Making Old Telephones Great Again (MOTGA)
I finally silenced all of the telemarketers, but that ain't what this here post is about.

Yesterday, I mentioned that I would be building a call progress tone generator today. As the name suggests, it's an electronic thingamabob that generates the dial tone, busy signal, ringing tone, and other audible signals to keep the caller informed about the progress of a call attempt. And here here it is:

I had originally intended to build the whole module on a single board, but as I got to laying out the components, I became concerned that there wouldn't be enough room for all of the bias resistors, so I stuck part of it on a little headboard instead. That ended up saving my bacon because I made a mistake when building the headboard, and had to do it all over. If I'd done it as a single board, I would've had to redo the whole module.

So here's how this thing will (hopefully) work. The thing at bottom right is a microcontroller board that operates the module in response to commands sent over a USB connection from the main computer. The socket at bottom right is for the tone generator chip itself. The blue box above it is a relay. When the module is powered up, the tone chip's enable pin is connected through the relay to a power-on-reset circuit. After a few seconds, the microcontroller tells the relay to connect the enable pin to an output pin on the microcontroller. The socket on the headboard is for a channel selector chip. The microcontroller instructs that chip to route the tones from the tone generator to one of eight telephone lines.
Holy shit...

You must be like a genius or something.

Have you...

By chance thought about donating to our sperm bank?

I've been truly blessed by the sheer volume of geniuses (and really really good looking people) on this website, wow.

Group Hug
My old sperm won't keep that long. You need to get it fresh from the tap. Call now for your free insemination session while supplies last!
If I had a dime for every time I've heard that one!
Hey, you asked for it. I didn't volunteer. LOL
So I finally got the tone generator working, and come to find out it doesn't use the same frequencies as Ma Bell. It sounds like some fucking VoIP office system tones, which shouldn't have come as a surprise since that's what the chip was made for. It's disappointing just the same. This is the realness right here:

(Scroll down for the progress tones.)
941Hz is real purdy.
The thing I hate most about this chip is that the 440Hz and 480Hz they use for the ringing tone don't beat together the way 400Hz and 450Hz do in the real phone system. Reminding the caller of a ringing bell is kind of the whole point of the tone.
I got up dark and early this morning and built a switch. It's the circuit on the right.

The big chip up top is a switch array. It contains 64 electronically controlled switches in an 8x8 matrix. This will be used to connect the audio inputs and outputs of the telephone interfaces to establish calls. It'll handle 4 simultaneous calls.

The microcontroller at bottom right and the voltage regulator circuit at bottom left are the same as for the call progress tone generator (left).

Although it looks like a mess of wires, this circuit is simpler than the tone generator. There were a metric shit ton of bias resistors to solder, but it proved to be less of a pain than I thought it would be. I made a few gaffes and blunders while building it, all easily recovered.



This inspires me to work on a project I've been thinking about.
I can't help noticing you, hot stuff. Back dat ass up!

What kind of project do you have in mind? I'll donate my body to the cause if needed.
You're making me touch myself now.

That broad is nice and meaty. Wanna help me do her?

*shrill and frightening screaming*
I love those meaty broads...

You know me so well!!!

I prefer the meaty dudes though...


So thick and meaty and delicious.

Are you meaty RB?
Nah, I'm a skinny old bird. Meaty where it counts though.

*bats eyes*
Are you trying to seduce me, young lady? Well, whether you are or not, it's working.
I love it when people geek out about things. Take this fellow Jeff, for instance. He's a real geek's geek.

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