MaBell Project Plan v3: Line Voltage and a Real Bell #
Plan: MaBell Bluetooth Gateway: Project Plan Β· Previous: v2: A low-voltage phone Β· Next: v4: Boxed and installed
A vintage rotary phone rings and works at line voltage, and the circuit board’s line interface is chosen. Status: planned. Its definition of done and tasks are written when it becomes current.
π Build guide:
notebook/build-guides/slic-module-build-guide.md
Scope #
A SLIC (subscriber line interface circuit) gives the phone a real ~48V battery feed, 600Ξ© line and ringing voltage. The AG1171/KS0835F module does this from one 3.3β5V supply; the phone side goes on screw terminals or a protoboard, since tip and ring carry ringing voltage.
- Call tones: through the SLIC’s hybrid into a vintage phone’s earpiece.
- Ringing: a real mechanical bell. The firmware toggles the module’s F/R pin at 20 Hz to ring, and handles ring-trip when the phone is answered mid-ring.
- Hook detection: the module’s SHK signal, which is active-high, so the firmware inverts it.
- Rotary detection: pulses read from SHK.
- DTMF detection: from the SLIC’s receive audio.
- Call audio: through the real 2-wire to 4-wire hybrid.
- Optional: a discrete HC-5504B SLIC with the LT1684 ring generator, on perfboard. It needs β48V and +12V supplies, a 90V AC ring generator, line protection and a hybrid network.
- The decision: which line interface goes on the circuit board, AG1171 module or HC-5504B, recorded with the options considered in the project’s design docs.
Not in v3: the circuit board and enclosure (v4).