I am looking for someone who can build a custom circuit for hire. I''d like to run it off a 12 volt battery, be connected to a POTS phone that's not connected to anything else, and generate a dial tone for lets say five seconds after the handset is picked up.
I just picked up my landline phone to listen to what a dial tone is, and it seems like all I heard was an F and A below middle C together. Sounds like something that could probably be rustled up with the electronics project kit I had as a kid. (I don't remember who made that kit. It was in a box made of actual wood. I don't remember if the components were mounted on plastic or cardboard. The terminals for attaching wires were little springs; you'd just bend 'em and stick the ends of wires between the coils.)
Looking online, I find the North American dial tone is dual frequency, 350 Hz + 440 Hz. Different geographies have different dial tones. "The modern dial tone varies between countries. The Precise Tone Plan for the North American Numbering Plan of the US, Canada, and various Caribbean nations specifies a combination of two tones (350 Hz and 440 Hz) which, when mixed, creates a beat frequency of 90 Hz. ..." Dial tone - Wikipedia
