This bidirectional circuit was found in an American documentation from the 80's. The LEDs are common red, and the resistor is calculated according to the formulas next to the diagram.
The frequency of this Pierce oscillator, found in 1969 documentation, depends on the crystal. The...
We found this Nicad cell charging circuit in an English publication from the 1970s. The circuit can...
In the figure we have a constant current source for Shape Memory Alloy in wires or Alloy with...