Build A Four Transistor Metal Detector
February 2008
Want to be a treasure hunter? By discerning subtle changes in frequency, this design is capable of detecting coins to a depth of three to four inches. The circuit can sense a soda can at a depth of six inches and metal pipes at an even greater distance. The unit is powered by two 9V batteries in series. The detector has a current draw of approximately 9 mA at 18 VDC. As a result, the batteries should last a long time...
A SIMPLE ONE-MHz FRQUENCY COUNTER
March 2004
If you work with digital or analog oscillators, at some point you will want to double-check their operating frequency. Analog oscilloscopes will only get you within a half-order of magnitude or so; a good frequency counter will take you the rest of the way.
AN ANALOG SINE WAVE SIGNAL GENERATOR
June 2004
A sine wave signal generator can be used to measure the frequency response of filters and amplifiers. Simply connect the signal generator to the input of the circuit under test and adjust the output of the generator to an appropriate amplitude. Next, measure the output voltage of the circuit at various frequencies with an oscilloscope. A frequency response graph can then be plotted with this data.
AM Radio Tx
November 2004
Use Your Boombox as a PA System
Design Your Own Crystal Oscillator
August 2006
If you would like a circuit that is useful in obtaining a high-accuracy, low distortion RF source capable of driving a 50 ohm load, then you’ve come to the right place. The circuit in Figure 1 is the schematic for a common collector series tuned Colpitts crystal oscillator.
Build A Flood Detection Alarm
May 2007
Is there water in your basement? Or anywhere else it shouldn't be? This simple water detection alarm will alert you when it starts to happen.
Build A Model Railroad Crossing Signal
December 2007
Creating authentic looking models is a passion of mine. To enhance my model railroad setup, a realistic (but inexpensive!) crossing signal was just the ticket.
