The following modification may be made to the circuit to provide it with additional output current capability:



Here, six CMOS inverters (IC part number 4049) are ganged together in parallel to supply significantly more sourcing and sinking current capability than the LM339-with-pullup-resistor could on its own. Since CMOS logic gates are inherently on-or-off devices, they have no trouble handling the square wave output of the LM339.



Two questions here: first, why all the resistors at the outputs of the inverter gates? Why not just connect all the inverter outputs directly in parallel? Secondly, what value of resistor would you suggest at the output of each gate (R5 through R10)?