Circuit makes simple FSK modulator: 10/11/2001 EDN - Design
Ideas / The need for a compact telemetry system poses a
challenge for designing a small, light, low-component-count
system. Interfacing serial data from the microprocessor is also
difficult because most low-cost RF transmitters do not accept dc
levels at the input. Commercial FSK (frequency-shift-keying)
modulators are bulky and need many passive components. .