Digital Voice Record and Playback Project

This project is based on ISD2560P IC which allows you to record 60 seconds voice and then playback it with very high quality.

 

 As shown in the schematic, the input soruce is an electret microphone. If a dynamic microphone is used, R2,R3,R4 resistors and C3,C5,C7 capacitors will be omitted and microphone will be connected to the 17 and 18 numbered pins directly. Since it has better frequency response, we choose electret microphone in this project.

 

Controlling the circuit is very simple. Sw1 switches between record and playback modes. Push button B1 is used for start and pause functions. B2 stops the process.

To record voice, first move Sw1 to the record position and then push B1 once. IC will start recording and during this process red LED will bright. One push to B1 pauses and second push continues recording. You can record 60 seconds by this way. To stop recording push B2.

To listen the voice recorded before, move Sw1 to playback position then push B1. During the playback process red LED will bright again. One push to B1 pauses and second push continues playing. To stop playback push B2.

There are some other operating modes for ISD2560P. Mode choice is done by the 7 numbered pin of the IC. For instance if you want to play the voice repeatedly, 7 and 4 numbered pins must be connected to +5V. Another mode is recording and playing only during pushing B1 button. To switch this mode, connect the only 6 numbered pin to +5V.

Supply voltage of the circuit is +9V that is supplied by a 9V battery or 9V AC/DC adapter.But since ISD2560P requires +5V, we use a voltage regulator in our circuit. You can see the supply part of the circuit based on 7805 regulator in the figure.

 

SD2560P IC includes an amplifier to drive a 16 OAmplifier Parthm speaker but the output volume is not sufficiently enough. So instead of a 16 Ohm speaker, an amplifier circuit must be connected to the output. You can see the amplifier part of the circuit based on LM386 in the figure. SP+ and SP- pins must be connected to 14 and 15 numbered pins of ISD2560P. A 100K potentiometer is used to adjust the output volume. If the output of the amplificonnected to a 8 Ohm speaker, then much higher volume will be taken. 

300 Watt MOSFET Real HI-FI Power Amplifier

My passion for excellence progressed over the past 40 years to developing sonically superior amplifiers to the highest possible standards, providing life like sound performance.

I am committed to sharing my experience of the RAS 300 with other enthusiasts sharing my passion for perfection.I designed this minimalist amplifier to be durable, simple to operate while offering high fidelity equivalent to the original sound source and would recommend partnering this amplifier only with other products of outstanding quality.

When I set out to design this amplifier, my aim was to create a product most suitable for the reproduction of complex music and speech signals. Although I placed high emphasis on electrical characteristics, the single most important requirement is achieving an audibly superior sound, vivid spatial imaging and superb tonal clarity.

Although the average listening level is normally less than 10 watts, my design approach was to create an amplifier with ample reserve power, but biasing it for class A at average listening levels reducing cross-over distortion to extremely low levels.

There is not one capacitor in the signal path, improved the accuracy of the tonal characteristics of instruments and voices significantly.
The RAS 300 has almost zero phase distortion far beyond the audio range resulting in perfect resolution and totally un-coloured sound.

Amplifier Specification:
Maximum Output: 240 watts rms into 8 Ohms, 380 watts rms into 4 Ohms
Audio Frequency Linearity: 20 Hz – 20 kHz (+0, -0.2 dB)
Closed Loop Gain: 32 dB
Hum and Noise: -90 dB (input short circuit)
Output Offset Voltage: Less than 13 mV (input short circuit)
Phase Linearity: Less than 13 0 (10 Hz – 20 kHz)
Harmonic Distortion: Less than 0.007% at rated power
IM Distortion: Less than .009% at maximum power

The amplifier consists of two completely separate monaural amplifiers each channel has its own power supply, resulting in zero inter-channel cross talk, a common phenomenon in amplifiers sharing the same power supply.

In order to obtain the full output power each supply transformer should be rated at 40VAC – 0 – 40VAC at 640VA. Unlike many designs relying on the reservoir capacitors to supply peak currents, I prefer to have the raw power available from the transformer resulting in much faster transients.

Although the RAS 300 specifications are moderate, when listening to it you will immediately experience the massive reserve power available and never have any cause of anxiety that something is going to give in that one would when driving many amplifiers loud.

You will hear nothing but reality with no distortion at any level and I guarantee that this amplifier will divulge the best qualities of any equipment connected to it.

Electronically Controlled Security Door Keyboard

The circuit was constructed to provide a simple electronic lock system based on a single integrated circuit and will require a code of seven digits.

• 4022 – a 4-stage CMOS counter with 8 decoded outputs used for binary counter/decoder, divide-by-N counting, frequency division, decade counter/decimal decode display, and counter control/timers due to its features such as standardized symmetrical output characteristics, medium speed operation, parametric ratings (5V, 10V, 15V), 100% tested for quiescent current at 20V, and fully static operation
• BS170 – an N-channel enhancement mode field effect transistor designed to minimize on-state resistance while providing reliable, rugged, and fast switching performance and particularly suited for low voltage, low current application such as power MOSFET gate drivers and small servo motor control due to its features of high saturation current capability, voltage controlled small signal switch, and high density cell design
• BD679 – a monolithic NPN Silicon epibase power Darlington transistor with resistors and diode in a TO 126 plastic package and is typically used for AF applications due to its high current gain

The construction of the circuit is relatively simple since it utilizes a very few components. One important thing to be considered in doing this circuit is the time it will take, after the push button switches are pressed, for the code to reach the main IC. There will be a delay unless all the keys were entered. When the right sequence of code was entered correctly, the output of Q7 will be activated for approximately 4 seconds. This will drive the transistor Q2 which in turn would drive one relay that will open the door or any other circuit attached.

The use of red LED D3 provides a visual indication of the activation of Q2. The code that has been set for the circuit is 1704570, as seen in the diagram. This was made possible by the arrangement of the resistors with their corresponding connections to the switches. The resistors are arranged from points A to G order while the switches are connected to the corresponding resistors in random order. The security code can be changed by altering the connections between the switches and the outputs of the IC1.

In most secured places with the capability of the company to purchase high end equipments, an electronic key operated door is usually installed. This will prohibit the entry of unauthorized persons or verify the entrance of a person by supplying the correct key code. This electronic security door key may also be found on vehicle doors for locking and unlocking purposes. Other establishments that utilize this are jewelry shops, banks, apartments, factories, hotels, prisons, apartments, and homes. They are very reliable since they are convenient to use and can be integrated easily with other circuitries.

12V Lead Acid Battery Discharge Indicator

The circuit was designed to produce an indication before a 12 V lead acid battery would reach the discharged state

• LM723 – a positive NPN standard voltage regulator mainly designed for series regulator applications which can be utilized for both foldback and linear current limiting due to its very low standby current drain circuit
• Trimmer – a miniature variable component used to make fine adjustments to capacitance, inductance or resistance (potentiometers)
• BC547 – NPN small signal transistors designed for general purpose switching and amplification due to its low voltage, low current and three different gain selections

Lead acid batteries are comprised of a Sulphuric acid solution electrolyte, a sponge metallic lead anode and a lead dioxide cathode. Because of the chemical combinations, this heavy metal element is toxic and disposing it improperly would be hazardous to the environment. Mechanically, the lead acid battery is made of a series of identical cells where sets of positive and negative plates comprise each cell. A typical cell is built with more plates in order obtain the needed current output. The positive plates are attached together as well as the negative plates. There are always one or more negative plates than positives because the arrangement of the positive plate is always in between the negative plates. These plates are immersed in an electrolyte of dilute sulphuric acid and distilled water. Sulphuric acid is a very reactive substance of oxygen atoms, sulphur, and hydrogen. The sulphuric acid has the ability to distribute itself very evenly throughout the electrolyte in the battery due to its instability. This will always to an even reaction between all the plates by producing current and voltage. Both plates are turned into lead sulphate by the chemical reaction between the lead dioxide at the positive plates, the spongy lead at the negative plates, and parts of the electrolyte.
The result of all the reaction is a potential difference between the two plates where the positive plate gives up electrons and the negative plate gains them in equal numbers. However, there is a limitation in the length of time for the reaction to produce the cell voltage. The voltage will remain constant without the presence of connection between the two plates. The chemical reaction will be able to continue the electrons to flow through the circuit from the negative plate to the positive in the event that a load is placed between the positive and negative plates. The current produced by the cell is represented by the flow of electrons. The battery will fail to produce any current when the supply of electrons becomes depleted. The cause of this depletion may pertain to the electrolyte being turned mostly into water or the active material on the negative plate has been used up. The efficiency of the battery system depends on the heating levels of the chemical process wherein greater heating means the battery is quickly exhausted.
To protect the batteries for the fear of being destroyed, the circuit provides the detection of discharge. Since the lead acid battery has a voltage of 12 V, it is not allowed to be rated below 10.8 V. otherwise, the LED would light to indicate the voltage drop. Lead acid batteries should never run flat and the maximum recommended discharge is 75% of the total. This signifies that the minimum charge remaining on the battery should be around 25% before recharging. Lead acid batteries should always be regularly charged even on its idle state once it has been filled with electrolyte. Due to its own resistance, the battery is self discharging when not in use. This could lead to a flat discharge even without putting the battery into service. The self discharge rate is a measure of how much the batteries discharge by them and is managed by the metallurgy of the lead used inside and the construction of the battery. The depth of discharge is a measure of how deeply the battery is discharged. The deeper the batteries are discharged, the shorter is their life cycle.
On order to control the discharge of the battery, a stable voltage in a circuit is required to check the voltage. This can done using the IC1 LM723 which is a monolithic integrated circuit programmable voltage regulator, assembled in 14-lead dual in-line ceramic and plastic package. It can provide internal current limiting and an external NPN or PNP pass element may be used when the output current exceeds 150 mA. The specifications are made for remote shutdown and adjustable current limiting. The poles of the battery are connected to the terminal entry of the circuit. The stability voltage around 7.15 V is handled by the pin 6 of the IC as it receives an input voltage larger than 9.5 V. the stability voltage is provided to the pin 5 while pin 4 obtains a part of the input voltage which is checked by the trimmer. The trimmer is meant to be set correctly when installed. IC1 operates as a voltage comparator which compares the value of voltage between pin 4 and pin 5. When the voltage in pin 4 is larger than the voltage in pin 5, the output in pin 9 becomes low. But when the output in pin 9 becomes high, the LED will turn on as a result of the conduction of Q1. The regulation of the circuit requires an external power supply which can be regulated with a value of 10.8 V. the trimmer is also adjusted so that when the LED turns ON, the voltage from the supply will be improved.
The rate of discharge is also affected by storage. A battery should never be stored directly on the ground especially not on the concrete. Using wooden pallets is the best storage method since it will not allow damp paths, will not conduct, and will provide good air circulation. A refreshening charge once every two months or more is recommended by most manufacturers during storage. Thin electrode plates allow a lot of energy to be discharged quickly for a short period of time like in car batteries. Thick electrodes in lead acid batteries can tolerate discharges better than thin but at the expense of producing heavier batteries.
Lead acid batteries are being used in several industries because they are tried and tested, robust, tolerant to abuse and overcharging, low internal impedance, can deliver high currents, wide range of capacities and sizes, supplied worldwide, indefinite shelf life if stored without electrolyte, reliable, and low cost. They are used in equipments like the electrical motors in conventional submarines and nuclear submarines where large lead acid batteries are used; in power failure cases which use lead acid batteries for emergency lighting; in uninterruptable power supplies used for small computer systems, marine applications, electric scooters, and electrified bicycles where backup power supplies for alarm are utilizing gel batteries; in supplying heater voltage in the early radio receivers constructed out of vacuum tubes; in providing large backup power supplies for computer centers and telephone, off-grid household electric power systems, and grid energy storage where wet cell batteries are employed which is designed for deep discharge; in battery electric vehicles like golf carts which use propulsion batteries; in forklifts where batteries are used as counterweights; and in motor vehicles for ignition, lighting, and starting where the current for initiating internal combustion engines are provided by batteries.

Nickel-Cadmium (NiCd) Battery Charger

The circuit diagram shows a regular charger being powered by an AC input source, intended for charging batteries.
This type of rechargeable batteries are usually termed as “NiCd”, which was a brand name of SAFT Corporation and should not pertain generically to nickel-cadmium batteries. Charging NiCd batteries requires constant current source by using a transistor. The BD140 power transistor has the features of high current (max. 1.5 A) and low voltage (max. 80 V). It is generally used for power applications purposes as used in television circuits and hi-fi amplifiers. Two high conductance fast diode 1N4148 applies a direct voltage to the majority-carrier of the transistor while stabilizing the voltage drop across them. Voltage drop can be defined as the reduction in voltage across a conductor where current is flowing. When the switch is closed, the charging current is estimated as 15mA to 45mA which makes it appropriate for rechargeable batteries of 1.5 V and 9 V. For high quality NiCd’s, the charging stops when the battery gets too hot. To obtain the best results, charging should be done in a room temperature or cool place. The discharge rate for NiCd batteries depends on the size.
There are other available types of rechargeable batteries in the market. While NiCd uses nickel oxide hydroxide and metallic cadmium as electrodes, the nickle-metal hydride cell (NiMH) uses hydrogen-absorbing alloy for negative electrode. The Lithium-ion (Li-ion) uses the anode, cathode and electrolyte to function properly.
The disdavantage of NiCd batteries is the severe toxicity and high cost. Inaccurate use of these batteries can lead to damage to itself or to humans.

Digital Voltmeter with 3-Digit Output

The construction of the device uses PIC16F676 for reading analog signal such as voltage, and displaying the 3-digit output by using 7-segment LED.

On the hardware part, the PIC16F676 has 10-bits 8 channels since most of PIC microcontrollers has either 8-bit or 10-bit analog to digital converter module. In this project, only one channel is used for measuring the input voltages while the others pins are used for digital I/O. A voltage divider consisting of R1 & R2 is used for the voltage input. The appropriate display of full scale voltage is being adjusted by VR1 connected in parallel with R2. The analog input will come from the divided input voltage from AN3.
In scan display routine, the digital output RA0-RA2 turns ON/OFF the digits. The 7-segment display is driven by the RC0-RC5 and RA5 and will be decoded by a software using CCS C compiler to programming. The 7-segment code is a converted form of the input voltage on RA3. The interrupt of every 5 ms is set on the timer while scanning all digits around 66 Hz frequencies. This means that for every 5 ms, only one digit is turned ON

1A Power Supply with 0 to 15 Volts Adjustable Output

Terminology

2N3055 – a complementary Silicon Epitaxial-Base planar NPN transistor mounted in Jedec TO-3 metal case for use as power transistor
Bridge Diode – also known as bridge rectifier which has four diodes arranged in a bridge configuration where the output voltage has the same polarity with either polarity of the input voltage
The construction of this power supply circuit is very simple in such a way that the components used are easy to be located while the cost is very cheap. With the biggest provided current at 1 A, the output voltage is adjusted for minimal ripple effect and stabilized in the range of 0 V to 15 V DC. This is made possible by the standard transformer output of 1.5 A with a primary winding voltage of 220 V and secondary voltage of 18 V. The current is being limited by the Zener diode D1 with a rating of 18 V and 1.5 W. The linear potentiometer R2 is responsible for the regulation of current.
The power transistor Q1 is a classic type that would require to be placed in a suitable heatsink to suppress the high heat dissipation during the operation of the circuit. The heat dissipation will be continuous during the presence of the highest current. The bridge diode GR1 will provide full wave rectification from the AC input which will also convert the incoming alternating current (AC) input into direct current (DC) output. One good feature of the bridge diode is maintaining the same polarity of the output regardless of the polarity of the input.

The 15V/1 A power supply may be used to handle home automation control system which can be powered by 12 Vdc. They can be made into power adapter models to support a wide variety of applications such as TFT monitors, broadcasting, laptops, digital cameras, telecommunications, PSP’s, routers, notebooks, guitar effects pedals, KVM extenders, iPod’s, scanners, CCTV’s, printers, cassette players, radios, and other portable applications.