We found this circuit in the August 1990 issue of Radio Electronics magazine. The two-digit circuit uses a pressure sensor and is powered by a 9V battery.
This two stages amplifier is used with high impedance earphones. The transistors are very old...
August 2017 - The new N-channel MOSFETs from Vishay's TrenchFET Gen IV family can now be purchased from...
This circuit is from a documentation on the MC1539 from Motorola and may, however, be implemented...