This circuit was published in an article in Radio Electronics magazine in October 1988. It uses components that are still common today, except for the sensor, which is a special type from that time.
The AT21CS11 memory device offers an extended voltage range to accommodate lithium-ion battery...
The LMV321 is a low voltage operational amplifier from ON Semiconductor. The following diagram,...
This circuit is from an old 1967 publication. The circuit uses a programmable unijunction...