This circuit is from March 1978 Radio Electronics. The 4-digit circuit uses a period module and is battery powered. The main integrated circuits are CMOS and TLL.
The sensor of this circuit, from an old documentation, is nothing more than an electret...
The presented circuit is suggested by Texas Instruments (www.ti.com) in its Application Report...
This circuit can be used in the car to convert the 12 V from the battery in 6 or 9 V up to 2 A....