LED Bar-Graph Level Gauge

The MAX931 series has capability to produce high output source which is useful for driving LEDs. The circuit below shows an example of simple four-stage level detector. Vin=(R1R2)/R1 volts gives the full-scale threshold (all LEDs on). The other thresholds are at 1/4 full scale, 1/2 full scale, and 3/4 full scale. The current into the LEDs is limited by the output resistors. Here’s the circuit diagram:

[Source: MAXIM Application Note]