# Question about resistors and capacitors in a circuit

• XuFyaN
In summary: The purpose of R4, R5, and C4,C7, and C8 is not fully understood, but they are probably necessary for some function related to the circuitry. R4 is probably the collector resistance for a common emitter amplifier, and also is needed to limit the current through the LED. C7 and R5 will limit the time that the trigger input of the timer keeps a low voltage, since the timer won't start until this input is high again. C5 is connected across pin 8 and ‘null’ inputs (pin 1) of IC1, and is probably for phase compensation or gain control.
XuFyaN
in this circuit I've found out the function of every component except R4, R5 and C4,C7 and C8 ...
can anybody please explain the purpose of R4, R5 and C4,C7 and C8 ?

also the Capacitor C5 (47pF) is connected across pin 8 and ‘null’ inputs (pin 1) of IC1 for phase compensation and gain control to optimize the frequency response,
what does it mean by phase compensation ? and why the collector is connected with R4 and C7 ?

and what will be the effect on circuit if i remove C5 or C2 from it ??

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I don't really know what the left side of the circuit does. C1 and C3 seem to form a potential divider that will throw away 999999/1000000 of the input signal. (since the non-inverting input of the opamp sits at 0.52 V.

R4 however is the collector resistance of a common emittor amplifier, and also is needed to limit the current through the led.

C7 and R5 will limit the time that the trigger input of the timer keeps a low voltage, since the timer won't start until this input is high again.

What kind of signal is this circuit supposeed to receive?

the circuit is sensing the frequency radiation of mobile phone through C3 (as mentioned in report)
actually C3 is acting as an antenna you said C3 is used as potential divider ?
and capacitor C5 is connected across pin 8 and ‘null’ inputs (pin 1) of IC1 , i don't know the reason :S why it is connected there :S

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From a data sheet the CA3130 has a maximum frequency of 15 MHz and in this circuit it would be a lot less than that.
You can get a data sheet here:
http://www.datasheetcatalog.org/datasheet/intersil/fn817.pdf

If you look at the input of this chip here:[PLAIN]http://dl.dropbox.com/u/4222062/CA3130.PNG

You can see some diodes at the input that may function as rectifiers at 900 - 5000 MHz which is the sort of frequency used by cell phones. This might give you some signal reception at very close distances.

The 555 here is used as a monostable. If its input is pulled low, the output will go high and produce sound from the buzzer for a time determined by R6 and C9.

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## 1. What is the purpose of a resistor in a circuit?

A resistor is an electrical component that is used to limit the flow of current in a circuit. This is important because it helps to protect other components from damage and also allows for the control of current and voltage levels within the circuit.

## 2. How do resistors and capacitors differ in their function in a circuit?

Resistors limit the flow of current, while capacitors store and release electrical charge. In a circuit, resistors are used for controlling current and voltage, while capacitors are used for filtering, smoothing, and storing electrical energy.

## 3. How are resistors and capacitors connected in a circuit?

Resistors and capacitors can be connected in series or parallel in a circuit. In series, they are connected one after the other in a single path, while in parallel, they are connected side by side, creating multiple paths for current to flow through.

## 4. Can a resistor and a capacitor be used together in a circuit?

Yes, resistors and capacitors are often used together in circuits to achieve specific effects. For example, a resistor can be used to limit the current going into a capacitor, preventing it from charging too quickly. They can also be used in combination for timing circuits or frequency filters.

## 5. How do I calculate the resistance and capacitance values needed for a circuit?

The resistance and capacitance values needed for a circuit can be calculated using Ohm's Law and the capacitor charge equation. It is important to consider the desired current and voltage levels, as well as the specific properties of the components being used, when determining the appropriate values for a circuit.

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