How to ground the arduino?

Hi guys,

I have tapped the audio signal coming from my telephone. It´s about 0.05 volts if someone talks. Now I want to measure it with my arduino analog in pin if voltage is applied (if someone talks) and swicht a digital output high. (to light a LED to let my college know that I´m talking at the moment) So my question is: Can I connect the groud of the audiosignal to the ground of arduino and the audio "hot" to the analog in pin WITHOUT damaging either the phone or the mc. I´m doubtful that is that simple I think, so i want to ask.

Important is that I don´t want to power the arduino with batteries, i need it powered with usb from my pc.

Can someone give me advice to solve that or push me into the right direction?

Thanks for any help! amp

There are several telephone types in the world, so your phone may be different from those in my home country. Here are some ideas :

1 When a telephone rings, 40 volts will ring a bell on old land lines in the old country.

2 If the signal is only 0.05 volts in your country, it is safe to place a diode between the two wires to clamp the voltage to less than 0.70 volts without interfering with the voice. That diode can protect the Arduino from large voltages that you failed to measure. Put two diodes on the wires, back to back to suppress negative and positive voltages over 1.00 volt.

3 Test the ground wire with an ohm meter to see 1 ohm from telephone ground to any known ground. Maybe it is not ground, it might be a hot two wire system with differential signals in your nation. If it is not a ground wire with .1 ohm to a reference ground, then it might be unwise to believe it is a ground wire.

You need an isolation transformer between you and the phone line. Then treat one of the oputput windings as ground and the other as audio. Because of the high signalling voltage you need to protect the input of the arduino from this, here are some ways you can do it. http://www.thebox.myzen.co.uk/Tutorial/Protection.html http://www.digikey.com/us/en/techzone/microcontroller/resources/articles/protecting-inputs-in-digital-electronics.html

Most countries do not allow connection of equipment to the public telephone system that is not "type approved" so this will probably be illegal.

I guess its illegal to connect this http://www.rapidonline.com/audio-visual/velleman-telephone-amplifier-kit-70-4130 to the phone network then.

Legal to sell, illegal to use?

sirampersand: Can someone give me advice to solve that or push me into the right direction?

You need isolation. Connecting external devices to telephone wires is a big no-no.

An opto-isolator should do the trick (google it).

Lakes: I guess its illegal to connect this http://www.rapidonline.com/audio-visual/velleman-telephone-amplifier-kit-70-4130 to the phone network then.

Legal to sell, illegal to use?

I don't know if it's legal or not but on that page it says: "Input Isolation transformer interface"

Key word: Isolation - there's no direct path from the telephone line to anything else.

Lakes: I guess its illegal to connect this http://www.rapidonline.com/audio-visual/velleman-telephone-amplifier-kit-70-4130 to the phone network then.

Legal to sell, illegal to use?

Only to install, it is perfectly legal to sell.

Many years ago I produced an acoustic coupled modem, with only a speaker and microphone acoustically coupling it to a telephone handset. This was actually illegal to use but I could sell it. I took the precaution to put a warning triangle on the PCB which said "illegal to connect to a public telephone system" that stopped me being prosecuted. But BT were all over the Magazine it was published in because they took out my comments in the text that using this was illegal. The editor just did not believe me. And that was with no electrical connection, just sound.

first, let me fill in what OP asked “to light a LED to let my college know that I´m talking at the moment”

next,

sonnyyu:
however we are in Arduino forum and fall in this situation - “if all you have is a hammer, everything looks like a nail”
“if all you have is a brand name Atmel hammer, everything looks like a brand name Atmel nail”.

Here we go- The pots line and MCU/Arduino interface;-

next, The item OP is truefully need;-

This circuit is a simple circuit which prevents picking up other telephone when one telephone is in use. This can be done easily by installing this type of circuit between any telephone and the telephone line.

This type of function is very useful when you don’t want other people from disturbing your modem connection or listening to your telephone calls by picking up other telephone connected to same line. The idea of the circuit is to sense the voltage in the telephone line when the telephone is picked up. If that voltage is higher than about 30V (normal on-hook voltages is about 48V) then the circuit lets the telephone to work normally. If the voltage is lower 30V it prevents the current from going to telephone line to telehone (normally the voltage in line is about 6-10V when one telephone is off-hook). The circuit is designed so that is passes the ring voltage to all telephones without problems.

http://www.epanorama.net/circuits/tele_privacy.html

last, if u still need tap the phone for other purpose.

just like Lakes told, make sure it is legal at your country.

final caution: the pots line might be last life savers. don’t do anything unless you know what you are doing.

Hi Folks,

First of all : thanks for your many answers! But it think this goes in the wrong direction because I didn´t tell you more about the phone. About legality: dont worry, it´s no public phone! It´s a company internal digital, ip phone, powerd by an poe switch, and the audio out is - im 100% sure, a preamped, digital to analog converted signal. It is like the "headphone out" from your cd player. I works perfect with my standard 3.5 headphones (about 35 ohms) as well as with the line in of my hifi amplifier.

amp

sirampersand: Hi Folks,

First of all : thanks for your many answers! But it think this goes in the wrong direction because I didn´t tell you more about the phone. About legality: dont worry, it´s no public phone! It´s a company internal digital, ip phone, powerd by an poe switch, and the audio out is - im 100% sure, a preamped, digital to analog converted signal. It is like the "headphone out" from your cd player. I works perfect with my standard 3.5 headphones (about 35 ohms) as well as with the line in of my hifi amplifier.

amp

great, then what is make of your VOIP server and ip phone model? This time you better tell us complete story. What you ask at most case could be easily done by add/modify profile of VOIP server to turn on programmable led at ip phone while you are talking (yours, your college's or whole company's, if you are important popular enough. :P). You might need post same question at your VOIP server forum.

You have is a brand name Intel hammer, but you ask brand name Atmel nail.

sonnyyu: if you are important enough.)

I´m not. =( popular? yep! :-) even I where, i want to drive a digital pin high - for the love of arduino ;) The background is im working in 1st level support and we are talking a lot on the phone, even if we´re not talking, we are listening and watching other computers. often we need to ask each other, never knowing if the other has a phone/vnc connection running or not and if i am disturbing or not. same with colleges comming in the door and starting to ask or telling their problems while me the agent talks to someone else - annoying ! so if i have a digital pin shifted high on that trigger i coud switch anything, a well positioned blinking led, a red lighted sign " agent calling" or what ever, dont know yet! the voip phone/server would be the wrong media ... cheers amp

I know I made a mistake to use word "important" and it should be "popular", nobody want to talk important person at corp level at least very offen.

first, your people could use Do Not Disturb or DND functionality of VOIP, might be used already.

next, use IP phone expansion module to monitor each other DND and online status.

The expansion module is designed for receptionists, administrative assistants, call center agents, power users, and executives who need to monitor and manage a large volume of calls on a regular basis.

The one at picture is 36 keys with LEDs model, could have less or more one.

I have hard time to understand what Arduino to do here, might be because I drink too much Italian Arduino coffee this morning. ;)