I need a circuit that I can take an 8 bit digital data signal and modulate it
onto a standard telephone line, and if possible a second circuit to demodulate the signal to recover the 8bit data, I would like these circuits
to be easy to construct
For 8-bits or more you'll require a complete MODEM on both ends of the telephone line. No other smaller alternative.
If you want only 10-12 numbers to be transmitted/received, you can use UM91214 DTMF generator and KT3170 DTMF decoder ICs.
Remmber, hooking up anything to your telephone line without permission of telephone company is illegal.
Without modulation data can not be transmitted over telephone line. Even if you Serial to parallel and parallel to serial converters, MOD/DE-MOD will be required.