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A question recently asked on the Elektor website forum was how to make several white LEDs ‘sparkle’. The helpful author has not only provided a useful suggestion (use a random effect), but also devel-oped a suitable circuit and even designed a PCB layout. You can download the Eagle files for this from the Elektor website page for this article (www.elektor.com, archive # 080329-1.zip).

But first let ’s consider the basic question: artificial sparkling or glittering can best be simulated by having the different light sources switch on randomly at a par ticu-lar frequency. Surprisingly enough, it is not all that easy to generate truly random se quencesele ctronically. However, the electronic ran-domness does not necessarily have to be perfect for glitter applications. Patterns that appear to be random are suf-ficient for the desired visual impression.

Based on this principle, the author uses two 556 timer ICs to generate signals whose frequencies (850 Hz for IC1a and 180 Hz for IC1b) can be divided by each other with-out yielding an integer divisor. A decimal counter oper-ated in an unconventional manner uses these two signals to produce a constantly pseudo-random pattern on its ten outputs, which repeats itself only very infrequently. This behaviour is obtained by applying the higher frequency signal to the CLK input of counter IC2, with the CLK Inhibit input on pin 13 being driven by the lower-frequency signal. The result is ‘genuine pseudo-random’ blinking.

LEDs can be connected directly to the ten outputs, since a CMOS output can anyhow only supply a few milli ampères. However, it is recommended to use series resistors (2.2 kΩ to 4.7 kΩ) to reduce the load on the IC out-puts if the supply voltage is higher than 10 V. If you want to have more than ten LEDs glitter, you can naturally build several copies of this circuit.

Author : Hans-Jürgen Zons - Copyright : Elektor

Simple Light Chaser I Circuit Diagram. Chase lights (or chaser lights) are often associated with the marquee signs of some movie theaters, and have also been used as a common element of television. Light Chasers is an album by Cloud Cult.In this schema Up to 100 lights, LEDs, or optocoupler triac diagram can be sequentially activated by this schema. One (Ul) 4017 decode counter sequences 10 LEDs whose common anode is returned through a second (U2) CD4017, which counts at one-tenth of the rate. The flash rate is controlled by U3, a clock schema, with a 555 timer. View:  Artificial random Simulated Flicker Sequencer Circuit Diagram

For a collector follower with emitter resistor, you’ll often find that the gain per stage is no more than 10 to 50 times. The gain increases when the emitter resistor is omitted. Unfortunately, the distortion also increases. With a ubiquitous transistor such as the BC547B, the gain of the transistor is roughly equal to 40 times the collector current (Ic), provided the collector current is less than a few milliamps. This value is in theory equal to the expression q/KT, where q is the charge of the electron, K is Boltzmann’s constant and T is the temperature in Kelvin.

For simplicity, and assuming room temperature, we round this value to 40. For a single stage amplifier schema with grounded emitter it holds that the gain Uout /Uin (for AC voltage) is in theory equal to SRc. As we observed before, the slope S is about 40Ic. From this follows that the gain is approximately equal to 40I cRc. What does this mean? In the first instance this leads to a very practical rule of thumb: that gain of a grounded emitter schema amounts to 40·I c·Rc, which is equal to 40 times the voltage across the collector resistor.

If Ub is, for example, equal to 12 V and the collector is set to 5V, then we know, irrespective of the values of the resistors that the gain will be about 40R(12–5) = 280. Notable is the fact that in this way the gain can be very high in theory, by selecting a high power supply voltage. Such a voltage could be obtained from an isolating transformer from the mains. An isolating transformer can be made by connecting the secondaries of two transformers together, which results in a galvanically isolated mains voltage.

10,000x With One Transistor Circuit diagram

That means, that with a mains voltage of 240 Veff there will be about 340 V DC after rectification and filtering. If in the amplifier schema the power supply voltage is now 340 V and the collector voltage is 2 V, then the gain is in theory equal to 40 x (340–2). This is more than 13,500 times! However, there are a few drawbacks in practice. This is related to the output characteristic of the transistor. In practice, it turns out that the transistor does actually have an output resistor between collector and emitter.

This output resistance exists as a transistor parameter and is called ‘hoe’. In normal designs this parameter is of no consequence because it has no noticeable effect if the collector resistor is not large. When powering the amplifier from 340 V and setting the collector current to 1 mA, the collector resistor will have a value of 338 k. Whether the ‘hoe’-parameter has any influence depends in the type of transistor. We also note that with such high gains, the base-collector capacitance in particular will start to play a role.

As a consequence the input frequency may not be too high. For a higher bandwidth we will have to use a transistor with small Cbc, such as a BF494 or perhaps even an SHF transistor such as a BFR91A. We will have to adjust the value of the base resistor to the new hfe. The author has carried out measurements with a BC547B at a power supply voltage of 30 V. A value of 2 V was chosen for the collector voltage. Measurements confirm the rule of thumb. The gain was more than 1,000 times and the effects of ‘hoe’ and the base-collector capacitance were not noticeable because of the now much smaller collector resistor. Link

This is a Simple Comparator with time out Circuit Diagram. The MC1422 is used as a comparator with input (Pin 5). The frequency of the pulses for the capability of a timing output pulse when the the values of R2 and Cl as shown is approx i-inverting input (Pin 6) is the non inverting mately 2 Hz, and the pulse width 0 ms.

Build a Simple Scr Replacing Latching Switch Circuit Diagram.This schema provides the tum-on characteristics of an SCR, but turns off with ease. The switch is comprised of three transistors with descending current ratings: Q3 has a high-current rating and Q2 has a medium rating. 

 The current, !1, to be switched is 15 A. Momentarily depressing S2 removes Ql`s base drive, turning Ql off and allowing Q2 to tum on. Q2 then drives the base-emitter junction of Q3, turning Q3 on. Q3`s collector-emitter voltage, which ·serves as Ql`s base drive, is essentially zero, keeping Ql off. To tum Q3 off, depress Sl; this action momentarily shunts Q2`s base current to ground, reversing the chain of events that turned Q3 on.

This schema sent out an alarm when its LDR sensor is exposed to light by sun or lamp. A 555 astable multivibrator was used here which sent signal a tone of about 1kHz upon detecting light.The sensor when exposed by light completes the schema and makes the 555 oscillate at about 1kHz with transistor to drive current.

The sensor is also shown in the schema diagram. It has to placed making an angle of about 30 – 45 degrees to the ground.

Sensitivity can be adjust with P1.  This makes the sun light to flow through it to the ground and prevents the alarm from going on due to the stored light on the sensor.

This is a simple voice activated or switch on schema diagram. With this sound activated switch, control by sound may be very useful, not just on a robot but also for a bit of home automation.This schema provides either latched switching or timed switching. U1A and UlB provide audio amplification from the microphone. U2 is a retriggerable monostable multivibrator. 

SI A and SIB select either U3, a flip-flop, or U2. R13 and R14 allow a 6- to 60-second timer delay after the sound ceases, in the timed mode. BR1, U5, and associated components form a power supply. Ql drives opto coupler U4 and triggers triac TRl. -If desired, four silicon diode rectifiers connected as a bridge can be substituted for BR1. Just make certain the diodes are rated at least 50V, 1A.

Low-cost semiconductor diodes such as 1N914, 1N4148 and 1N400X can be used as temperature sensors in applications where high accuracy is not required. They can be mounted on transistors, power diodes, transformers, heat sinks, rechargeable batteries, crystals, PCB, etc to monitor their temperature.

It is highly desirable to use temperature sensors with linear temperature characteristics and the mentioned diodes are best suited for that. To use them as temperature sensors, these diodes first need to be sorted according to their temperature coefficient. (Please refer ‘Signal Diode-Based Fire Alarm’ schema idea published in February 2013 issue to understand how these diodes can be used as temperature sensors.) This schema can help quickly sort different diodes based on their temperature coefficient.

The schema diagram of the device for selection of temperature-sensing diodes is shown in Fig. 1. The schema is built around step-down transformer X1, voltage regulator 7818 (IC1), voltage regulator 7809 (IC2) and three diodes 1N4001 (D1 through D3). The mains supply is stepped down to 21V, 250mA using transformer X1. Diode D2 is sufficient to rectify it since the required output current is typically below 20mA. The linear regulator IC1 provides the 18V power supply for the diodes (connected at CON1 through CON12) to be tested. The linear regulator IC2 provides the 9V power supply for the digital voltmeter (DVM) used for measuring the voltage drop across diodes.

Utilising this device, it is possible to test the diodes at around 0.1mA of forward current. The current for their PN junctions is provided through individual resistors R1 through R12. The value of a resistor is much higher that the resistance of the tested diode’s junctions, so changing the diodes will not change the forward current significantly.

 

The number of the connectors for the test diodes can be increased or decreased. The device does not need any adjustment or calibration to operate properly. To calculate the temperature co-efficient (TKU) of each diode and to sort the diodes accordingly, we need to measure the voltage drop across the diodes under test.

To sort the diodes, ensure that all of them are connected in the schema and the voltage drop (say U1) across each diode is measured one by one at the same temperature, say 25°C. The voltages can be read at TP3 through TP14 with respect to TP0 using the DVM as shown in Fig. 1. Now change the temperature to, say, 40°C, and take the measurements (say U2) again. We can use an electrical equipment, such as a heater, to produce the second temperature. So now the temperature coefficient of the PN junction for a diode will be:

The voltage drop change of the PN junction due to temperature change is linear, so we should take measurements at only two temperatures for each diode. The test temperatures can be the same for all the diodes or different. Most of the diodes can be used in the temperature range of -25°C to +150°C without any problem. The temperature coefficient of most of the PN junctions is in the range of -1.3mV/°C to -3mV/°C, so we can use these diodes as sensors.

An actual-size, single-side PCB for the device is shown in Fig. 2 and its component layout in Fig. 3. After assembling the schema on PCB, enclose it in a suitable plastic case.

To test the schema for proper functioning, verify correct power supply for the diodes and DVM at TP1 and TP2 with respect to TP0. Voltage drop across each diode can be verified at TP3 through TP14. 

Sourced By: EFY : Author: Petre Tzv. Petrov

This is the Simple Universal Laboratory Power Supply Circuit Diagram. The value of the design lies in the use of IC1, an LM317HVK adjustable s.eries-pass voltage regulator, for broad-range performance remainder supplies voltage-setting and current-limiting functions. 

The input to ICI-comes from the output of BR1, which is filtered by CI and C2 to about +60 Vdc, and the input for current-sense comparator IC2 comes from BR2, which also acts as a negative bias supply for regulation down to ground.

Simple Universal Laboratory Power Supply Circuit Diagram

This is a Simple Variable Dc Supply Step Circuit Diagram. Intended as a replacement for generally poorly regulated `wall-type` ac/dc adapters, this Simple Variable Dc Supply Step Circuit Diagram offers superior performance to simple, unregulated adapters. 

Voltages of 3, 6, 9, and 12 V are available. The DPDT switch serves as a polarity-reversal switch. R2 through R6 can be replaced with a 2.5-kfl pot for a variable voltage of 1 to 12 V. R7 through RIO can be replaced by a fixed resistor of about 1 kfi if the LED1 brightness variation with output voltage is not a problem.