# Block Diagram and Circuit – Assignment Example

The paper "Block Diagram and Circuit" is an excellent example of an assignment on physics. The input voltage range supplied is 2 V to +9 V with a current of 25mA. This means that there is enough voltage, make the system work. The following equipment is required to come up with a circuit that is effective and that gives the right results during testing. The block diagram of the circuit that is being used The Power supply will help in supplying the current that is required to run the circuit. The switch will be in form 555 as a monostable circle this will help in the trigger circuit is connected to the switch button that activates the oscillator when pressed momentarily.

The trigger is designed such that when the user presses a button momentarily, the trigger signal lasts for 5 seconds. About 800Hz Oscillator (555 as an astable circle): this part is responsible for producing an audio frequency that is connected to the speaker. The oscillation produced from this part is a square wave at about 800 Hz frequencies. The 8 Ω speaker is the transducer from electrical energy to sound energy.

An ac signal is necessary for proper output in the speaker. The connection should also consider the current limitations of the oscillator circuit. The parts of the circuit Parts: R1, R2,R3, R4_______________ ResistorsC, C2,C3_______________ Polyester CapacitorsD1_______________ 75V 150mA DiodeQ, Q2________________ 45V 100mA TransistorSW1________________ Switch To construct the circuit we will need to the following equipments, Digital multimeter of DC volts minimum: 0.2 V, AC volts minimum: 10 V Breadboard Minimum size about 640 holes, power source, DC power supply, Two ‘ Plugpacks’ , 9 V dc, 200 mA plus connectors, Hook-up wire To suit breadboard, A pair of wire cutters/strippers and a pair of smooth-jawed pointed pliers, signal diode, Bipolar Transistors BC549, Zener diode, Voltage regulators, Logic gates, Comparator LM339, Timers LM555, Mono-stable, Operational Amplifier, Power amplifier LM386, Resistors as required 1/4 watt, metal film, Capacitors as required Polyester film, up to about 1uF Electrolytic, from 1uF upwards (axial or radial). A high signal of 5 seconds duration was required hence the choice of resistors and capacitor values.

A monostable produces a high output for a fixed duration of time when manually triggered with a low input (USQ, 2011).

The ON time for the output pulse is calculated as below: TON ≈ 1.1 R1 C To attain a theoretical 5 seconds, possible values of R1 and C that could have been used are 47kΩ and 100μ F. The term 1.1 R1 C is an approximation and not an exact value therefore a Slightly higher value could yield a value less than theoretical in practice. T≈ 1.1*47k*100μ ≈ 1.1*47000*0.0001≈ 5.17≈ 5 seconds 47kΩ is a typical resistor available commercially. 100μ F capacitor is also available. The values required to achieve an exact 5 seconds cannot be obtained commercially EXT) - Photo evidence showing Circuit board & Measurement Move the rheostat to the short circuit position to measure the current generated and check to ensure the voltage is zero.

Record the results on the appropriate row on the datasheet. This will be the maximum current the panel can generate, therefore select a suitable setting for the ammeter to give a full-scale deflection slightly larger than this value. Open the open circuit switch and record the voltage and current in the appropriate row on the datasheet.

This will be the maximum voltage that the panel will generate. Close the open circuit switch. Increase the load applied to the panel by gradually twisting the knob on the rheostat. You should observe that the voltage starts to rise. Take readings of the current at the voltages indicated on your datasheet. CALCULATIONS The power of the system can be calculated as Current = 9v/1.3m = 70mA. This is a current across the circuit.   This is because the total resistors are two as shown in the diagram above of 1.2mΩ and 100kΩ. It takes 5 seconds for one tone to reach the nurse.

This means that the oscillation per flash is 5seconds per flash. The definitions of the period, frequency and angular frequency used in ac circuits are the same as for simple harmonic motion. The values of R1 and R2 cannot go below 1K so as not to destroy the IC chip with the excess current. (Maximum current for 555 timers is 200mA). The value of R2 should be kept as low as possible so that the duty cycle of the signal produced to be about 50%.

In the above design, R1=2.2K and R2=4.7K. These are typical nominal values of resistors available commercially. The frequency of the signal produced is given by The capacitor 150nF is also an available nominal value. The frequency produced was thus f=  = 874Hz   TEST          RESULTS-TIMING TABLE DIAGRAMS When testing the circuit that is connected to the speaker a connection intercom line the circuit to be tested.     Then it is switched on then a key is pushed to send a sound that is not amplified. Various tones are selected from the keys of the pad containing keys that are used to determine the tone that is not noise.

The result    is recorded below; Position in Circuit (Test point) Theoretical Value (volts or mA) Measured Value At the beginning 8.01 7.2 Resistor 1 2.12 0.33 Resistor 2 3.2v 2.3V At the end 4.29 3.54   From the results, the frequency obtained was slightly more than 800Hz. The reason is because of the design compromise due to component value limitation. However, the difference was not much. Moreover, the obtained frequency is very much within an audible range by the human ear. Conclusion (Observation/Recommendations The circuit is very important for people who are disabled when they won't pass a message to the nurses.

The remote control of the circuit will emit a signal when the led is on, this goes out as a sound that will be recognized by the nurse. Within the circuit, there is photo-diode the will detect signal coming from the button used by the disabled person. When switch one is on there is an emission of IR waves that will make light fall on the diode and it will be visible. This will allow the flow of current across the circuit. If light id not visible then we can say that the circuit is no functioning and should be rechecked. When the switch has been put off the current flow stops, the sound does not move to the speaker for the nurse to hear.

At this point, the potential difference across the resistor is equal to the emf. If the switch is on the current flow of 10 =E R/ flows are experienced. When there is a reduction of voltage across the circuit by switching on the LED then as the voltage drop across the battery increases, the voltage drop across the resistor decreases, and thus the current decreases.

Long after the switch is closed, the potential difference across the battery is nearly equal to the current is small (Holdsworth, 2000). The theoretical aspect of design and the practical results obtained did not differ much. It was however notable that practically, the design produced a triggered pulse of about 5.17 seconds and not the theoretical 5 seconds. The difference is accrued to arithmetic approximations used in theory. Terminal 5 of the 555 timers was not connected anywhere. Typically, the terminal should be connected to a high capacitor of about 100μ F to maximize voltage spikes during the high-low transition.

However, since the frequency is less than 1 kHz, the spike effect is negligible thus the capacitor can be overlooked. Resistors have a provision for value error. The overall error contributed by this factor to the design was however negligible. I have successfully constructed a basic circuit to be used by disabled persons to alert a nurse in case of anything in this project.