Diagram Diagosis

Most small internal-combustion engines commonly used in the model-building world use glow plugs for starting. Unfortunately, glow plugs have an operating voltage of 1.5 V, while fuel pumps, starter motors, chargers and the like generally run on 12 V. This means that a separate battery is always needed to power the glow plug. The standard solution is to use an additional 2-V lead storage battery, with a power diode in series to reduce the voltage by approximately 0.5 V. However, this has the annoying consequence that more than 30 percent of the energy is dissipated in the diode. Naturally, this is far from being efficient. The converter presented here allows glow plugs to be powered from the 12-V storage battery that is usually used for fuelling, charging, starting and so on.

A car battery can also be used as a power source. Furthermore, this circuit is considerably more efficient than the approach of using a 2-V battery with a series power diode. The heart of the DC/DC converter is IC1, a MAX 1627. The converter works according to the well-known step-down principle, using a coil and an electrolytic capacitor. Here the switching stage is not integrated into the IC, so we are free to select a FET according to the desired current level. In this case, we have selected a 2SJ349 (T1), but any other type of logic-level FET with a low value of RDSon would also be satisfactory. Of course, the FET must be able to handle the required high currents. Diode D1 is a fast Schottky diode, which must be rated to handle the charging currents for C2 and C3. This diode must also be a fairly hefty type. The internal resistances of coil L1 and capacitors C2 and C3 must be as low as possible. This ensures efficient conversion and prevents the components from becoming too warm. The resistor network R2/R3 causes 87 percent of the output voltage to be applied to the FB pin of IC1.

This means that an output voltage of 1.5 V will cause a voltage of approximately 1.3 V to be present at the FB pin. The IC always tries to drive the switching stage such that it ‘sees’ a voltage of 1.3 V on the FB input. If desired, a different output voltage can be provided by modifying the values of R2 and R3. When assembling the circuit, ensure that C5 and C1 are placed as close as possible to IC1, and use sufficiently heavy wiring between the 12-V input and the 1-5-V output, since large currents flow in this part of the circuit. A glow plug can easily draw around 5 A, and the charging current flowing through the coil and into C2 and C3 is a lot higher than this!

circuit diagram of burglar alarm using IC timer 555/556 is functioned as an alarm to prevent thief entering your house. The alarm would produce loud sound when a thin wire connecting resistor R1 with IC pin no 4 is broken. Thin fiber is used as the wire. The thinner the wire, the more responsive the alarm. This circuit needs 5-15V power supply, buzzer is used as a speaker. Here is the circuit schematic :

Parts list :

•     Resistor R1 : 10k
•     Resistor R2 : 68k
•     Resistor R3 : 1k
•     Polar capacitor C1 : 1uF/15 B
•     Capacitor C2-C3 : 0.01uF
•     IC Timer : NE555

Derived from the Two-wire Lamp Flasher design, hosted on RED Free Circuit Designs since 1999, this astonishingly simple circuit allows one or two powerful 12V 21W car bulbs to be driven in flashing mode by means of a power MosFet.
Devices of this kind are particularly suited for road, traffic and yard alerts and in all cases where mains supply is not available but a powerful flashing light is yet necessary.

Circuit Diagram:

Car Bulb Power Flasher  Circuit Diagram

 

Notes:

• Flashing frequency can be varied within a limited range by changing C1 value.
• As high dc currents are involved, please use suitably sized cables for battery and bulb(s) connections.

Source : www.redcircuits.com

A difficult problem in the design of conventional stereo tone controls is obtaining synchronous travel of the potentiometers. Even a slight error in synchrony can cause phase and amplitude differences between the two channels. Moreover, linear potentiometers are often used in such controls, and these give rise to unequal performance by human hearing. Special potentiometers that counter these difficulties are normally hard to obtain in retail shops. A good alternative is a control based on a rotary switch and a discrete potential divider. The problem with this that for good tone control more than six steps are needed, and switches for this are also not readily available. Fortunately, electronic circuits can remove these difficulties.

The analogue selectors used may be driven by mechanical switches, standard logic circuit or a microcontroller. The selectors used in the present circuit are Type SSM2404 versions from Analogue Devices, which switch noiselessly. Each IC contains four selectors, so that a total of eight are used. The step size is 1.25 dB at 20 Hz with a maximum of 10dB . The circuit can be mirrored with S1, which means that a selection may be made of amplification or attenuation of bass frequencies. The user can choose between attenuation only and extending the range by dividing R9. The control can be bridged by switch S2.

To prevent the output impedance of the circuit having too much effect on the operation of the circuit, the output impedance must be ≤ 10 Ω. Resistor R1 2 protects the circuit against too small a load. At maximum bass amplification at Ui n = 1 V r.m.s., the THD+N <0.001% for a frequency range of 20 Hz to 20kHz and and a bandwidth of 80kHz. The circuit draws a current of about 10 mA.

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