This Old Phone part 3: Ring my bell.

I have the Bluetooth solution and verified operation of the candlestick handset. What was missing was an old timey ringer. Back in a day, a wall mounted ringer assemble was usually installed next to the handset.  This would require a 90V AC to ring the bell.  I want to have an old style ringer but I didn’t want to hassle with the 90 Volt requirements.   I found a surplus bell from an old phone parts supplier.  I removed the larger coil and installed a 5 volt relay with tie-wraps and wire.  I made it work.

The ringing is from a 15 to 20 Hz pulse that duty cycles on for 2 seconds and off for a couple seconds.  I piecemealed this circuit to be triggered from the incoming signal from the speaker. It sets the first 555 for the on off duty cycle while the second 555 is for the 20Hz ringing.

In order to make this a desktop application and something that doesn’t have to be anchored to a wall, I decided to create a “ringer base” which will also act as a charging station.  I found a nice small black cigar box that will serve just right for the ringer base.  The candlestick phone will sit on top and when a call comes in, lifting it off the base will cause the ringer to stop and answer the call.

I created 3 small PCBs from proto material I had hanging around my lab.  The larger one holds the ringer and charger circuit assembly.  I have a single transistor amplifier to act as a simple Schmitt trigger on a smaller PCB ( similar circuit I used for the condenser microphone from last time).  In the center is my connector board which will interface to the phone, charging power, “answer” signal, and speaker from the receiver.

The lid of the cigar box slides out. I cut out an access point to this molex connector, again from my spare parts bin, where at one point I got this assortment of connectors.  I routed out the underside so that the connector can stick up enough to mate with the base of the phone.

So far all things are in place. Next time I will put it all together with the interconnections from the phone.

This old ( Bluetooth connected) phone Part 2:

Since the old carbon microphone was not operational anymore, I needed to up grade to a more modern approach for the BC127 module. I found an inexpensive electret condenser microphone. Working with these can be a little tricky and not quite straightforward depending on the gain of target application  and how much voltage you intend to run it off. Given that I am trying to run this all off of a 3 V source, I didn’t have enough amplification to directly drive the microphone into the input of the BC127.

This this little circuit came in handy:

I built the circuit on a solder-able  breadboard and tested it with an oscilloscope first.  I verified the circuit by  testing it on the prototype platform, currently resembling a mad scientist’s tangled mess of wires.

Success! A call made from my land-line to my cell phone paired to the purpletooth jamboree board connected to this kluge of wires, iron and alligator clips was rather exciting for a geek. I was able to test the microphone’s ability to pick up my voice from about 3 feet away before dropping off.

 

Next step: In part 3, I really want to ring an old time ringer which I purchased. This will requiring hacking into the code a little bit to set a GPIO active to engage the bell. The problem is that the bell will require a higher voltage too and may defeat my dream of being somewhat rechargeable and running off of a single battery and voltage source.  At the very least, I will test the connection to the switch which will engage the “answer” mechanism ( play button on the Jamboree board).

This old (Bluetooth connected) Phone: Part 1

I inherited an old Western Electric candlestick phone from a relative, who in a previous life, converted to a nice decorative little table lamp.   I wanted to restore some of the intentional functionality of this old device  but with a modern twist. When I am at home in my office/mad scientist’s lair, I often miss calls on my cell phone because, well, I have it on silence or vibrate. I thought it would be fun to sort of “Steam-punk”  this old phone to have Bluetooth on it and have an old time RIIINNNNNG coming from an incoming call.

 

My first step was to test the Receiver ( the cone held up to the ear) with a  signal generator. I disassembled the base and removed the guts from the candlestick base. Using a signal generator, I was surprised to hear this old ear piece still worked as it did.

The next thing to test was the transmitter piece.  Unfortunately, this part had seen better days. I couldn’t pick up  a sound out of it and I feared the coil and diaphragm were frozen.  No worries, I will just use a modern microphone in its place hidden behind the mouth piece.

There was no bell in the base so that was another part I will need to get and since this style phone typically had a remote bell box, I will have to get creative on how I want to implement this.

For testing and  development purposes, the Purpletooth Jamboree development board makes for a nice break out to try microphones, speaker attachment and GPIOs. It’s based on the BC127  module from Blue Creation. The Bluetooth protocol native to this allows for a Hands Free Protocol ( HFP) as well as an audio device.

 

I was able to connect the earpiece to this development board and pair it with my phone.  I played a song from my phone and I was pleasantly surprised listening to some Little Feat being played through the ear piece.

Next step will be to get the microphone part working so I can actually have a conversation on this old phone.