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My dad is having difficulty hearing his cordless phone ring in his shop, due to ambient noise. He has the phone connected to a Straight Talk home phone service device. So, there is no legacy analog line. I am trying to drive an external ringer that was built for an analog system. The Straight Talk jacks do not output sufficient current to drive the ringer.

Is there a way I could use a ring detector and relay? Does anything exist? How difficult would building something be? I have read that the old ringers require 90 VAC. Is that correct?

Sorry. Lots of questions in one post.

Thanks in advance for any info, ideas, suggestions, etc.

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  • \$\begingroup\$ You can use a transistor or MOSFET to take the signal from the jack and drive the ringer. Google something like: "Drive DC motor with MOSFET" and replace the DC motor with the ringer in the actual application. \$\endgroup\$
    – Nick Williams
    Aug 26, 2015 at 23:10

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For quite a while, Sparkfun had a series of wireless desk phones with the circuit housed in an old Bell System 500-style case. So you could have an old-style black desk phone with a rotary dial and old-fashioned ringer, powered by a Li-Poly battery and connected to the telephone network by a cellular modem.

Since there was no phone line to activate the ringer, they built their own high-voltage circuit. These phones have been retired from the Sparkfun catalog, but per their policy the information is still available including schematics and datasheet.

Here is a link to the schematic. The high-voltage ringing circuit is on page 3, which I have copied below:

enter image description here

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    \$\begingroup\$ Beware the Sparkfun schematics. Lot of errors. For example the above NJM2670 requires a 5 volt VCC supply, but Sparkfun is supplying only 3.8v via the mosfet switch. \$\endgroup\$
    – Jack Evans
    Aug 30, 2017 at 4:19

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