Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

LED doesn't turn Off

Status
Not open for further replies.

Blisk

Junior Member level 1
Joined
Jan 3, 2015
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
165
I have this circuit and when I start NE555 led goes RED and that it doesn't change to GREEN, relay turns on and off but LED doesn't change, I think it is problem because difference on transistor B/E is about 0.84V.
Any Idea how to solve this problem??

2017-01-05 08_44_42-1 Schematic.sch - EAGLE 7.jpg
 

The problem is that both leds will go on /off simultainously because they are connected to the same output.
There is an easier way if you want to create a flip /flop--> led alternating color red / green. , see schematic... a assumed that it is a 2 color led in one....not two individual leds, right?
Also I would put a diode over the relais to protect your NE555 from inductive spikes
IMG_0714.JPG

- - - Updated - - -

If you use two leds, there are better options
FlashingLights.gif

tim45.gif
 

Thank you, a third circuit is what i had before but now I have 2 color 3 pin common cathode led.
Problem is I already have PCB board with my circuit above, how to solve that?
Both LEDs are on the same source but one goes ON when output of NE555 is high and other when it is low over PNP transistor. Yes that is LED with 2 color and 3 pin common chatode.
 
Last edited:

Try the first schematic I posted ( the one I did on a piece of paper with pen)
 
  • Like
Reactions: Blisk

    Blisk

    Points: 2
    Helpful Answer Positive Rating
I will, thanks.
For now I solve this by putting transistor in pcb wrong way, I changed E and C and put in larger resistor on base like 68Kohm
Red still lit when green is on but verry little.
 

The circuit is not clear to me. It is seen you have used the 555 in astable multivibrator mode. What function have you done by reset pin? How you utilise "ON/OFF" associated with reset pin? Also confirm whether JP2 is contacts of relay or something else. Have you driven the relay directly by 555?
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top