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Battery and Resistor Alternatives

Posted: Sun May 01, 2016 4:45 pm
by softbaugh
A simple phone circuit can be made with a battery and a resistor. This approach is a favorite of science fair projects, but we wanted a more robust design. One problem with the battery and resistor option is picking the right resistor for the phones used (from the point of view of the resistor circuit, different phone models behave differently).

The field phone host board, on the other hand, provides a constant current (about 30 mA per line, or about 60 mA when bridged), which works across various phone models without any guesswork. This approach is very similar to what the actual telephone company provides.

Even so, the battery and resistor circuit is a cheap and useful circuit to know for some limited applications. Have a favorite circuit? Tell everyone about it and your experiences with it here!

Re: Battery and Resistor Alternatives

Posted: Thu May 05, 2016 7:24 pm
by softbaugh
Options suggested by Gatorbait3014:

Ramsey Electronics manufacturers the Model # QLRD1
Viking Electronics manufactures several models. The DLE-200B supports two telephones. Viking Electronics also offers a free PDF document on the subject:
https://www.vikingelectronics.com/products/appnotes/ringdown-guide%28832%29.pdf
Teltone offers their TLS-4 Telephone Line Simulator, which supports four(4) lines.