driving a center tapped transformer.

Ron

37

That explains the capacitor value then. I wondered about that.

38

The capacitor was only there to block the DC component on the line. As a kid (1950s) more than once I got bit by a ring signal on the phone line. Had a fascination with telephone lines. :slight_smile: My guess is likely 15 mA would work fine so it's not like much current is needed. :slight_smile: Still have a few old rotary dial phones in the basement.

Ron

39

Perry, Emily, and Ron know what they're talking about, but I thought I'd just add that you can BUY "telephone ring generator modules" that will create the correct signal for you. They seem to be a bit pricy ($30 for this one), but by the time you start talking about motor drivers and step-up transformers, it might be an easier solution.

40

To make the ringer work you need 90 volts AC at about 30 Hz.