telecom call setup

Before modern electronic telephone switching systems came into use, dial tones were usually generated by electromechanical devices such as motor-generators or vibrators. In the United States, the standard "city" dial tone was a 600 Hz tone that was amplitude-modulated at 120 Hz.

Off-hook tone

Bell System Voices
Time Lady
Mary Moore
Jane Barbe
John Doyle

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dial tone sound effects

There isn’t a standard off‑the‑shelf transformer designed to step up exactly 5 V AC to 90 V AC. To achieve that ratio (about 1:18), you’ll either need a custom‑wound transformer or use a more practical input voltage (like 12 V or 24 V AC) with a small step‑up transformer. For low‑voltage sources such as 5 V, a DC‑DC boost converter is usually a better solution than a pure transformer.

Call Set Up 2:

Bell System
Step By Step
Line Finder

Step By Step Relay A,B,C,T

Arduino

Raspberry Pi Pico (RP2040)

KEY
DE-BOUNCER

IC's

TTL
LS18 DeBouncer

7490 BCD decade counter

7442 BCD to Decimal Decoder
YouTube

(7447, 7seg display + com)

(7449, 7seg display - com)

DTMF
MT 8870 DECODER

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Arduino Debouncer
LS18 Dbnc Chp LS18 Datasheet + 0.1uF Film Capacitor
DigiKey LS18
Ebay 7442 14 pin BCD to DECIMAL Chip

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SCHEMATIC YouTube Source

Google: Bell System step by step line and cut off relays schematic

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YOUTUBE RING
YOUTUBE SYSTEM
PDF 9 :-)
PDF KTU 1
PDF KTU 2
207C KTU $
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YouTube Telecom
YouTube Prfile
URL Links
Patrion
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