1W White LED Night Light - As many of you know, I have a pet peeve with poorly made LED night lights. Often, the light from the LED quickly fades, so within months, the light is useless. I have posted several versions of modified night lights using higher quality components. This circuit is yet another version, which produces much more light than those other designs. . . . Hobby Circuit designed by David A. Johnson P.E.-November, 2008
2-wire Game Show Time - Several Game Show timers included, scroll to find this one. The game show timer determines which contestant presses their button first by lighting a lamp and ringing a bell and the slower contestants are locked out. The circuit is convenient in that only two wires are needed to interconnect the stations and the wires may all go back to the base unit or they may be "daisy-chained" between stations. There is no electronic limit on the number of stations. The circuit uses a 24 volt power source and 12 volt lamps when built as shown but the experienced experimenter may scale these voltages along with the zener voltages if desired. If the SCR triggers when the power is applied or when the reset button is pressed, add a 0.1uF capacitor from anode to cathode. (A sudden increase in voltage across some SCRs can trigger them, especially if the gate impedance is high.) __ Contact: Charles Wenzel of Wenzel Associates, Inc.
3-up Decision maker - This electronic device will help you make important decisions (or not) . While it is deciding the solution to your problem it will convince you how difficult it really is by a painful growling noiseor maybe this is normal when you have to think!__ CdS Electronic
4-20ma Current Loop Tester - This circuit injects an adjustable current through a wire loop. Using a digital current meter, the current can be adjusted from near zero to over 24 milliamps. . . Circuit by David A. Johnson P.E.-May, 2012
5-Finger LED Counter - Our FIVERP5 has many applications; Teach your children how to count to five! Draw attention and a smile. Press the push button five times and trigger your hobby rocket, etc. The unique small design will allow you to mount it almost anywhere. Operate it with 9V battery, 12V car battery, four 1.5V batteries, or via one of our battery simulator kits. The alternative uses are endless. __ Contact: Kit from Elich Industrial Development, Corp
60 Watt Lamp with Auxiliary 14v LED Lamp - This circuit controls power to a standard 60 watt lamp plus generates an auxiliary 14v DC supply which can power an automotive style 12 LED array. . . Circuit by David A. Johnson P.E.-July, 2006
6v NMH/NiCd Battery Tester - I designed this circuit to test rechargeable six volt battery packs under constant current conditions. As designed, the circuit applies a 10 amp load to the battery pack. A heat sink must be used on the main power transistor. . . Circuit by David Johnson P.E.-December, 2004