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Arrowboard with analog circut?

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Andy1845c

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Hello, Let me start off by saying that I am new here, and new to the electronics world. (bet you have never heard that before on here, lol)

I want to make an arrow board, like you see on the back of a street dept. truck, or a police car. Basically a bunch of amber LEDS wired in blocks that will light up one at a time from left to right, or right to left, and then stay lit until the last one lights, then reset and start over. From reading on here for the past few months, I'm guessing a micro controller would be ideal?, but at this point in time that is way over my head. Has anyone seen a layout for anything simalier to this? Does it sound impossibly complicated for a novice?

I want to put this on the back of a roadgrader, but mostly want to make it for the learning. Any input would be awsome!

Andy
 
For this simple project, you don't need a micro. Use a 555 timer in astable mode (the datasheet will show how) as clock and a shift register to move the lit leds. With a 12 volt supply, you could have up to six LEDs in series. 4000 series CMOS doesn't have much current drive, so you will need a transistor switch on each shift register output. Do some research and come back with more questions.
 
I saw something like that using a 3914 bar/dot driver chip. Just need a ramp generator, and 10 drive transistors. Oh, the amber is really a cluster of red and green Leds. I've seen these at several surplus sites, but a little pricey, but claim to be visiable day or night.
 
Thanks for the replys everyone!

Russlk - Thanks for pointing me in a direction to research. Thats exactly what I was looking for. I just finished a good hour of reading about the 555. lol My brain is fried for the night, but it is all starting to make sense. :D

With a shift register, can I hold LEDS on, until all are lit? Say if I have 8 LEDS, can I make it so 1 comes on and stays lit while 2 comes on, then 1 and 2 are still on while 3 comes on, all the way until 8 lights, then have it reset and start over? Or will it just make them march 1 at a time?

Thanks agian for the help!!!
Andy
 
"With a shift register, can I hold LEDS on, until all are lit? Say if I have 8 LEDS, can I make it so 1 comes on and stays lit while 2 comes on, then 1 and 2 are still on while 3 comes on, all the way until 8 lights, then have it reset and start over? Or will it just make them march 1 at a time?"

You can do it either way. I don't know if there is a 4000 series equivalant to the 74xx164, but that is what you want. To have them all on, tie the D input high; to have them march, D needs to be high only for the first clock pulse.
 
Hey guys,

I have been studying all I can about the 555 and just today had a chance to go buy a couple to play with. I tried setting one up astable to blink and LED, but it didn't work. The LED stays on steady. I have double checked my connections and they all seem correct. Unless I have the thing upside down or somthing. The one I have has a dot on it in one corner(on the the side that faces up when installled), and from looking at different diagrams, I figured that the dot must go in the top left corner and then the pins are numbered as if you were looking down on it, with pins down?

The only other two things I can think of are that I messed up my Freq. calculations and the thing is blinking so fast I cant tell.

Or more plasuable, I cooked it trying to solder its tiny little pins. Is there a way I can test it with a DMM? It didn't get all that hot, but I'm not sure how delecate they are either.

Also, I read the 555 sould have a diode to protect it. I don't know half as much about diodes as I would like to. I have a bunch of them in junk PCBs that I could un-solder and remove, but I don't know how to tell if they are the right types of if they would even work for this type of app. Does anyone know of a good website that explains how to use them? I know how they work and what they do, I am just not familiar with how many differnt ones and sizes there are and how to sort them.

I'm trying to get comfortable with the 555 timer and then move on to leaning how the shift register works.

Thanks in advance for more help.

Andy
 
R1 is 10k, R2 is 100K and C is 1uF, that should be 6.8 Hz, according to the chart on here http://www.kpsec.freeuk.com/555timer.htm

I think i might have fried my poor 1uF cap with the iorn:( upon close inspection, it had a small blister on it. I'm starting over. I'll post again if I get it flashing tonight;)

On a side note, to do the math manually for freq., and reffering to the above website, what does the value 2R2 mean? The rest makes sense, but I can't remember anything in algebra like that. I know R2 is the value of resistor 2, but the first 2 is confusing me.

Thanks

Andy
 
well, I just finished redoing it. and it still dosn't work. No i have no idea why. I don't know why somthing so simple is giving me so much trouble..... grrrrr
 
6.8 Hz is almost 7 flashes per second. Might be a little fast to notice. An average flashing type LED is 2 per second, pretty quick.

Try R1 = 68K, R2 = 27K, C1 = 22uF. It's .52 Hz @ 54% duty cycle, went with the closest standard values.
 
Hey!

I finally got it working lastnight!! A blinking green LED looks better then 4th of July Fireworks to me! :D Now my next question is, can someone point me toward a website where I can learn about shift registers? I did some searching on Yahoo, but I didn't find much. How many different types are out there? Where would be a good place to order a few? I checked radio shack and they don't have any here in town. :(

Andy
 
Is a decade counter the same as a shift register? mabey I am searching under the worng name....
 
Radio Shack is useless anymore. Check out Mouser or DigiKey (www.mouser.com, www.digikey.com) Digikey has a good search engine.
There are many shift registers, look up these data sheets:
74xx195, parallel in/parallel out, shift right
74xx194, parallel in/parallel out, bidirectional
74xx164, serial-in/parallel out, shift right
74xx165, parallel/serial in, serial out, shift right
74xx91, serial in/serial out, shift right
 
A counter and a shift register are entirely different things. Both are composed of flip-flops but the counter divides by 2 in each section and the shift register just slides the data along the sections.
 
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