JFET High Impedance Buffers  -  I have used these circuits many times.  They are great when you need a low gain AC signal amplifier with a very high input impedance.  It is good to beyond 50MHz . . . [Circuit by Dave Johnson P.E.,  07/11/06]

LED Flashing Badge #1  -  I have seen numerous flashing light badges at trade shows and conventions. They are often handed out as gifts to promote some business. The devices often use inefficient circuits, which cause the battery power source to be quickly depleted . . . [Circuit by David A. Johnson P.E.,  03/26/02]

LED Flashing Badge #2  -  This circuit uses a CD4013 dual D Flip/Flop IC.  A single lithium battery will provide months of continuous LED flashing.  It also has a tiny push-button switch to turn on and off the light flashing . . . [Circuit by Dave Johnson P.E.,  03/26/02]

N-Ch & P-Ch Transistor Form Push-Pull Driver  -  This circuit can produce high speed output signals with fast rise and full times. The unique change pump action allows the voltage of the upper P-ch device to range from millivolts to hundreds of volts. The output current is only limited by the rating of . . . [Circuit by David A. Johnson P.E.,  06/27/00]

Peak to Peak 300v Signal Generator  -  This circuit converts a square wave signal to a +-150 volt output signal with fast 100nS rise and fall times . . . [Hobby Circuit designed by Dave Johnson P.E.,  06/03/00]