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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

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 schema diagram shows, in the present schema, 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.

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 schema, 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.

The article describes a very simple homemade emergency light schema that can be used during power failures and outdoors where any other source of power might be unavailable. The schema uses LEDs instead of incandescent lamp, thus making the unit very power efficient and brighter with its light output. Moreover, the schema employs a very innovative concept especially devised by me which further enhances the economical feature of the unit.

We know that LEDs require a certain fixed forward voltage drop to become illuminated and it is at this rating when the LED is at it’s best, that is voltages which is around its forward voltage drop facilitates the device to operate in the most efficient way.

As this voltage is increased, the LED starts drawing more current, rather dissipating extra current by getting heated up itself and also through the resistor which also gets heated up in the process of limiting the extra current.

If we could maintain a voltage around an LED near to its rated forward voltage, we could use it more efficiently. That’s exactly what I have tried to fix in the schema.

Since the battery used here is a 6 volt battery, means this source is a bit higher than the forward voltage of the LEDs used here, which amounts to 3.5 volts. The extra 2.5 volts rise can cause considerable dissipation and loss of power through heat generation.

Therefore I employed a few diodes in series with the supply and made sure that initially when the battery is fully charged; three diodes are effectively switched so as to drop the excess 2.5 volts across the white LEDs (because each diode drop 0.6 volts across itself).

 Now as the voltage of the battery drops, the diodes series are reduced to two and subsequently to one making sure only the desired amount of voltage reaches the LED bank.

In this way the proposed emergency lamp schema is made highly efficient with its current consumption, and it provides backup for a much longer period of time than what it would do with ordinary connections.

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.

Most PN-junction diodes can be used as photodiodes. While not optimized for this application, they do work. When the diode is reverse biased, it will produce a small photovoltaic output as the light level is increased. LEDs are particularly suited for this task because their housings are transparent.

You can construct a simple schema that will assess the condition of ambient lighting and, because many LEDs’ packages are tinted to enhance their emitted color, may even yield a reasonable evaluation of the detected color. The results are not as effective as those obtained using a high-quality optical filter, which typically has narrow bandpass characteristics, but they can be quite acceptable. Though the design described here does not produce the accuracy of designs with laboratory-grade photodetectors and transimpedance amplifiers, it can be quickly assembled and will produce usable results at a low cost.

Three LEDs are used; experimentation will indicate which device has the best sensitivity to which color (Figure 1). The ambient light falling on the LEDs causes some current flow—typically in the range of 10 to 100 nA—through each LED, depending on the applied illumination level. This current flows through the base of a transistor, Q1, and is amplified. Q1’s collector current then splits between potentiometer R4, which acts as a first-stage gain calibration, and the base of Q2.

Photo Meter Assesses Ambient Light Schematic

Q2 provides further amplification and drives the left side of a bridge schema (D1A and D1B). Note that R2/D1 and R3/D2 form a balanced bridge. Q2’s collector current provides a slight imbalance to the bridge. The meter, M, measures this imbalance. R5 adjusts the sensitivity of the meter. Set R4 and R5 such that the meter has an appropriate deflection. R4 is useful for selecting the quiescent point; R5 is useful for adjusting the sensitivity.

Before building the schema, check whether the LEDs can be used as photo sensors. To determine whether a given LED is a good photodiode, check the voltage across the LED using a common digital multimeter set to its most sensitive range—typically 200 mV. Typical output voltage should be approximately 0.3 to 1 mV with typical office illumination. 

This is Simple Electronic Light Sequencer Circuit Diagram. The light sequencer uses two ICs and 10 SCRs to create.an ac sequencer. The first 10, a 555 timer, is used to provide clock pulses for 102. The 10 is configured as an astable multivibrator, and its output is on pin 3. 

Capacitors CI and 04, along with resistor R2 and potentiometer PI, control the frequency of the pulses. IC2 is a 4017 Johnson counter, which shifts a high-signal level to each one of its 10 output pins in sequence. Each output pin is resistively coupled to the gate lead an an SCR. When the respective output pin on the 4017 is high and the positive half of the ac cycle is on the anode lead of the SCR, it turns on.

The lamp that is connected to its anode lights. Power is brought into the PC board by the line cord, then the schema is fuse-protected. Diode LD1 changes the ac to pulsating, which is smoothed by C2 and C3. R23 limits the current, and zener diode D2 limits the dc voltage to 6 Vdc.