Free Circuit Diagram

This circuit is another radio frequency (rf) field strength meter, similar with our previous field strength meter circuit, but with lower supply voltage (only a single cell 1.5V battery). Here is the schematic diagram of this rf strength meter circuit: To use, turn on transmitter and meter; adjust C1 for peak [...]

The excellent high input impedance, high slew rate, and high voltage qualities of CA3140 op-amp make it suitable for Wien-bridge sine wave oscillator. The basic circuit for Wien-bridge sine wave oscillator is shown in the figure below (the upper part). You can see the formula in the figure, when R1=R2=R, and C1=C2=C, then the formula [...]

Notch filter is known as band-cut filter or band-reject filter. The fuction of this filter is to remove some frequency portion of a signal. The schematic diagram of this filter circuit, a second order notch filter is depicted in the figure below. The formula is actually complicated, but by taking the R3=R4 and [...]

Using a single supply quad comparator LM339, LM239, LM2901, LM2901V, NCV2901, or MC3302, we can build a square-wave oscillator with simple circuit and formula. Here is the schematic diagram: This circuit is suitable if you need  many square-wave oscillators in one circuit, since the quad packaged comparator provide four comparators in one single  [...]

Using only a single transistor and few passive components, you can build a fairly sensitive peak detector. circuit This peak detector circuit is suitable for audio application, since the average sum of positive and negative cycle of audio signal has equal value. You can find a peak signal although you only detect the peak of [...]

Metal Detector Circuit Topology One of the simplest method of metal detecting is by beat frequency oscillator. Basically, the circuit consist of two balanced oscillator. One oscillator provides the reference signal, and other oscillator is acting as the detector element. The reference oscillator’s frequency is fix, while the detector oscillator is variable depending on [...]