Wiring panel

Relays are often used as electrically controlled switches. Unlike transistors, their switch contacts are electrically isolated from the control input. On the other hand, the power dissipation in a relay coil may be unattractive for battery-operated applications. Adding an analogue switch lowers the dissipation, allowing the relay to operate at a lower voltage. The circuit diagram shows the principle. Power consumed by the relay coil equals V2/RCOIL. The circuit lowers this dissipation (after actuation) by applying less than the normal operating voltage of 5 V. Note that the voltage required to turn a relay on (pickup voltage)is usually greater than that to keep it on (dropout voltage).


In this respect the relay shown has specifications of 3.5 and 1.5V respectively, yet the circuit allows it to operate from an intermediate supply voltage of 2.5V. Table 1 compares the relay’s power dissipation with fixed operating voltages across it, and with the circuit shown here in place. The power savings are significant. When SW1 is closed, current flows through the relay coil, and C1 and C2 begin to charge. The relay remains inactive because the supply voltage is less than its pickup voltage. The RC time constants are such that C1 charges almost completely before the voltage across C2 reaches the logic threshold of the analogue switch inside the MAX4624 IC.


When C2 reaches that threshold, the on-chip switch connects C1 in series with the 2.5V supply and the relay coil. This action causes the relay to be turned on because its coil voltage is then raised to 5 V, i.e., twice the supply voltage. As C1 discharges through the coil, the coil voltage drops back to 2.5 V minus the drop across D1. However, the relay remains on because the resultant voltage is still above the dropout level (1.5 V). Component values for this circuit depend on the relay characteristics and the supply voltage. The value of R1, which protects the analogue switch from the initial current surge through C1, should be sufficiently small to allow C1 to charge rapidly, but large enough to prevent the surge current from exceeding the specified peak current for the analogue switch.

The switch’s peak current (U1) is 400mA, and the peak surge current is IPEAK = (VIN – VD1) / R1 + RON) where RON is the on-resistance of the analogue switch (typically 1.2 Ω). The value of C1 will depend on the relay characteristics and on the difference between VIN and the pickup voltage. Relays that need more turn-on time requires larger values for C1. The values for R2 and C2 are selected to allow C1 to charge almost completely before C2’s voltage reaches the logic threshold of the analogue switch. In this case, the time constant R2C2 is about seven times C1(R1 + RON). Larger time constants increase the delay between switch closure and relay activation. The switches in the MAX4624 are described as ‘guaranteed break before make’. The opposite function, ‘make-before break’ is available from the MAX4625. The full datasheets of these interesting ICs may be found at http://pdfserv.maxim-ic.com/arpdf/MAX4624-MAX4625.pdf

1993 VW Passat Engine Control Module, Automatic Control Unit, and Automatic Solenoid Electrical Wiring Diagram are shown in the following figure. It shows the connection and wiring between each parts and component of Engine Control Module, Automatic Control Unit, and Automatic Solenoid system of the vehicle such as the multi-function switch, fuse/relay panel, knock sensor, coolant temperature sensor, shift lock solenoid, starter interlock/back up lit relay,automatic control computer clutch shut off relay, automatic control unit, automatic solenoids, program switch, throttle position sensor, full throttle switch, idle switch, throttle valve potentiometer, ignition booster, distributor firing order, engine control module, carbon canister, cold starter, idle air control valve, evap emission on/off valve, and many more.

Electric guitars use coils (guitarists call them pickups or elements) to convert the vibrations of the strings into an electrical signal. Usually, a guitar has more than one element builtin, so that the musician can select with a switch which element or elements are used to generate the signal. Because of the differences in construction of the elements and the varying positions of where they are mounted, each element sounds different. The elements can be roughly divided into two categories. There are the so-called ‘single-coils’ and ‘humbuckers’. Single coil elements are elements that contain one core and coil for each string. Humbuckers can be regarded as two elements that are connected in series. Many humbuckers have four connections (actually two single-coils with two connections each).

These two individual coils are usually interconnected with fixed wiring so that they are always used in series. The circuit proposed here offers the possibility of using a hum-bucker with four connections in no less than four different modes, each of which having its own sound. The only things that have to be changed on the guitar are the wiring and the addition of a four-position switch. The latter requires drilling holes in the guitar of course, but if there is a control cover plate (along the lines of a Fender Stratocaster, for example) then it makes sense to put the switch there. This avoids the need for drilling holes in the wood while keeping an (expensive) guitar reasonably unmarred. The schematic shows what the various things look like, electrically speaking, before and after the multisound modification.

In the form of the LT1579 Linear Technology (www.linear-tech.com) has produced a practical battery switch with an integrated low-dropout regulator. In contrast to previous devices no diodes are required. The circuit is available in a 3.3 V version (LT1579CS8-3.3) and in a 5 V version (LT1579CS8-5), both in SO8 SMD packages. There is also an adjustable version and versions in an SO16 package which offer a greater range of control and drive signals. The main battery, whose terminal voltage must be at least 0.4 V higher than the desired output voltage, is connected to pin IN1. The backup battery is connected to pin IN2. The regulated output OUT can deliver a current of up to 300 mA. The LDO regulator part of the IC includes a pass transistor for the main input voltage IN1 and another for the backup battery on IN2.

The IC will switch over to the backup battery when it detects that the pass transistor for the main voltage input is in danger of no longer being able to maintain the required output voltage. The device then smoothly switches over to the backup battery. The open-drain status output BACKUP goes low to indicate when this has occurred. When neither battery is able to maintain the output voltage at the desired level the open-drain output DROPOUT goes low. The LT1579 can operate with input voltages of up to +20 V from the batteries. The regulator output OUT is short-circuit proof. The shutdown input switches off the output; if this feature is not required, the input can simply be left open.

High Quality, Discrete Components Design, Input and Tone Control Modules

To complement the 60 Watt MosFet Audio Amplifier a High Quality Preamplifier design was necessary. A discrete components topology, using + and - 24V supply rails was chosen, keeping the transistor count to the minimum, but still allowing low noise, very low distortion and high input overload margin. Obviously, the modules forming this preamplifier can be used in different combinations and drive different power amplifiers, provided the following stages present a reasonably high input impedance (i.e. higher than 10KOhm).

Main Module:

If a Tone Control facility is not needed, the Preamplifier will be formed by the Main Module only. Its input will be connected to some sort of changeover switch, in order to allow several audio reproduction devices to be connected, e.g. CD player, Tuner, Tape Recorder, iPod, MiniDisc etc. The total amount and type of inputs is left to the choice of the home constructor. The output of the Main Module will be connected to a 22K Log. potentiometer (dual gang if a stereo preamp was planned). The central and ground leads of this potentiometer must be connected to the power amplifier input.

Circuit diagram:

Main Module Circuit Diagram

Parts:
R1_____________1K5 1/4W Resistor
R2_____________220K 1/4W Resistor
R3_____________18K 1/4W Resistor
R4_____________330R 1/4W Resistor
R5_____________39K 1/4W Resistor
R6_____________56R 1/4W Resistor
R7,R10_________10K 1/4W Resistors
R8_____________33K 1/4W Resistor
R9_____________150R 1/4W Resistor
R11____________ 6K8 1/4W Resistor
R12,R13________100R 1/4W Resistors
R14____________100K 1/4W Resistor
C1_____________220nF 63V Polyester Capacitor
C2_____________220pF 63V Polystyrene or ceramic Capacitor
C3_____________1nF 63V Polyester or ceramic Capacitor
C4,C7__________47µF 50V Electrolytic Capacitors
C5,C6__________100µF 50V Electrolytic Capacitors
Q1,Q2__________BC550C 45V 100mA Low noise High gain NPN Transistors
Q3_____________BC556 65V 100mA PNP Transistor
Q4_____________BC546 65V 100mA NPN Transistor

Tone Control Module:

This Module employs an unusual topology, still maintaining the basic op-amp circuitry of the Main Module with a few changes in resistor values. A special feature of this circuit is the use of six ways switches instead of the more common potentiometers: in this way, precise "tone flat" setting, or preset dB steps in bass and treble boost or cut can be obtained. Tone Control switches also allow a more precise channel matching when a stereo configuration is used, avoiding the frequent poor alignment accuracy presented by common ganged potentiometers. Six ways (two poles for stereo) rotary switches were chosen for this purpose as easily available. This dictated the unusual "asymmetrical" configuration of three positions for boost, one for flat and two for cut.

This choice was based on the fact that tone controls are used in practice more for frequency boosting than for cutting purposes. In any case, +5dB +10dB and +15dB of bass boost and -3dB and -10dB of bass cut were provided. Treble boost was also set to +5dB +10dB and +15dB and treble cut to -3.5dB and -9dB. Those wishing to use common potentiometers in the usual way for Tone Controls may use the circuit shown enclosed in the dashed box (bottom-right of the Tone Control Module circuit diagram) to replace switched controls. The Tone Control Module should usually be placed after the Main Input Module, and the volume control inserted between the Tone Control Module output and the power amplifier input. Alternatively, the volume control can also be placed between Main Input Module and Tone Control Module, at will. Furthermore, the position of these two modules can be also interchanged.

Circuit diagram:

Tone Control Module Circuit Diagram

Parts:

R1,R7___________47K 1/4W Resistors
R2_____________220K 1/4W Resistor
R3______________18K 1/4W Resistor
R4_____________330R 1/4W Resistor
R5______________39K 1/4W Resistor
R6______________56R 1/4W Resistor
R8_____________150R 1/4W Resistor
R9______________10K 1/4W Resistor
R10,R16__________6K8 1/4W Resistors
R11,R12________100R 1/4W Resistors
R13____________100K 1/4W Resistor
R14______________1K5 1/4W Resistor
R15,R21,R22______4K7 1/4W Resistors
R17,R24,R26______8K2 1/4W Resistors
R18______________3K3 1/4W Resistor
R19______________1K 1/4W Resistor
R20____________470R 1/4W Resistor
R23,R25_________12K 1/4W Resistors
R27,R28__________4K7 1/4W Resistors
C1_____________220nF 63V Polyester Capacitor
C2_______________1nF 63V Polyester or ceramic Capacitor
C3,C6___________47µF 50V Electrolytic Capacitors
C4,C5__________100µF 50V Electrolytic Capacitors
C7______________10nF 63V Polyester Capacitor
C8,C9__________100nF 63V Polyester Capacitors
Q1,Q2_________BC550C 45V 100mA Low noise High gain NPN Transistors
Q3____________BC556 65V 100mA PNP Transistor
Q4____________BC546 65V 100mA NPN Transistor
SW1,SW2_______2 poles 6 ways Rotary Switches
Simpler, alternative Tone Control parts:
P1______________22K Linear Potentiometer
P2______________47K Linear Potentiometer
R29,R30________470R 1/4W Resistors
R31,R32__________4K7 1/4W Resistors
C10_____________10nF 63V Polyester Capacitor
C11,C12________100nF 63V Polyester Capacitors

Power supply:

The preamplifier must be feed by a dual-rail, +24 and -24V 50mA dc power supply. This is easily achieved by using a 48V 3VA center-tapped mains transformer, a 100V 1A bridge rectifier and a couple of 2200µF 50V smoothing capacitors. To these components two 24V IC regulators must be added: a 7824 (or 78L24) for the positive rail and a 7924 (or 79L24) for the negative one. The diagram of such a power supply is the same of that used in the Headphone Amplifier, but the voltages of the secondary winding of the transformer, smoothing capacitors and IC regulators must be uprated. Alternatively, the dc voltage can be directly derived from the dc supply rails of the power amplifier, provided that both 24V regulators are added.

Note:

If this preamplifier is used as a separate, stand-alone device, thus requiring a cable connection to the power amplifier, some kind of output short-circuit protection is needed, due to possible shorts caused by incorrect plugging. The simplest solution is to wire a 3K3 1/4W resistor in series to the output capacitor of the last module (i.e. the module having its output connected to the preamp main output socket).

Technical data:

Main Module Input sensitivity:

250mV RMS for 1V RMS output

Tone Control Module Input sensitivity:

1V RMS for 1V RMS output

Maximum output voltage:

13.4V RMS into 100K load, 11.3V RMS into 22K load, 8.8V RMS into 10K load

Frequency response:

flat from 20Hz to 20KHz

Total harmonic distortion @ 1KHz:

1V RMS 0.002% 5V RMS 0.003% 7V RMS 0.003%

Total harmonic distortion @10KHz:

1V RMS 0.003% 5V RMS 0.008% 7V RMS 0.01%

Source : www.redcircuits.com

Most LED driver circuits use a series resistor to control the current through the LED. For applications needing a few LEDs, this is optimal. However, for applications needing many LEDs, this becomes extravagantly inefficient and it is tempting to keep the voltage drop across the resistor as small as possible. That leads to poor control of the current. ICs such as the MM5450 and its relatives and the A6275 and its relatives provide constant current outputs so that the current through the LEDs is well controlled even though the voltage drop across the circuit doing the control is acceptably small. However, the difficulty with these circuits is that because they contain many constant current drivers crowded into a relatively small package, unless the supply voltage is small, they become too hot and can destroy themselves.


This problem is not easy to solve. The solution is to maintain a small voltage across each constant current source. In this circuit, this is accomplished by REG1, the LM317L, which provides a bias of about 1.5V ±5%. Each transistor works as an emitter-follower, presenting the A6275 inputs with about 0.9V. Vled, the LED supply voltage, needs to be high enough to ensure that there will be at least 0.5V across each transistor but it is safe to allow significantly more than this and the supply need not be well regulated. The transistors can be general purpose NPN types such as BC548 and a single LM317L will easily supply a total LED current of at least 1A. A6275s are made by Allegro.

It is a charge pump design. This is where a capacitor (electrolytic) is allowed to charge and is then raised higher and allowed to discharge into a load. The load sees a voltage that can be higher than the supply.