comparator - Lm339

Comparator to turn on LED when input voltage is > V_low_ref and < V_high_ref. V_low_ref is 3.0 V, set by R1 and R2 V_high_ref is 4.0 V, set by R4 and R5 Using LM339 which has open collector output, R3,R6, D1 and D2 are not required.