I need help designing a circuit, it will be a tachometer calibrator. It will input 5V square wave signals from a Fluke 741B, nothing higher than 3kHz & it can't draw much current from the input. It will have a high intensity LED and a battery pack, something along the lines of 4 D Cells. The LED I have has a VF of 3.1V with a current draw of .2A (no P/N on this guy, just found it in my drawer). Is something as simple as a Darlington pair & voltage regulator sufficient for this, say a 2N3904 feeding a TIP31? Is a common emitter or common collector configuration better suited for this application? I have a very hard time designing circuits, I'm just looking for a little guidance.
Thanks for the time, Steve