This circuit was found in a 1980s documentation. The diodes may be general purpose diodes such as 1N34 or 1N60 and the indicator may be the lowest current range of a multimeter.
This circuit is powered by only 3 V and can flash white LEDs from 3.2 to 3.6 V, as it includes a voltage...
This circuit with the operational amplifier CA3130 was found in an English publication from 1977....
We found this circuit in the Linear Applications Handbook of the National Semiconductor of 1994....