This circuit converts a high voltage into a frequency using an optical coupler. The transistor can be 2N2646 and the coupler admits equivalent. The circuit is from a 1974 publication.
This interface or shield circuit for instrumentation was obtained in a publication from the 90's....
Mouser Electronics is supplying the SMi (Silicon Microestructures) uncompensated low pressure...
This circuit found in a European publication from the 1980s, is based on PLL 566. The frequencies...