LED strobe light with adjustable delay and duration. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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LED strobe light with adjustable delay and duration. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Ignition

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The device contains a MAIN CLOCK clock input for supplying a clock signal and an ultra-bright white LED output. The delay and duration of the LED glow are regulated by potentiometers P1 and P2. The circuit uses a universal green LED 1 to indicate the presence of an input signal, although this LED is useless when the stroboscope is operating at high frequencies.

Figure 1 shows a diagram of an LED stroboscope.

(click to enlarge)

A pulse signal with an amplitude of 5 V and a duration of approximately 30 μs is supplied to the input of the stroboscope from the vehicle's fuel pump. In this case, the potentiometer P1 regulates the delay time of the LED flashes in the range from 40 μs to 2 ms, and the potentiometer P2 regulates the duration of the glow (or flash) of the LED from 15 μs to 15 ms.

Diode D1 and capacitor C1 form a forming circuit. The discharge rate of the capacitor C1 is regulated by setting the potentiometer P1. The inverting Schmitt trigger IC 1A monitors the voltage level on the capacitor C1. As soon as the voltage reaches the low threshold of the 1C 1A trigger, a high level appears at its output, which is transmitted to the clock input of the D-flip-flop IC2. The Q output is set high. The Darlington pair of transistors Q1 and Q2 opens, current flowing through the bright white LED causes it to glow.

At this time, the capacitor C2 is charging, the charge rate is adjusted by the potentiometer P2. When the voltage on the capacitor reaches the upper threshold of the inverting Schmitt trigger IC1 B, the D-trigger IC1 will be reset through the 1C 2C trigger and its output Q will go high. The transistor pair closes and the white LED goes out. The circuit is now ready for another cycle.

Diode D2 provides a complete discharge of the capacitor C2.

Figure 2 shows process diagrams. 5 V clock input at 650 Hz. The upper curve of the graph shows the voltage on the white LED, the delay is about 250 µs (at P1 -10%) and the duration of the glow is approximately 600 µs (at P2 - 75%). The bottom trace shows the voltage at the Q output of D-flip-flop IC2.

(click to enlarge)

Fig. 3 shows diagrams with a different delay time for the same duration of the white LED (Fig. 2). The new fuel spray period overlaps the next fuel burst. Depending on the injector nozzle, one can observe the end of one calibrated flash of the fuel mixture and the beginning of another.

(click to enlarge)

The stroboscope is equipped with a switch to instantly increase the intensity (with resistance R3, the current through the LED is approximately 40 mA). When the BOOST button is pressed, a current of approximately 2 mA flows through the Darlington pair of 2222N400 transistors, i.e. Continued use of the switch may cause the white LED to fail.

Time intervals can be calculated using the formula: T = 0,7 x R x C, where T is the time in seconds, R is the resistance in ohms and C is the capacitance in farads.

Author: M.Page

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