DTMFOUT vs CM8880 tones
FlyingFishFinger
Posts: 461
Hello!
I have a working phone line interface and am able to dial with both the CM8880 and with the DTMFOUT command. However, when I listen in with a phone on the same line, the tones from the Stamp are WAY louder than those from the CM8880. What accounts for this difference? I have tried running the quiet tones through a 386 amp, but what I got out was only noise, no more tones. How can I adjust/ increase the output volume?
Thanks
Rafael
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You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~
I have a working phone line interface and am able to dial with both the CM8880 and with the DTMFOUT command. However, when I listen in with a phone on the same line, the tones from the Stamp are WAY louder than those from the CM8880. What accounts for this difference? I have tried running the quiet tones through a 386 amp, but what I got out was only noise, no more tones. How can I adjust/ increase the output volume?
Thanks
Rafael
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~
Comments
Rafael
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You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~
An LM386 is intended for 4-32 ohms.· The phone line is/wants about 600 ohms.··RadioShack has an audio transformer, 1kohms:8ohms.· The high-impedance side is tapped so you could use it as a 500:8ohms transformer and that way the impedances would be closer.
It's bad form to couple into the phone line (i.e. Public Switched Telephone Network) without using a FCC Part-68 registered protective coupler [noparse][[/noparse]interface.]· If something goes awry without that -- then your tail is a sail and the phone company is a hurricane.
I use the circuit from the Nuts and Volts article number 19. I realized that the tones going through both ways are reduced by the interface. I have a headphone connected it, and the DTMF from the line is on the soft end of comfortable and the DTMF from the Stamp makes my head hurt. However, when I listen to it on the other side, it sounds normal.
This is not intended to be commercialized or mass-produced, besides I wanted the learning experience of making something like this...
Thanks
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~