This circuit for low frequency data transmission was found in the May 1977 issue of Radio Electronics magazine. The circuit modulates the signal at two frequencies for bits 0 and 1.
This filter, from an audio publication from 1977, passes the frequency range corresponding to the...
In the figure we have three voltage doubler configurations that can be used in high and low...
This circuit was found in Motorola documentation from 1966. The lamps are according to power and...