In nowadays there’s been an upward trend in designing circuits with IC (Integrated Circuit), many function needed to be realized by analog circuits in the old days but now can also be fulfilled by IC that it is more stable and convenient and easy to use in circuit design. But however, with rich analog circuit knowledge can bring you more advantage when you come across the challenging situation in your career. This sound control logic circuit is just composed of resistors, capacitors and transistors which has no any IC and it is ideal for you to learn about the knowledge of RC Network to filter certain frequency of sound wave and multistage amplifier circuit.
3 x 104 Capacitors
1 x 1μF Electrolytic Capacitor
1 x 103 Capacitor
1 x 47uF Capacitors
2 x 4148 Diodes
1 x LED
2 x Header Pins
1 x Microphone
4 x 9013 Transistors
3 x 2.2kΩ Resistors
1 x 470kΩ Resistor
1 x 47kΩ Resistor
2 x 4.7kΩ Resistors
1 x 470Ω Resistor
1 x 1kΩ Resistor
Step 1: Solder the Resistors Into the PCB
Resistors do not have polarity, just follow image 1 to 3 to solder the Resistors into the PCB. The corresponding position of each resistor on the PCB has the resistance value printed within the white rectangle area. Before inserting the resistors into the PCB you should make sure each resistor is in the correct place or the circuit won’t work properly. How to identify the resistance value of the resistor? There are two approaches to do so, one is to read the value from the color bands printed on its body and the other is to use a multimeter to test it out. But in this project, I highly recommend you to use the multimeter to measure it out that can save you a lot of time. If you would like to know how to read resistance value from the color bands please go to How to Read Color Codes from Resistors.
Step 2: Solder the Capacitors Into the PCB
Follow the image 4 to 6 to solder the 104 Capacitors and Electrolytic Capacitors into the PCB. Please note that electrolytic capacitors have polarity, the long leg should be inserted into the hole near the ‘+’ symbol on the PCB while the short leg near the white band should be inserted into the hole in the shadow area on the PCB. The 103 and 104 Capacitors have no polarity that no need to care about the direction.
Step 3: Solder the 9013 Transistors Into the PCB
The flat surface of 9013 NPN Transistors should be at the same side of the diameter of the semicircle printed on the PCB. To identify the model number of the transistor just need to read the number carved on the flat surface of the transistor, as shown in image 8.
Step 4: Solder the Diodes Into the PCB
Diodes have polarity, the black end marked with red circle in image 10 is connected to the negative end(Low Potential End).
Step 5: Solder the Header Pins and Microphone and LED Into the PCB
Solder the short end of the header pins into the PCB and leave the long end for outer connection. The white circle on the PCB should almost be fully covered with the microphone as shown in image 12. The LED has polarity that the long leg should be inserted into the hole near the ‘+’ symbol on the PCB. As of now the project has been finished.
Step 6: Analysis
This circuit is composed of two main sub circuits, the left side is two-stage common emitter amplifier circuit, the right side is bistable multivibrator circuit. The R1 and C1 to form a RC network to block the sound waves under about 1kHz. When there is a sound signal applied to the microphone, the input signal can be amplified by Q1 and Q2, as we know, the common emitter amplifier circuit causes about 180° phase shift for the input signal, so a negative output signal will be generated from the collector of Q2 and delivered to C5 and C6 that causes a reverse state to both of Q3 and Q4. For example, if Q3 is On and Q4 is Off, when the amplified signal delivered to C5 and C6, then Q3 changed into Off state, Q4 Changed into On state, the LED is On. When apply a sound signal to the microphone again, Q3 will be changed into On state, Q4 will be Off State, LED is Off. If no more sound signal applied to the microphone, the Logic State of the bistable multivibrator circuit will always keep the present state. To get the raw materials please go to Mondaykids Store.