Easy Balanced Output Board For The Stereo DAC Circuit

Easy Balanced Output Board For The Stereo DAC Circuit. This add-on board is designed to provide a pair of balanced audio outputs for the High-Quality Stereo DAC (Digital to Analog Converter). Two 3-pin male XLR connectors are used for the new outputs and they can either replace or augment the existing unbalanced outputs without affecting their performance. Balanced audio is used in recording studios and on stage because of its improved noise immunity.

Picture of the project:

    

This is due to the fact that the signal is sent differentially (ie, as two signals 180° out of phase) and then converted to a single-ended voltage signal at the far end. If any noise is picked up in the cable, it affects the two out-of-phase signals equally so that when the signals are subsequently subtracted, most of the noise is eliminated.

Parts layout:

In addition, the DAC’s performance at the balanced outputs generally exceeds that of the unbalanced outputs, although only by a small margin. The signal-to-noise ratio, frequency response and channel separation are all better, although we measured a tiny bit more distortion from the balanced outputs. However, both levels are so low as to be almost negligible.

Circuit diagram:

Comparison chart:

Source : www.circuitsproject.com

Read more

Petrol Gas Switch For A Pajero circuit and explanation

My current vehicle, a Pajero, was modified for dual fuel - ie, petrol and gas. However, its necessary to run the vehicle on petrol at regular intervals to stop the injectors from clogging up. This simple circuit allows the vehicle to be started using petrol and then automatically switches it to gas when the speed exceeds 45km/h and the brake pedal is pressed. Alternatively, the vehicle may be run on petrol simply by switching the existing petrol/gas switch to petrol. You can also start the vehicle on gas by pressing the brake pedal while starting the vehicle. The circuit is based on an LM324 dual op amp, with both op amps wired as comparators. It works like this: IC1a buffers the signal from the vehicles speed sensor and drives an output filter network (D1, a 560kO resistor and a 10µF capacitor) to produce a DC voltage thats proportional to the vehicles speed.

Circuit diagram:

This voltage is then applied to pin 5 of IC1b and compared with the voltage set by trimpot VR1. When pin 7 of IC1b goes high, transistor Q1 turns on. This also turns on transistor Q2 when the brake pedal is pressed (pressing the brake pedal applies +12V from the brake light circuit to Q2s emitter). And when Q2 turns on, relay 1 turns on and its contacts switch to the gas position. Trimpot VR1 must be adjusted so that IC1bs pin 7 output switches high when the desired trigger speed is reached (ie, 45km/h). In effect, the speed signal is ANDed with the brake light signal to turn on the relay. The vehicle has been running this circuit for several years now and is still running well, with no further injector cleans required.

Author: J. Malnar - Copyright: Silicon Chip Electronics

Read more

For Bicycles Rear Light After Glow circuit and explanation

This article is of interest only to readers whose bicycle lights are powered by a dynamo. The laws on bicycle lights in the United Kingdom are stricter than in other countries and a dynamo is, therefore, a rarity in this country. From the point of view of traffic safety it is advisable (in UK obligatory) for cyclists to have the rear lamp of their bicycle to light even when they are at standstill. In principle, it is not very difficult to modify the existing rear light with afterglow: all this needs is a large enough energy reservoir. Since the after-glow is required for short periods of time only, a battery is not required: a large value capacitor, say, 1 F, is quite sufficient.

As the diagram shows, in the present circuit, the normal rear light bulb is replaced by two series-connected bright LEDs, D2 and D3. These are clearly visible with a current of only 6 mA (compared with 50 mA of the bulb). The current is set with series resistor R1. The LEDs are shunted by the 1 F capacitor, C1. Since the working voltage of this component is only 5.5 V, it is, in spite of its high value, physically small. An effective regulator is needed to limit the dynamo voltage adequately. Normal regulators cannot be used here, since they do not work at low voltages. Moreover, such a device would discharge the capacitor when the cycle is at standstill.

Rear Light After Glow Circuit Diagram

Fortunately, there is a low-drop type that meets the present requirements nicely: the Type LP2950CZ5.0. Of course, the dynamo output voltage needs to be rectified before it can be applied to the regulator. In the present circuit, this is effected by half-wave rectifier D1 and buffer capacitor C2. Diode D1 is a Schottky type to keep any losses low – important for this application, because the ground connection via the bicycle frame usually causes some losses as well. The value of buffer capacitor has been chosen well above requirements to ensure that C1 is charged during the negative half cycles of the dynamo voltage.

Read more

Simple Phase Shift Meter for Audio Frequency Signal

Simple phase shift measurement can be done by squaring both the measured and the reference, then compute the difference of the two signals. The accuracy of the circuit shown in the schematic diagram  below is 1% UP to 2000 cps.

This circuit is used in computers and for high speed analog instrumentation. Negative value for zero phase shift is indicated by the zero center DC ammeter, zero for 90′ phase shift and some maximum value for 180′ phase shift.

 Phase-Shift Meter for Audio Frequency Signal Circuit Diagram

Read more

Simple Loudspeaker Circuit For Telephone Circuit Diagram

This below circuit is a easy handsfree telephone receiver system.  This doesn’t have dialing circuit so, it’s not a total phone replacement  circuit, but it’s just only a loudspeaker system (i.e, phone  receiver,not dialer). This is a easy circuit with all parts easily  available, and without any complex I.C. It is made of just capacitors,  diodes, resistors, and transistors.  This circuit can be made within 70  rupees and it compromises of the following sections

 Loudspeaker Circuit For Telephone Circuit Diagram

 

Power rectifier and filter section 
This section is made of a simple bridge rectifier and a indicating power LED.

Voltage regulator section
This section is made upon transistor Sl100, which is a general purpose NPN transistor in metal package. That is used to regulate voltage at a level of 9+0.6=9.6V by a 9V zener diode.

Speaker output section
This section contains a high impedance speaker and two BC548 NPN transistor to amplify the signal from line, the input of the 548 transistor pair is fed with a linear or pot control of 10K for volume adjust.

Microphone input section

This section contains a condenser microphone (tablet) and two BC548 NPN transistor to amplify the signal from mic, the output of the 548 transistor pair is fed with a linear or pot control of 10K for volume adjust to the line.

Read more

Feather Touch Switches For Main

An ordinary AC switchboard contains separate switches for switching ‘on’/’off’ electric bulbs, tube lights, fans, etc. A very simple, interesting circuit presented here describes a feather-touch switchboard which may be used for switching ‘on’/‘off’ four or even more devices. The membrane or micro-switches (push-to-on type) may be used with this circuit, which look very elegant. By momentary depression of a switch, the electrical appliance will be ‘on’/‘off’, independently. To understand the principle and de-sign of the circuit, let us consider an existing switchboard consisting of four switches. One live wire, one neutral wire, and four wires for four switches are connected to the switchboard, as shown in the illustration below the circuit diagram.

Feather-Touch Switches For Main Circuit diagram:

Feather Touch Switches For Main Circuit Daigram

The switches are removed and the above-mentioned wires (live, neutral, L1, L2, L3, and L4) are connected to the circuit, as shown in the main diagram. The circuit comprises four commonly available ICs and four micro-relays, in addition to four micro-switches/membrane switches (push-to-on type) and a few other passive components. IC 7805 is a 5-volt regulator used for supplying 5V to IC2 and IC3 (7476 ICs). These ICs are dual J-K flip-flops. The four J-K flip-flops being used in toggle mode toggle with each clock pulse. The clock pulses are generated by the push-to-on switches S1 through S4 when these are momentarily depressed.

When a switch is momentarily depressed,its corresponding output changes its existing state (i.e. changes from ‘high’ to‘low’ or vice versa) . The outputs of flip-flops drive the corresponding relays, in conjunction with the four relay driver transistors SL100. The wires earlier removed are connected to this circuit. On the switch panel board, the micro-switches are connected, and under the board the connections are wired as suggested above. Relays RL1 though RL4 are 9V, SPST-type micro-relays of proper contact ratings.

The circuit may be expanded for six switches by using one more IC 7476, and an IC ULN 2004 which has an array of seven  Darling-tons for driving the relays. So two more micro-switches and relays may be connected in a similar fashion. This circuit can be assembled on a general-purpose PCB and the total cost should not exceed Rs 300. It is suggested that the circuit, after assembly on a PCB, may be housed in a box of proper size, which may be fitted on the wall in place of a normal switchboard. 

Author :D.K Kaushil - Copyright : EFY mag

Read more

Sound Operated Switch for Lamps Circuit Diagram

This inexpensive, fully transistorised switch is very sensitive to sound signals and turns on a lamp when you clap within 1.5 metres of the switch. One of its interesting applications is in discotheques, where lights could be turned on or off in sync with the music beats or clapping.

Sound-Operated Switch for Lamps Circuit Diagram

The condenser microphone senses the sound and converts it into electrical variations. The electrical signals are amplified by the two-stage direct-coupled (DC) amplifier formed by transistors T1 and T2 and fed to the switching circuit. The switching circuit comprises transistors T3, T4 and T5, which conduct only when the circuit senses sound signals. Transistor T5 supplies sufficient gate voltage to the triac to drive the 230V lamp.

The regulated 12V DC power supply for the circuit is derived from AC mains by using resistor R14, diode D1 and zener diode ZD1. The circuit can be assembled on any general-purpose PCB.

Soursed By: EFY: Author Pradeep G.

Read more

Rugged PSU For Ham Radio Transceivers

This rugged power supply is based on the popular LM338 3-pin voltage regulator. The LM338 is capable of supplying 5 A over an output voltage range of 1.2 V to 32 V with all standard protections like overload, thermal shutdown, over-current, internal limit, etc., built in. In this power supply, some extra protections have been added to make it particularly suitable for use with low to medium-power portable and mobile VHF/UHF (ham) and 27 MHz transceivers. Diodes D4 and D5 provide a discharge path for capacitors C1 and C2. Diode D8 protects the supply against reverse polarity being applied to the output terminals. Capacitor C1 assists in RF decoupling and also increases the ripple rejection from 60 dB to about 86 dB.


If junction R1-R2 is not grounded by switch S1A, transistor T2 starts to conduct, causing the regulator to switch to zener diode D7 for its reference voltage (13 V). The PSU output voltage will then be 12.3 V. Normally, T2 will be off, however, and the PSU output voltage is then about 8.8 V. The high/low switch is useful to control the RF power level of modern VHF/UHF handhelds. Transistor T1, a p-n-p type BC557, acts as a blown-fuse sensor. When fuse F1 melts, T1 starts to conduct, causing LED D6 to light. If, for whatever reason, the PSU output voltage exceeds about 15 V, thyristor THR1 is triggered (typically in less than a microsecond).

Such a high-speed ‘crowbar’ may look like a drastic measure, but remember that this kind of protection is required by digital ICs that will not stand much overvoltage. The crowbar, when actuated, will faithfully destroy fuse F1 rather than allow the PSU to destroy expensive ICs. The two LEDs on the S1B contacts not only act as ‘high/low’ indicators but also as power-on indicators which are turned off when the mains voltage drops below about 160 V. If you envisage ‘heavy-duty’ use of the PSU, then voltage regulator IC1 should be mounted on as large a heatsink as you can get. The minimum we’d say is an SK129 heatsink from Fischer (Dau Components).

Read more

Timer for Geyser Circuit Diagram

The circuit comprises a timer IC 555 wired as an astable multivibrator with adjustable time period of 15 seconds. The astable output after inversion by an inverter drives decade counters IC3 and IC4 (each IC 7490) connected in cascade.

 Timer for Geyser Circuit Diagram

The decade counters output is connected to decoders IC5 and IC6 (each IC 7442), respectively. The decoder outputs (Q8 outputs of IC5 and IC6) are fed to inverters and the inverter outputs, in turn, are fed to an AND gate. The AND output is connected to the reset pin of the astable multivibrator built around another timer IC 555 to sound the alarm. Now you can turn off the geyser.

A green LED (LED1) has been used as the power supply indicator. Switch on the timer and the geyser at the same time. When the alarm sounds, it means that the water in the geyser has heated up and can be used.You can assemble the timer circuit on a general-purpose PCB and install it near your bathroom so that both the timer circuit and the geyser can be switched on simultaneously.

After the siren sounds, if required, we can increase the time by another 22 minutes for geyser by resetting the circuit by pushing reset switches S1 and S2 momentarily. If you want to change the preset time of the geyser, the same can be easily done by combining appropriate outputs of IC5 and IC6 using DIP switches (S3 and S4) while keeping in mind IC5 outputs (Q0 through Q9) are spaced 15 seconds apart and IC6 outputs are spaced 150 seconds (2.5 minutes) apart.

Caution. Please note that the timer circuit has no connection with the geyser circuit. The geyser works off 220V AC, while the timer works off 5V DC.

 This timer circuit for geyser sounds an alarm after the set timing of 22 minutes when the water is heated up.

Author V. Gopalakrishnan

Read more