This circuit is from the 1992 Radio Electronics Handbook. The components used are from the period, with emphasis on the 2-digit display driver.
Based on a 555, this 80's American documentation circuit detects the voltage of a battery and can then...
In the figure we have the use of one of the four existing amplifiers in the LM2900 and LM3900 as a...
12 V battery chargers provide higher unregulated voltage. With the regulator shown, obtained from...