Making ultra-low frequency signal generator with operational amplifier ----- LM358 LOW-FREQUENCY SIGNAL Generator

Production of ultra-low frequency signal generators with operational amplifier, LM358 Low-frequency signal generator Keywords: LM358, signal generator circuit First, the working principle The machine circuit is divided into three major modules: (see Figure 1) 1. The schematic diagram of the power supply circuit of this signal generator is shown in Figure 2. It uses 220V exchange market, with double 28V, 5V antihypertensive transformer. After the bridge rectification, the capacitive filter is filtered. Use LM7812, LM7912, LM7805 to get ± 12V and 5V DC The voltage supply signal is powered by the front of the voltage; the latter is supplied to the digital frequency display partial circuit. 2. The circuit of the waveform occurred in the waveform occurred as shown in Figure 2. Its core is an integrator composed of A1 and anchlor voltage comparator composed of A2. The operation of the circuit is described below. When stabilization, the output voltage of A2 can only be high level voltage + U02 or low level -u02. Set its initial state + U02, and U01 is 0. At this time, the voltage + U02 causes the U01 to decrease the U01 in the integrator A1. When the UTH1 = - (R3 / R4) U02 is lowered, since the voltage comparator A2 is negative, i.e., U + <0, its output is flipped to low level -u02. At this time, the integrator A1 is in the action of the input voltage -u02, and the output voltage U01 is positively integrated in constant slope. When the integrator output voltage U01 rises to the upper limit comparison level uth1, the voltage comparator A2 output voltage is high + U02, back to the working state of the negative integration. This forms an oscillator cycle. Its oscillation frequency is the reciprocal of this cycle, ie F = R4 / 4R3RC13. The integrator A1 output is a triangular wave of UTH1; the comparator A2 outputs the square wave of U02. The cycles of these two signals are the same, they are positive and negative charging slope control. Adjusting the charge, the discharge slope can change the output frequency. 3. Display circuit (omitted)

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