Help me in calculating base resistance for transistor

Thread Starter

rahulb

Joined Jun 5, 2019
20
Hi,

I am making a circuit for a led chaser. the leds should glow one by one.

I am testing the circuit with one led for each transistor later I will add array of leds to each transistor.

I want the base resistor value to make the transistor turn on. Leds will have resistors to limit current to them.

Problem is : first led is glowing continuously, second one is not glowing and third one is glowing dim but continuously. they should glow and turn off one by one.

Voltage used is : 12v DC

ledlight.png

datasheet link : https://bit.ly/32yOfpg

thanks
 

Dodgydave

Joined Jun 22, 2012
8,465
Could be the clock speed too fast, put a led on the output of the 555 timer to see if it's working,.. Your circuit looks ok.
 

Picbuster

Joined Dec 2, 2013
979
Hi,

I am making a circuit for a led chaser. the leds should glow one by one.

I am testing the circuit with one led for each transistor later I will add array of leds to each transistor.

I want the base resistor value to make the transistor turn on. Leds will have resistors to limit current to them.

Problem is : first led is glowing continuously, second one is not glowing and third one is glowing dim but continuously. they should glow and turn off one by one.

Voltage used is : 12v DC

View attachment 189318

datasheet link : https://bit.ly/32yOfpg

thanks
Remove IC1 and pulse 4017N pin 14 using a button.
next step is to measure the 555 out when installed (speed).
Personally I prefer fets above transistors when switching things. ( low internal resistance and a voltage driven input)

Picbuster
 
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