Use old phone as microphone

Perhaps this

microphone

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Thanks! I will try that! :-)

This should solve the input part (the microphone). But how connect the line out to the phone speaker?

Thank you!

Or.

These microphones usually behave as a variable resistor, So you need a voltage source, and a dropper resistor to act as a potential divider, and give you a voltage output as the resistance varies. The microphone can be used as either resistor in the divider. Using it as the bottom resistor, allows the casing to be connected to ground. Either connection results in a significant DC voltage being present on the output. This is 'OK' if the line input is AC coupled, but otherwise a capacitor must be included in the circuit as shown.

Best Wishes

Bingo !

I wonder if he actually has an old carbon granule capsule ? !

Film ppl use them to errr... 'simulate' the sound of an old telephone. ;-)

I guess you could do it in DSP but ........

Graham

Those old carbon granule capsules had terrible distortion. Back in my acoustic muff modem days I found I was better off handling the outbound signal with magnetic coupling to the earpiece.

...Jim Thompson

I was designing 300 baud muff modems for GenRad portable testers from

...Jim Thompson

Even the best of the new ones only really capture a select subset of the original B3/Leslie combo. What a fantastic contraption.

Bob

Use Roger's suggestion instead. It's better (see below). The capacitor can ne 0.1 microFarad or more. A 1.5 volt battery would probably be ok. Just connect the audeo out directly to the earpiece for starters. If the volume is too low, you may need to match the impedance with a transformer or amplify the signal.

These microphones usually behave as a variable resistor, So you need a voltage source, and a dropper resistor to act as a potential divider, and give you a voltage output as the resistance varies. The microphone can be used as either resistor in the divider. Using it as the bottom resistor, allows the casing to be connected to ground. Either connection results in a significant DC voltage being present on the output. This is 'OK' if the line input is AC coupled, but otherwise a capacitor must be included in the circuit as shown.

snip

"shake" as in "whack sharply on something wood".

Anything new will have a cermet condenser mic.

Hello Graham,

Probably. In that case it may be necessary to give the capsule a good shaking, especially if the thing sat in the attic since the 80's.

Ah, nothing like the sound of an old phone. We have a Western Electric wall phone with crank. When that there thang rings the birds fall out of the trees.

Best of all, when you answer it the people on the other side really think that Edison is speaking to them.

Ain't the same. I guess they figured out how to mimic the sound of a Hammond organ by now, pretty close at least. It took about 20 years...

Still, I slaved days and days over one of these to revive it. And boy does that sound great.

Regards, Joerg

Actually, tapping it against something like a table might do better, especially if you rotate the element and give it a tap from several different sides.

I remember talking on the old carbon-mike phones, and when the sound got scratchy, you'd take the "receiver" (handpiece), and hold it by the ear end, and whap the mouth end against the heel of your hand. If that didn't work, you'd whack it on the table. That usually cleared up the scratchiness.

This is probably the origin of the "If it don't work, whap it" philosophy. ;-) [I swear, one of the pieces of test equipment I used at my video game repair job was a "RAM Tester", and there was a note on a piece of masking tape: "If not working, wap it." I swear I am not making that up. And it _did_ work!]

Intermittent connections are the worst things there are, except maybe politicians and lawyers. ;-)

Thanks, Rich

Hello Jim,

No wonder, considering the way they work. All you do when yelling into the carbon mass is shaking the granules a bit, hoping the electrical resistance change is intelligible. In modern ENOB numbers these mikes would probably clock between three and four.

I soon gave up on the magnetic coupling. Hotels started having modem jacks on their phones and the public phones, at least in some European countries, went to a more vandal proof design. That meant they made the receivers out of metal.

Regards, Joerg

Hello Bob,

The XK-3 will set you back a good $2000. Also, it doesn't spread that Hammond oil smell after running for a few hours.

Regards, Joerg

Hello!!

I tried as you show below (with the capacitor). It works fine, but the volume is very, very low.. I almost can't hear.. You said that, in this case, I must match the impedance with a transformer, or amplify the signal. How? A simple BC548 can amplify enough? I tried to buy that 600R transformer, which is usually found in modem cards and on some circuits on sites (like

Aga> > Thanks! I will try that! :-)

probably be ok.

volume is

signal.

Hello Tim,

"New" meaning one of those phones where the plastic of the receiver is so flimsy that a firm grip creates squeaking noises? I bought two office phones from a large and reputable company. So they weren't exactly cheap. The squeaking of the plastic became so annoying that I retired both and replaced them with older Panasonic phones from a yard sale. Much better, no squeaks, more tolerant against low line current (a problem out here).

Regards, Joerg

Hello Richard,

Carbon particle mikes also require that the phone sees a certain line current, usually around 25mA.

Regards, Joerg

Thanks

I didn't know that.

Really need to establish what sort of mike the OP has in his handset.

The idea could be used for Skype - if there were a way of telling the package that the phone had been answered when the phone was taken off the hook.

Hello Richard,

Since he said "old" it might just be that old carbon mike. The way to tell is to unscrew the lower cap, after which the carbon mike should almost fall out and then gently shake the mike. A light hash usually indicates carbon particles. If the receiver doesn't have caps that can be opened it most likely isn't really on old phone.

I don't know much about Skype. Probably wouldn't work for us anyway since there is a HW firewall. Some day there may be a gizmo that "translates" between a regular phone and the PC. IOW, signals an off-hook condition, sends the tone dial info across and so on. Maybe there is something already, else it'll be just a matter of market size until some company offers a USB translator box.

Regards, Joerg