Old telephone ringer stompbox

[GibsonGM]

This is a process that builds on itself, Sene.  One of the most useful little books I got when I started was about the 555 timer, by Forrest Mimms, from the old Radio Shack.  It shows how to configure the chip to do ALL kinds of things, your application included. You may find it online!

What Antonis is suggesting seems to be that the 555 cannot 'source' a ton of current (200mA?)...source meaning, to output it thru its circuitry.   What we do then is use a transistor to control the flow of current to the device (your bell), and the 555 is simply 'telling' the transistor how much current to release.....very much like your hand turning a valve to control the flow of water.   The actual power supply MUST be able to provide sufficient current to run the load, of course.  Even if  you had to place 2 9V batteries in PARALLEL with each other to obtain more ampacity (ability to source current).  + to +, - to -.


See this and look up other items related to "555 transistor drive load) for more!   https://www.youtube.com/watch?v=wk5AmxGoFAI

[GibsonGM]

Very first thing, I would determine if the 555 is doing what you built it to do.  Test it.  2/3 supply voltage on the output upon discharge (that's what you get from them, so only 6V if running on 9V...might be a hint).  Using an LED and CLR to see the output might help also.
I make these w/a pot so I can 'slow things down' a lot and see the output changing (like, 1Hz or less).

I like the transistor idea.

[antonis]

What Sir Mike said.. 

[SeneX225]

Very first thing, I would determine if the 555 is doing what you built it to do.  Test it.  2/3 supply voltage on the output upon discharge (that's what you get from them, so only 6V if running on 9V...might be a hint).

Test result is thus: between ground on the jack and the output the multimeter shows zero, so I guess it is indeed my bad wiring or soldering. I'll recheck everything until I get at least something on the output.

This is a process that builds on itself, Sene.  One of the most useful little books I got when I started was about the 555 timer, by Forrest Mimms, from the old Radio Shack.  It shows how to configure the chip to do ALL kinds of things, your application included. You may find it online!

See this and look up other items related to "555 transistor drive load) for more!   https://www.youtube.com/watch?v=wk5AmxGoFAI

Thank you for the reading suggestions. Microchips aren't exactly what I want to do going forward (although who knows, right?), but I'm sure there's stuff that will be useful nonetheless.

[GibsonGM]

Yes, I agree, going into microchips is a separate issue - 555 is an 'integrated circuit' and very common and useful for stompboxes...I only meant that you can find MANY websites and books about how to set up a 555 to do MANY different things.   Your application here is quite standard.

To test it for output, take an LED and something like a 470R resistor....anode ("+") of LED to pin 3 of the 555, cathode to the 470R, to ground.   When the 555 is running, it will make the LED flash - if it is set to a low frequency you will see 'discrete flashes'...if set to a high frequency, you may only see the LED glow, but it shows the presence of output voltage.     So, if you set the 555 up to be adjustable from 1Hz or so to the design frequency, you can set it low to see output and then adjust it faster for your project.  Hope that makes sense. 

A search for "LM555 astable design" will show many ways to do this, with calculators to give you the R and C values you need!   This is a classic 555 with relay kind of problem.  (the ringer is much like a relay)

Once you are assured that you have the astable output, LED flashing say 1x per second, you can try the ringer.   If it will not trigger, you may need to add the transistor circuit that Antonis showed.   The 'transformer' at the collector in the picture is the coil of the ringer. Don't forget to place a reversed diode as shown to protect the transistor; most all coils require this.   Once you do this a couple of times, it will not seem difficult      

[SeneX225]

Thank you, I'll try everything you've suggested as soon as I can and get back with whatever will happen.

A search for "LM555 astable design" will show many ways to do this, with calculators to give you the R and C values you need!   This is a classic 555 with relay kind of problem.  (the ringer is much like a relay)

Side note: Does type of the 555 matter? You referred to LM555, but I've got NE555. Could that cause any problems?

[GibsonGM]

Nah...my saying "LM" vs. your "NE" is just the manufacturer; it's a bad old habit from my  youth, LOL.  I recall that way back in the 90s, you got more search results if you expressed it that way - it's really just "555 timer IC".    The only diff you would really find with them is the CMOS version which would still do what we want here.   

[SeneX225]

Update:

Nothing good to report, unfortunately. I've remade the timer a bunch of times from scrap and not a single time did it work. Did I tell you I'm bad at this? 'cause I am.

I even caved in and bought that arduino oscillator I mentioned before:

While searching on how to make a 555 oscillator, I found this at the same local radioshack:



It's some Arduino module and has DC 5-15V with 1Hz-200kHz frequency. Will it suffice for this particular project?

I does what it says on the tin, so I actually get that oscillating signal as indicated by build-in LED. However, the bell still rings only once, like it did with direct DC input, and stays in one position on the bell it rung.

I am as confused as ever. I'm not giving up on building the timer myself, mind, but the fact that the pre-built one doesn't work either concerns me.

[GibsonGM]

Offhand with little coffee here yet, I would return to the idea that the arduino cannot source enough current to drive the coil.  You would need a transistor to act like a 'booster' for it.       Look at Reply #21 above, again.

[SeneX225]

You would need a transistor to act like a 'booster' for it.       Look at Reply #21 above, again.

I did, more thoughtfully this time, and saw what I got wrong. Previously I thought "not enough current" could be solved by adding more current into input, namely by using another (12V 3,3A) power supply. It, of course, didn't work.

Now, having also re-watched the video you linked a number of times I decided that I could just replicate that setup (which, retrospectively, I should've done first time around instead of fumbling an attempt to make one on my own).

I did just that but, sadly, it doesn't work, even without the transistor part. Potentiometer is different type from the one in the video, but it's a 100k.

Maybe you can spot something I'm missing?

[GibsonGM]

Need a schematic of the exact 555 circuit you're trying to build for it, Sene.   

You didn't 'add more current' into it - EVERY circuit draws current, you can't really push it in A circuit draws current as a consequence of how it is 'wired up'.   You applied 12V with the ability to deliver 3.3A (called "ampacity").  If the circuit WANTED to draw that much current, it could. It would only do so under conditions of bad error, however.  So it would burn itself up - the parts it is made of cannot withstand that high current.   Don't worry about that right now.

Is the LED oriented properly, with its cathode to ground?  Is the chip right way up (index mark 'up' in that pic?) hard to see, it's very dark.   Voltage present between pins 8 and 1?   I see NO timing cap in there at all...which are generally required for this timer to work.    Stick with it, you'll 'get it' over some time getting the LED circuit working! 

[SeneX225]

You didn't 'add more current' into it - EVERY circuit draws current, you can't really push it in A circuit draws current as a consequence of how it is 'wired up'.   You applied 12V with the ability to deliver 3.3A (called "ampacity").  If the circuit WANTED to draw that much current, it could. It would only do so under conditions of bad error, however.  So it would burn itself up - the parts it is made of cannot withstand that high current.   Don't worry about that right now.

That's a very clear explanation, thank you!

Need a schematic of the exact 555 circuit you're trying to build for it, Sene.   

Is the LED oriented properly, with its cathode to ground?  Is the chip right way up (index mark 'up' in that pic?) hard to see, it's very dark.   Voltage present between pins 8 and 1?   I see NO timing cap in there at all...which are generally required for this timer to work.    Stick with it, you'll 'get it' over some time getting the LED circuit working!

The video you linked didn't have any schematic, so I just tried to replicate the circut by following explanations. Everything seemed in order, but it still didn't work. However, I decided to dig a little deeper and found this video on the same channel. Seemed like something right up my alley!

To surprise of none but myself, this one worked. Next, I've added the transistor driver from the first video and connected whole thing to my ringer. Unfortunately, while the timer itself still works, the bell doesn't ring even once.



Couple things of note:
- Author in the video used an NPN transistor and a diode with no specifications, so I used whatever was lying around, namely 1N5818 and 2N3904. Maybe this (or any other component) needs to be more fitting?
- I've tried running the circuit with both shared and separate supplies for the timer and the ringer, but neither setup worked.

[duck_arse]

can you please show a photo of the coil from the desktop point-of-view? I want to see the front elevation at about where your breadboard says 30.

[SeneX225]

Sure thing! Here's a bunch of up-close photos:










While talking the photos I noticed that there's an actual coil value etched on the inside. It reads 1700 Ohm.

[duck_arse]

Sure thing! Here's a bunch of up-close photos:

just missed. it was the front and square of this that I wanted to see, the long front tall of the coil.

[SeneX225]

Like this? Apologies for the confusion!

[PRR]

https://www.surplussales.com/Communications/Comms-1.html

Ringing Generator  20 Hz (TEL) TA182/U  $9

[Rob Strand]

Ringing Generator  20 Hz (TEL) TA182/U  $9

Sine wave and a voltage of 90V AC comes to mind but I'm not sure if it's peak or RMS, probably RMS.

There's a good chance it will work down around half that voltage (I mean the high voltage side with the cap present.)

There's a standard for this, including operating tolerances.   The current is also standardized and there might be a series cap somewhere.  I used to have a copy of the standard but it's not so easy to get to and I may have tossed it.   You might find some info in the old Motorola Communications IC Databooks - I'm sure you will find a copy on-line.

This site shows the 2uF cap in series with the bell,
[The cap avoids DC loading the line.  DC was used to detect on/off hook.]
https://www.johnhearfield.com/Telephone/One_piece.htm

I believe the waveform on the site isn't the voltage across the bell but when the 20Hz sinewave is present or not.  Think about the sound of a phone ring it has pauses.

Whole stack of stuff here, probably too much.  The diagrams in the standards are much more basic,
https://www.telephonecollectors.info/index.php/browse/wiring-diagrams/13017-american-bell-telephone-wiring-diagrams-and-schematics-by-steve-hilsz-feb01/file

Note: the cap limits the current, so if you apply a raw voltage to the coil you might find you can use even lower voltages.

Some more details here,
https://www.sandman.com/knowledgebase/ring-voltage-tech-bulletin

Another source implied the bell current is 5mA ac to 10mA ac.

The thing missing is what is the voltage *across the bell* when the frequency is 20Hz and the current is 5mA and 10mA?

[SeneX225]

This site shows the 2uF cap in series with the bell,
[The cap avoids DC loading the line.  DC was used to detect on/off hook.]
https://www.johnhearfield.com/Telephone/One_piece.htm

First link in and I already got some doubts about validity of the project.

The bell needs a decent current to work. An exchange would apply typically 75v (rms) at 17 Hz to the line, which is quite enough to make you jump if you happen to be touching the wires when an incoming call arrives. This simple truth has surprised many young technicians and engineers. The older ones had learned long ago why their tools had insulated handles.

If I understand this correctly, the bell needs around 75 volts to work! I originally planned it to be a stompbox that will fit into a pedalboard, which implies using shared (or, at least, internal) power supply. If it would require another receptacle just to use this one stompbox, it would be very inconvenient.

What I don't understand is why does it need so much voltage? It rings (only once, true, but still) on 9v, so is there a chance it will work on that?

[Rob Strand]

First link in and I already got some doubts about validity of the project.

The main point here is in a normal phone set-up the series cap is present.

What I don't understand is why does it need so much voltage? It rings (only once, true, but still) on 9v, so is there a chance it will work on that?

I cannot remember fine details about the phone bell.  I'm not even sure of the cap limits the current or resonates with coil inductance.   

Regardless of what used to happen in the old phones with the cap, it is possible (with some effort) to choose a series cap to resonate with the coil and get the bell to operate at lower voltages.   You would tune the cap to maximize the current through the bell.

When you say it rings once, I'm assuming you mean you put DC on it and it rings, yes?

First you need to put AC through these bells so you need to build a 20Hz oscillator which can supply a reasonable amount of current drive.  Preferably something which will handle a high supply voltage for experimentation.   You don't need to make a project out of it just wack something together on the breadboard so you can get an idea what voltage across the coil is require to kick these things off.

Some diagrams show "1K ohm" for the coil.   I expect that is the DC resistance.   The inductance is unknown but would be quite high.   Supposing the coil draws 10mA (from previous unverified quotes) that means you will need more than say 10mA * 1k = 10V.   10V would appear across the 1K ohm then the additional voltage across the could would add to that (as square root of the sum of squares).

Rather than try to build a generalized 20Hz oscillator just to characterize the coil you could just try your luck with an NE555 set-up as a 20Hz oscillator.   The NE555 output is not AC, it has a DC component of Vcc/2 so you need to add a series cap on the output whatever you do.  For the non resonating cap case the output would be a large electro say 100uF.  For the resonating cap case the cap would a smaller value perhaps around 1uF to 3uF (value needs to be tuned).  Set the power rail to 10V to 15V and see how you go.


If you resonate the coil inductance with the series cap then you will get more current to the coil with a low voltage.