Build A Four Transistor Metal Detector
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
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
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.
Design Your Own Crystal Oscillator
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.