This digital to analog converter circuit was found in the March 1980 Radio Electronics magazine. The power supply should be symmetrical, and the digital controls can be TTL.
We found this circuit in a technical documentation on the National Semiconductor LM3909. The...
The LEDs act as diodes, so if good they will show the same characteristic curve. Arrangment shown...
This circuit is from an old English publication from 1968. We can implement it with TIP32...