Based on TTL logic this circuit can vary both the frequency and the pulse width of a rectangular signal. Equivalent components can be tested.
We found this circuit in an Australian publication from 1991. The circuit has good sensitivity, presenting...
This circuit from the 80's makes use of two transconductance operationals of the time. Modern...
We found this circuit in the March 1980 Radio Electronics magazine. The circuit used is the HA2400...