electronic project schematics

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Some Electronic Project SchematicsCollected by Niranjan Hegde This contains hobby Electronic Circuit Schematics which we can build easily. And gives a much more knowledge on designing and building of the Electronic circuits.

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Collection ByNiranjan Hegde

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Nirus SOME ELECTRONIC PROJECT SCHEMATICS

Contents

1. Audio Signal Tracer ……………………………………………………………………………3 - 42. Touch switch/Contact switch……………………………………………………………..5 - 63. Color Sensor……………………………………………………………………………………….7 - 84. Touch Switch………………………………………………………………………………………9 - 105. A low Voltage Amplifier…………………………………………………………………….11- 146. 18W Car Stereo Amplifier Using HA13118 IC………………………………………15-18

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1. Audio Signal Tracer

This schematics function is to enable one to trace an audio signal through a maze of wires running around the house.

As shown in the schematic above, when a inductor coil L1 is brought near the wire carrying the audio signal, the audio signal will be induced into the coil and the signal is fed to the inverting input of op-amp IC1-a. It is then amplified by and the amplified output is fed to IC1-b iverting input. The second op-amp increases the signal level to drive a set of low impedance headphone, Z1.

The coil L1 is made by using a size #30 enamel coated copper wire wound on a 1.25 inch length of a 0.25 inch diameter ferrite rod. Use a turn of appoximately 80 to 100 turns. It can be located several feet from the circuit and connected it through a shielded cable.

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http://www.electronics-project-design.com/free-electronic-project-schematics.html

http://www.electronics-project-design.com/free-electronic-project-schematics.html


Parts List

The parts list is as shown below.

Source : Extracted from Popular Electronics Feb 1993, By Charles D. Rakes

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2. Touch Switch/Contact Switch

The main part of the Touch Switch Free Electronic Circuits are the two NAND gates of the 4011 Integrated Circuit which are connected as a flip-flop. Pins 9 and 13 are the ON and OFF contacts. The two gates are connected to the positive rail by the two 10M resistors. Shorting one of the gates with the ground rail by touching it (this is equivalent to connecting about 50K between the gate and ground) FLIPs the output to that state. Shorting out the other contact FLOPs it back.

The output of the flip-flop drives a transistor connected as a switch. It switches an LED and a relay. The relay is a 12V relay and commonly available SPDT type 240VAC can be used to switch ON or OFF a lamp or other electrical appliances. However, make sure that the current and voltage of the device are within the contact relay specifications. Connecting the two 1K resistors connects the other two NAND gates of the IC into the flip-flop and makes it much more sensitive to touch. The touch plate may in fact work with only the first two gates connected. But it will be much more sensitive with all four gates connected as a flip-flop.

Ensure that an isolating transformer is used when the power supply comes from the mains before being rectified to 12V DC for safety purposes. The schematic diagram of the circuit is as shown below.

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http://www.electronics-project-design.com/free-electronic-circuits.html





Parts List

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3.Color Sensor

Colour sensor is an interesting project for hobbyists. The circuit can sense eight colours, i.e. blue, green and red (primary colours); magenta, yellow and cyan (secondary colours); and black and white. The circuit is based on the fundamentals of optics and digital electronics. The object whose colour is required to be detected should be placed in front of the system. The light rays reflected from the object will fall on the three convex lenses which are fixed in front of the three LDRs. The convex lenses are used to converge light rays. This helps to increase the sensitivity of LDRs. Blue, green and red glass plates (filters) are fixed in front of LDR1, LDR2 and LDR3 respectively. When reflected light rays from the object fall on the gadget, the coloured filter glass plates determine which of the LDRs would get triggered. The circuit makes use of only �AND� gates and �NOT� gates.

When a primary coloured light ray falls on the system, the glass plate corresponding to that primary colour will allow that specific light to pass through. But the other two glass plates will not allow any light to pass through. Thus only one LDR will get triggered and the gate output corresponding to that LDR will become logic 1 to indicate which colour it is. Similarly, when a secondary coloured light ray falls on the system, the two primary glass plates corresponding to the mixed colour will allow that light to pass through while the remaining one will not allow any light ray to pass through it. As a result two of the LDRs get triggered and the gate output corresponding to these will become logic 1 and indicate which colour it is.

When all the LDRs get triggered or remain untriggered, you will observe white and black light indications respectively. Following points may be carefully noted :1. Potmeters VR1, VR2 and VR3 may be used to adjust the sensitivity of the LDRs.2. Common ends of the LDRs should be connected to positive supply.3. Use good quality light filters.The LDR is mounded in a tube, behind a lens, and aimed at the object. The coloured glass filter should be fixed in front of the LDR as shown in the figure. Make three of that kind and fix them in a suitable case. Adjustments are critical and the gadget performance would depend upon its proper fabrication and use of correct filters as well as light conditions

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4.Touch Switch

In this Electronic Design Circuits Touch Switch project, a CMOS quad 2 input NOR gate IC is used as a latching circuit to switch a LED ON and OFF by physically touching the ON metal plate or OFF metal plate. The CD4001BC integrated circuit is a monolithic complementary MOS (CMOS) IC that are constructed with N- and P- channel enhancement mode transistors. Its input are protected against electrostatic discharge with diodes to VDD and VSS.

The circuit below shows the

schematic diagram of the touch circuit of which the NOR gates are configured as a simple latching circuit. When the skin contact is made between contacts T1 and T2 or T3 and T4, the LED switches ON and OFF respectively. The latching circuit is to ensure that the output will not fluctuate between ON and OFF. When the T1 and T2 contacts are bridged through the skin contact, the output of U1-a will go to logic "0" and caused the output of U1-b to go to logic "1". This output will in turn caused NOR gate U1-c to go to logic "0" causing transistor Q1 to turn ON, and hence LED will turn ON. The circuit will remain latched with the LED ON until contacts T3 and T4 are bridged of which the output of U1-a will go to logic "1", output of U1-b will go to logic "0", output of U1-c will go to logic "1" and the transistor Q1 will turn OFF. The LED will then turn OFF. It is important to ensure that 9V battery

is used as its DC source. If one uses the mains supply to step down the voltage using a transformer for rectification and filtering to get the 9V DC supply, ensure that the transformer is designed in such a way that it follows the safety standard requirement of UL. This is important to ensure the safety of the user that is using the metal contacts to ON/OFF the LED.

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http://www.electronics-project-design.com/Electronic-Design-Circuits.html

http://www.electronics-project-design.com/Electronic-Design-Circuits.html


Parts List

5. A low voltage preamplifier (Optimised for 3V operation)

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Description:This is a special low voltage version of my audio preamp. T1's emitter voltage is biased close to half supply voltage (1.5V) to allow for maximum output voltage swing. Both transistors are direct coupled and have closed loop feedback to aid temperature stability.

T2 realizes the amplifiers full voltage gain, and for low noise operation, T2 collector current is about 70uA. T1 merely buffers T2 and operates in emitter follower mode providing a good low output impedance. The overall S/N ratio measured at the output is shown below:

Signal to Noise Ratio

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Capacitor C3 decouples the emitter resistor of T2. Without C3 the gain of T2 would be approximately R1 / R4. With C3 the gain of T2 is now R4 in parallel with the input impedance of T1 / the small signal emitter resistance of T2. The overall voltage gain of the circuit is around 28 times as shown below. Harmonic distortion is about 8%.

Harmonic Distortion

Frequency response is flat from 50Hz to around 200KHz. Phase change across this range varies little, see bode plot below.

Bode Plot

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One drawback of this circuit is that the input impedance is fairly low. This is because the input of T2 is low and has C3 decoupling the emitter. The inclusion of R7 in series with the base of T2 raises input impedance slightly. A plot of input impedance versus freqency response is shown below.

Input Impedance

The output impedance is very low, around 66 ohms as shown in the plot below. Note that this is a preamp and therefore designed to feed into a power amplifier not drive direct loads directly.

Output Impedance

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6. 18W Car Stereo Amplifier Using HA13118 IC

This car stereo amplifier project is a class AB audio power amplifier using the Hitachi HA13118 module. It not only can be used in car application but also in any portable or home amplifier system. It is easy to construct and has a minimum of external components. The module has a high power output from a low voltage supply using the bridge tied load method, and a high gain of 55dB.

This project will be especially useful in applications where the input signal is a low level, without requiring the use of a separate pre-amplifier. This IC module has a built in surge protection circuit, thermal shut down circuit, ground fault protection circuit and power supply

fault protection circuit making it extremely reliable.

The Specifications of this project are:

D.C. Input : 8 – 18V at 1-2 A

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http://www.electronics-project-design.com/CarStereoAmplifier.html



Power output : 18W maximum, 4 ohm load, 18V DC supply

S/N ratio : > 70 dB

THD : < 0.2% @ 1W

Freq. Response : ~ 30 Hz to 30 kHz, –3 dB

Input level : < 25 mV, for full output (G > 50dB)

Input Impedance : ~ 30 k ohm

The supply voltage required for this project is 8 -18V DC, at least 1 to 2 Amps. Maximum output power will only be obtained with a power supply of 18V at greater than 2 A, using a 4 ohm speaker. The power supply should be well filtered to reduce mains hum, a regulated supply will reduce noise even further. Extra filtering is unnecessary if operating from a battery supply.

Circuit Diagram Description

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Most of the circuitry is contained within the amplifier module. C10 is the input coupling capacitor and blocks DC from the input. C11 bypasses any RF which may be present at the input. C1 & C2 provide an AC ground for the inverting inputs of the IC. R1/C7 and R2/C8 provide a high frequency load for stability with difficult speakers. C5 and C6 provide “bootstrap” feedback for the IC. C9 and C12 provide power supply filtering.

An externally mounted logarithmic potentiometer of between 10k ohm and 50k ohm, is used depending on the desired input impedance. The impedance should be keep as high as possible for a guitar amp, unless using a separate pre-amp. Make sure that the heat sink is mounted to the module.

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Parts List

You may download the full data sheet for the the Car Stereo Amplifier HA13118 here.

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http://www.electronics-project-design.com/support-files/ha13118.pdf


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