telephone

On 15 Jul 2006 18:52:13 -0700, in message , snipped-for-privacy@coolgroups.com scribed:

Hope you didn't miss this bit:

"The only thing your little intercom cannot do is ring the phone to tell the person at the other end to pick up. The "ring" signal is a 90-volt AC wave at 20 hertz (Hz)."

Because you obviously missed this bit:

"...a 9-volt battery (or some other simple power supply) and a 300-ohm resistor that you can get for a dollar at Radio Shack."

Yup. And if Radio Shack doesn't have a 300 ohm 1/2 watt resistor, then

Have fun Chris

I've done it.

use a 9v battery. if you get tired of paying for new batteries get a plugpack.

Bye. Jasen

it will.

ummm, try a 9 volt battery

In the pic, the 300 ohm resistor is a non-standard value - if you are using UK spec phones, go for a 470 ohm - this will extend the battery life too. Also if you are in the uk, and using modern phones with electronic ringers, you can make the bell "ring" by rigging a switch at each end to connect pin 2 & 3 of the standard line jack together. Press the button to attract the other ends attention then lift the reciever and wait for them - i.e. it won't work if you have already lifted the handset.

Yes

The article told you to use a battery. Do you mean how to get the 9V

You do not need the resistor. Modern telephones have a DC resistance of about 430 Ohms, so the two phones in series will limit the current to about

Don

Don Bowey wrote in news:C0DFABD9.3A9F0% snipped-for-privacy@comcast.net:

Obviously the 9V battery is too hard. The OP needs a simple solution like using 6 AA batteries, or 7.5 NiMH batteries. (Or 8 and a standard diode.)

Puckdropper

I wired it, and it works.

Out of curiosity, does it matter if the power is on the red wire or green wire? The wires appear equal.

Puckdr> Don Bowey wrote in

On 17 Jul 2006 20:02:23 -0700, in message , snipped-for-privacy@coolgroups.com scribed:

Terminology lesson: red is tip, green is ring. That means, on a bantam plug, red is the center conductor (the tip) and green is the outer ring of the plug. Your simple intercom is a current loop, so under normal circumstances the polarity of the voltage and the direction of current aren't important. Here's a crude drawing of how it works, ignoring the hook switch and ringer circuits:

Just out of curiosity, how are you going to let the person on the other end know he or she is being summoned to the intercom?

Alan B wrote in news: snipped-for-privacy@4ax.com:

Shouting "Hey! Pick up the phone!" would work. It at least saves you from having a shouting conversation.

This is an electronics group, though, we can do better. Isn't the ringer activated by sending a higher voltage on the line?

Puckdropper

yeah, it should be AC too... 25 to 20 Hz

Bye. Jasen

ringer

It's not critical, a 555 will do but you will have to boost the output to the appropriate voltage.

Bill has a ring generator here:

On 19 Jul 2006 09:57:48 -0700, in message , snipped-for-privacy@gmail.com scribed:

Well, it would be an interesting project to produce 90VAC 20Hz from 120VAC

Ma bell has done it for decades. The old 1A2 type phone system power supplies did it with no problems. Junk 1A2 systems can still be found cheap, or for free. They also supply the filtered DC for the talk circuit, and power for all of the lamps on the phones.

some other sort of oscilator, like a 555, you'll probably need to boost the voltage a bit though,