first off hello...im new around here....i joined the site because of the knowledge....alot...almost overwhelming...i was looking to build some police lights i came across this schematic drawn by Mr. Bill Marsden on this site...please forgive me for pasting the scheme in my post but due to the age of the original thread i was no longer to post...i have a question about the schematic..i need help figuring out some values...i will be running 9v...i would like to make each bank 10 lights instead of the 15..and i would like to also change one of the light banks to red...i was hoping perhaps maybe someone could help me figure the different values of components needed to complete the build....as always thanks...the kid

 

Heh, I've forgot even drawing that schematic. I might be able to do better 2nd time around. Is this for a model car (I hope)?

Where was the thread you got it?

An article I wrote that might have better information...

LEDs, 555s, Flashers, and Light Chasers

Bill's Index

What part of the country or world are you?

Drop both banks to 2 LEDs per chain. The red would need 220Ω, the blue would need 91Ω. One word of caution, a 9V battery will work, but it is a very poor choice. They quickly drop to 7V, for example. You could make 9V using AAA or AA batteries, which would last longer.

 

Bill, I see this circuit uses the 4017 as a sequencer to create an alternating double flash. I've used it in similar fashion to make a triple flash safety blinker with a single bank of LEDs. In my circuit, I don't have any of the diodes (CR1-CR4 & VR1, VR2) you have in your design. What's the purpose of them?

 

Did you short your ouputs together, or use resistors for isolation? They are basically diode OR gates.

This is a very old schematic for me and this site. I don't remember ever having drawn zeners in them, but that is my style of drawing, so I can't deny it. It is why I would like to know what thread it is from. There may be some context I don't remember here, or it could just be an early drawing.

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I remember it now. It was an automotive circuit, something that is not permitted now. It was for when the car's electrical system was running 13.7V, as opposed to the 12V battery voltage. It keeps the LED current constant.

 

thanks for your response Bill....i spent prolly close to 3 hours skimming thru your cookbook before i signed up last night...remarkable sir!..there was so much stuff in there i couldnt just stick to one reading one thing...ok..here is the link to the thread i was referring to..http://forum.allaboutcircuits.com/showthread.php?t=17499...the drawing is located on the last page...and yes...this is for a model car in the 1:18 scale...and i am located in the Mid-West of USA..thanks again for the response...

 

I enjoy LED circuits, so I tend to draw to order. Have you put any thought into what I said about the battery? When you know the battery is not stable there are things (like constant current sources) you can do to stabilize the current through the LEDs.

I've also come up with some neat schemes that can power up LEDs with very low voltages (and are really bright). I didn't invent them, but I have made them mine. I can power this circuit off of 3V for example.

Red LEDs are never as bright as blue. I'm not sure why this is so, but it is a problem. You may want to up the numbers of red LEDs, or throttle back the brightness of blue LEDs.

Another thread for something very similar was here...

http://forum.allaboutcircuits.com/showthread.php?t=37409&highlight=police

This is not the best way, but it works. The thread has a YouTube link that shows a prototype I built.

Like I said, will draw to demand. If you want a full list of other threads I've helped out with just ask.

The above drawing, if you print it with Windows Fax/Image View you will wind up with a very acceptable print.

We don't do vehicles anymore, but RC cars are OK.

 

Bill, regarding my peripheral question.

Did you short your ouputs together, or use resistors for isolation? They are basically diode OR gates.

The outputs of the 4017 went directly to inputs on a 4075 (3-input OR gate). I'd forgotten that when I asked you about the diodes. I guess I mostly wanted to know about the zeners.

 

Something I tell a lot of people, there are lots of ways to do something like this and similar projects, none of them wrong. Lately I lean towards using using MOSFETs, which have a lot of better characteristics than BJT (standard transistors). However, standard transistors are easier to get, so it is half of one, half of another. Mostly I try to make it easier for beginners.

 

FYI: One of the largest manufacturers of emergency vehicle lighting in the U.S. is Whelen Engineering. They have an online flash pattern demo: http://www.whelen.com/media/flash_patterns/index.htm.

 

thanks for your help bill...do you have a PayPal donate??...seriously...the help is appreciated...currently for my model cars i buy these pcbs which have flash patterns on them...i have included two pictures of the pcbs..here is the link for those photos..http://img835.imageshack.us/g/lightbar.jpg/...one of the front and the back..

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.i have been wanting an attempt to create my own...i bought some components from mouser last nite...i will post a parts list of what i bought...may be easier to help suggest something that way...again i thank you for your help

 

i ordered a couple icm 7555 and a couple cd4017..

 

The 4017 is a good little chip, great for these kinds of applications. So is the 555 or CMOS 555 (they should be considered separate chips).

The stuff I'm showing won't be that small. It could be, the parts are out there. That PCB you're looking at is a µC. If you are into writing code they really are the easiest way to make circuits like these. A µC is a small computer on a chip, which makes it very flexable and open ended. I don't do µC though.

Don't worry about money around here. This is what we do for fun.