Please be sure to place all the LEDs with the right polarity. HereвЂ™s what the assembled PCB looks like. This ramp cycle repeats continuously and VR1 can be adjusted to change the ramp speed. The output ramp voltage enters the falling phase, which causes the LEDs to fade away. At this point, the output of U1G1 will start decreasing and the capacitor will start to discharge and charge with the opposite polarity. This output is connected to the left terminal of C1 and eventually, it will be at a higher potential compared to the right terminal. The output of U1G2 will increase as the voltage difference between its input terminals increases. Logic Gates Logic gates are electronic circuits that process signals that represent true or false values. But when I interchange the LDR with photodiode, phototransistor and transistor (L14F1) my circuit works well without changing any other components. The schematic symbols for op-amps usually donвЂ™t show the pins that arenвЂ™t used in the circuit, as is the case for the LM358 symbol above where only five of the eight pins are shown. I have made the circuit with LDR and few more components. For this I will use LM358 IC which is operational amplifier. The ramp output voltage is also fed back to the positive terminal of U1G2, while the negative terminal of U1G2 is held at the same reference voltage from the R1-R2 voltage divider network. In this project a protoype circuit which can switch on the device when the light falls on it. The ramp waveform is in its rising phase which causes the LEDs to start glowing brighter. When first switched ON, the output of U1G1 is HIGH and this causes the capacitor to start charging with the polarity as shown. The negative terminal is connected to the capacitor C1. The values of R1 and R2 keep the positive terminal at a fixed voltage that is half of the supply voltage. The positive terminal of U1G1 is connected to a voltage divider network consisting of R1 and R2. Are you wanting rail to rail operation A +/-5V supply for the opamp. The op-amp section is designed to give us a ramp-like output that is fed to the base of the transistor which in turn controls the LEDs. Absolutely not, the LM358 is completely unsuitable for audio, its extremely slow. Internally, the LM358 contains two op-amps which are both being used in this circuit. Transistor Q1 is used to control the LEDs and it will switch from the cut-off to linear, to saturation region depending on the voltage applied at its base terminal. WeвЂ™ve used the LM358 op-amp in the previous project and to quickly recap: itвЂ™s an analog device whose output is the difference between the voltages at its two input terminals. Use R5 to adjust the gain of op-amp LM358. This mic pre-amplifier circuit operated with 9V DC voltage, you may use 9V battery for this circuit. The circuit is very simple, inexpensive and easy to built. The heartbeat or breathing circuit is a nice little LED project that makes use of a relatively simple circuit. Here the simple mic pre-amp circuit design based on single IC LM358.

Lm358 schematic