Police lightbar

Dr.killjoy

Joined Apr 28, 2013
1,196
I am very grateful for your reply but I am a complete novice. I really don't know where those holes are. There's nothing connected to hole 30. In the picture the breadboard is inverted.

Could you point this out for me? I'm sorry for being so stupid.

Thanks a lot.

Jess
Also you need to learn how to clean up your breadboard to help you find faults... The zener diodes are not connected to the 555 timer like in the schematic and also need to connect to pin 14 on the clock chip instead of pin 15..
 

MrChips

Joined Oct 2, 2009
30,712
You can build a simple logic tester circuit on your breadboard using an NPN transistor, an LED and two resistors.

I am not able to post new diagrams on AAC so I will use one of my album pictures to explain.



For your application, omit R1 and D1.
Replace the 9V battery with your power source.

For testing your 555 timer, connect the "Points" input to pin 3 of the 555 IC.
The LED should flash at the frequency determined by your 555 circuit.
 

radiohead

Joined May 28, 2009
514
Here's a possible solution to your project. It uses only a few components but it works fine with one 555 and a couple transistors.

The capacitor affects the frequency (blink rate). As you know, the NPN conducts with a positive bias and does not conduct without a bias voltage. The PNP conducts with no bias on the base and will not conduct with a bias voltage.

As the sine/square wave is fed from pin 3 to the transistors, they will alternately turn on. However it will not blink three times on one LED then switch over to the other.

It should fit the bill for most hobby projects requiring only a few parts.
 

Attachments

Thread Starter

archangeljess

Joined Dec 27, 2013
34
Also you need to learn how to clean up your breadboard to help you find faults... The zener diodes are not connected to the 555 timer like in the schematic and also need to connect to pin 14 on the clock chip instead of pin 15..
I agree I need to work on cleaning my board. I also the connected diodes to the 14th pin but it is still not working.

@radiohead:
I guess I am going over my head on this one. I admit I skipped a lot trying to build this circuit without significant prior knowledge. I will try working on your suggestion.

@MrChips:
Just to be sure I understand you correctly. I will connect the positive of the "points" in the circuit you provided to the 3rd pin on 555 and the negative to the ground on my breadboard. Did I get it right?

@sirch2:
I will buy another 555 IC later today just in case i busted my 555 IC in the circuit.

@tubeguy:
I also did your suggestion to remove the ground on the unused pin but to no avail. its still not flashing. I will rewire this thing later today so it will be more clearer to view and will upload a picture of what i did for you to look at.

Thanks everyone for helping.

Jess
 

R!f@@

Joined Apr 2, 2009
9,918
U need to make sure tht the 555 is working.

Remove the connection between pin3 of 555 to 4017 and to the diodes.
This will isolate the 555 and 4017.
Next connect an LED in series with 220R to pin 3 of 555 to GND. LED anode should go to pin3 of 555. When U power up the LED should flash rapidly if the 555 is working
 

Thread Starter

archangeljess

Joined Dec 27, 2013
34
U need to make sure tht the 555 is working.

Remove the connection between pin3 of 555 to 4017 and to the diodes.
This will isolate the 555 and 4017.
Next connect an LED in series with 220R to pin 3 of 555 to GND. LED anode should go to pin3 of 555. When U power up the LED should flash rapidly if the 555 is working
I guess I have to replace my 555 timer. When I do your suggestion the LED doesn't light up.
 

Thread Starter

archangeljess

Joined Dec 27, 2013
34
Just one quick question though. Most of the other schematic that I saw for flashing LED uses 9volt battery. Would it be possible to use a 12volt power supply on a schematic that uses 9volt battery? If so, how will I do that?

Thanks a lot.

Jess
 

Wendy

Joined Mar 24, 2008
23,415
12 V is fine, though you will want to adjust the resistors on the LEDs to a higher value to compensate. Both the 555 and 4017 are rated for either voltage.
 

Thread Starter

archangeljess

Joined Dec 27, 2013
34
I just found a new schematic for a police flashing light. They seemed to be identical. What do I need to do to make the power supply 12 volts? Here's the schematic:

 

MrChips

Joined Oct 2, 2009
30,712
Do nothing. If the LEDs are too bright you can increase the values of R7-R10 to 1kΩ.

Note that the lower power rail is mislabeled as -9V. This should be 0V, GND or COM.
 

tubeguy

Joined Nov 3, 2012
1,157
I just found a new schematic for a police flashing light. They seemed to be identical. What do I need to do to make the power supply 12 volts? Here's the schematic:

I would change R3, R4 and R7 thru R10 from 470 ohm to 1000 ohms.
BTW: Not identical :rolleyes:
 
Last edited:

Thread Starter

archangeljess

Joined Dec 27, 2013
34
I went to my local electronics store the other day but I cannot get a 1N4148 diode. They say that its not in their stocks yet. The new schematic that I posted uses 6 of those diodes. Is there another diode I could use as a replacement to 1N4148?

Thanks.

Jess
 

MrChips

Joined Oct 2, 2009
30,712
1N914

These are not replacements but will work and are readily available:
1N4001
1N4002
1N4003
1N4004
1N4005
1N4006
1N4007
 

Thread Starter

archangeljess

Joined Dec 27, 2013
34
I want to thank everyone who posted their ideas and suggestions on my little problem. I finally figured out how to make this circuit work. I just ran into some problem with the diodes that my local electronics store sold me. I think they sold me the wrong one. Good thing I had 2 1n4148 diodes when I tested my circuit only the red LED are flashing slowly. I think I have to find another store which sells 4148.

I have another question though. How will I add another 2 red and 2 blue LEDs into the circuit. By the way I followed the last schematic that I posted not the first one labeled police lights 2.

Thanks everyone.

Jess
 

R!f@@

Joined Apr 2, 2009
9,918
The diodes will work. They all drop around 0.7V.
Difference is 1N4148 handles around 75mA while the 1N4000 series can handle 1 amps
 

Thread Starter

archangeljess

Joined Dec 27, 2013
34
The diodes will work. They all drop around 0.7V.
Difference is 1N4148 handles around 75mA while the 1N4000 series can handle 1 amps
Thanks for the reply R!f@@.

Am I right to assume that if I use the 1N4000 series diodes I can increase the number of LEDs I can connect to it? Pardon me for my ignorance.

Thanks

Jess
 

Thread Starter

archangeljess

Joined Dec 27, 2013
34
No. In the circuit you have shown diodes D1-D6 are used to create a logic OR function.
What do you mean MrChips? What can I do to increase the number of LEDs?

If I want to have another set of LEDs (white, I guess) that blinks in another sequence from the red and blue LEDs much like a turn signal on hazard, what will I need to modify? Or I shall need another circuit for that?

Thanks

Jess
 
Top