Bike turning signals

[ImpulsE041993]

Can someone explain how this circuit works?or what is the flow of ths circuit?
i really need it..plzzzz...
https://www.555-timer-circuits.com/bike-turning-signal.html

and what is the purpose of the 2 diodes(1N4148) and the connection of the five transistor?

 

[dougy83]

the diode to the right just provides a 0.7V drop (affects the fade in or 'sequencing' rate of the leds). The other diode is to discharge the capacitor quickly so the LEDs fade on slowly (cap is charged slowly through resistor) and they all turn off quickly (due to the fast discharge of the cap).

 

[ImpulsE041993]

why is that the lighting of LED starts from the right to the left?thus the transistor affects the direction?

 

[dougy83]

the voltage on the capacitor rises slowly when the output of the 555 is high; as this voltage passes the turn on voltage for the rightmost transitor (1.4V - 0.7V for Vbe, and 0.7V for the diode), the rightmost LED turns on. As the voltage increases further, the other transistors conduct in turn and light the connected LEDs - each when the capacitor voltage is 0.7V more than the previous transistor turn on (due to the transistors being stacked)

 

[ImpulsE041993]

how did you get the 1.4V?is that a fixed voltage drop?

 

[dougy83]

0.7V is a rough figure for the voltage drop of a silicon PN junction (it can vary). There is 1 PN junction between the rightmost transistor's base and emitter and another in the rightmost diode; they are in series so the voltage drop is the sum of the two

 

[ImpulsE041993]

tnx for helping me.

 

[ImpulsE041993]

can i ask?y not the turn ON of the LED's starts from Q1?IS it bcoz of the resistor?

What do u call that arrangement of trAnsistors?

 

[ImpulsE041993]

i really need it plz..

 

[audioguru]

The base-emitter junctions of the transistors are in series. Each junction has a voltage drop of 0.7V.
Then Q5 turns on when its base is 1.4V, Q4 turns on when its base is 2.1V, Q3 turns in when its base is 2.8V, Q4 turns on when its base is +3.5V and you can simply calculate the voltage at the base of Q5 that turns it on.

 

[dougy83]

Attached picture shows the voltage drops of the transistors required for them to turn on. Try working out the voltage at the base of each transistor required for it to turn on (they're series-connected, so you add them)

The voltage on the capacitor is a ramp from 0V to ~10V, you should be able to see how this will turn on each transistor as its voltage exceeds the turn on voltage of each node in the transistor chain.

 

[colin55]

Where did you get that circuit? Someone has taken my circuit and called it their own.

 

[dougy83]

I thought I recognised it! I believe the same cascaded transistor setup is used in the old Dick Smith VU meter project

 

[ImpulsE041993]

tnx..

 

[jeeski28]

it really helped me a lot...tnx...

 

[jeeski28]

can you give me a block diagram of that circuit(bike turning signal circuit)?
i really need it...please...i need help....

 

[Electroenthusiast]

Jeeski... 555 timer generates pulses and LEDs are used to glow lights. Transistor to provide the driving current. So i think you can make a block diagram out of it.

 

[jeeski28]

thnx...

 

[Electroenthusiast]

interesting thing about my previous post was i was speaking about 555 timer and it was also my post number 555.

How many times will this happen?

 

[jeeski28]

another thing...is the theory of operation of this circuit the same as its application?