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How do i go about building AC light scrolling Display

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kevilay

New Member
Hello, im an electronics engineering student. Recently i came across these lights that were given to me. Their for the signs outdoors on casinos. Its a 2.5 watt 120v ac light. Each light has about 20 little super bight leds on it. I would like to make a scrolling display out of them somehow. I have about 100 of them and might be able to get more. What would be my best way to go about building this. I have a little programmable PIC but it only has like 13 outputs on it. I have a digital trainer with a breadbord. the trainer is 15v and the pic is 5v output, both dc of course. Is there a way i can control the lights using an ac circuit but use my programmable pics 5v output to turn the lights on and off? Also what would have need to control a large scale (100 lights) version of this? Sorry for being kind of ignorant towards this topic, im very familar with DC but have done little to no ac work.

Thanks
Kevin
 

c36041254

Member
Hi Kevin,
All you need is just some multiplexers and relays, use multiplexers to get more outputs from PIC and use those outputs to drive relays and control AC with them to drive LEDs.

Have fun !
 

kevilay

New Member
thanks for your input, do you know off hand more specifically what relays or multiplexers to use, or where i can get my hands on a circuit thats somewhat similar to what im trying to do? Not sure if it matters but my pic is 16f84a with a 5v output. If its to much work dont worry about it just wondering if you know offhand.

thanks so much
kevin
 

c36041254

Member
just search for solid state relays for 120 V AC , program the PIC for whatever scrolling pattern you like and multiplex the output of PIC with multiplexer and feed its output to relays and you are don e, I'll be posting the possible ckt for it but you better try for your self first.
Good luck !
 

kevilay

New Member
just search for solid state relays for 120 V AC , program the PIC for whatever scrolling pattern you like and multiplex the output of PIC with multiplexer and feed its output to relays and you are don e, I'll be posting the possible ckt for it but you better try for your self first.
Good luck !
something like a 120 VAC, 3 Amp, DC Control Solid State Relay would work right? how do i hook it up. Just say i want to hook up 1 light directly from an output on my pic to a light?

Kevin
 

tcmtech

Banned
Most Helpful Member
At 2.5 watts each just run them directly off of triac opto couplers with a small snubber capacitor across the AC side. I have seen that done in many sign control boards that are specifically built for LED based bulbs.

The good triac optos have 250 - 600 volt and 100 - 300 MA capacity.
There are also ones like this that are more for what you are doing.
This one has a 600 volt and 1 amp peak rating. Plus it costs about a $1.
 

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kevilay

New Member
I was looking at the pdf file of a triac, so i need one of those for each light? How would i setup say 2 lights just running to 2 different pic outputs. Im not really sure how to hookup that chip.

Thanks for your help
kevin
 

kevilay

New Member
is anyone familiar with hooking up the opto couplers and can give me any advice, im not really sure how they work.

Thanks
Kevin
 

tcmtech

Banned
Most Helpful Member
The input uses a standard LED type diode so just make sure you are giving it at least its minimum rated current after factoring in the voltage drop across it.
The output can run small loads directly or can be used to trigger large Triacs for big loads too.
For direct load running just make sure your peak load amps are below the rated peak amps and use a snubber cap or MOV of some type across the AC side.
 

kevilay

New Member
The input uses a standard LED type diode so just make sure you are giving it at least its minimum rated current after factoring in the voltage drop across it.
The output can run small loads directly or can be used to trigger large Triacs for big loads too.
For direct load running just make sure your peak load amps are below the rated peak amps and use a snubber cap or MOV of some type across the AC side.
that definitly went right over my head, is there a simpler way to explain it? Cause i dont understand how to hook up the chip at all, ive never really created my own circuits, normally were just given diagrams and ive built stuff. I also have never done any ac stuff

Kevin
 

Sceadwian

Banned
kevilay, if you're an engineering student and you don't understand what tcmtech said I would strongly recommend rethinking your school plans. A basic electronic circuits 101 course should teach you what forward diode drop and how to calculate voltage drop across resistor the first DAY. The existance and possible uses for a triac should be a least mentioned within the first few weeks.
 

tcmtech

Banned
Most Helpful Member
If I did not know better I would almost guess he is going to the same EE course I went too my second time back at college! ;)
They honestly did not cover basic stuff like that either! :eek:

Your not from a certain college on the east side of my state are you? :confused::p
 

Sceadwian

Banned
That's is seriously beyond my comprehension how that could occur. I hope I didn't offend you kevilay. If your basics are that off I'd recommend visiting a site like All About Circuits : Free Electric Circuits Textbooks
and brushing up on your own time, it will provide you with a WORLD of insight into EE in general. I especially recommend learning how basic semi conductors work
 

kevilay

New Member
I'll definitly brush up on it, i know we did some of the basic courses but they were brief most of my school focuses on plc's and robots, im actually eet industiral automation. Im familar with the diodes and the voltage drops and stuff. But i dont know anything about ac. Normaly theirs like a .7V drop across a LED but how does it work cause the bulbs i got screw in just like a regular AC bulb socket. I would know how do hook the light up with a relay up to my pic, but ive never used one of those opto coupler chips before and am not familar with how to hook it up to one of those. Sorry for being kind of ignorant on the topic, and i really appreciate the help from you guys.

Kevin
 

tcmtech

Banned
Most Helpful Member
At least you admit to it. Thank you!

All you need to do is treat it like a very small relay. The input is a diode so it will only work in one direction. Assuming the Opto coupler diode has the common 1.2 volt drop across it and it had a minimum running current of 5 ma and you were powering it off of a 5 volt source
You would have 5 - 1.2 = 3.8 volts. You need at least 5 ma at the 3.8 volt drop so that means 3.8/.005 = 760 ohms.
being the IC I posted has a input current of 5 - 60 ma any resistor between 63 - 760 ohms would work.

The output side can be treated like a very small relay as well. just keep in mind that it has a 1 amp peak rating and a 100 MA continuous rating. and like any good relay designer you will need to put a snubber or voltage spike suppressor in parallel with the relay contacts.
For the very small current that a LED based light uses a .01 uf or probably even smaller will be sufficient. All it is doing is help knock down any voltage transients that may occur when the device switches off.
 

kevilay

New Member
At least you admit to it. Thank you!

All you need to do is treat it like a very small relay. The input is a diode so it will only work in one direction. Assuming the Opto coupler diode has the common 1.2 volt drop across it and it had a minimum running current of 5 ma and you were powering it off of a 5 volt source
You would have 5 - 1.2 = 3.8 volts. You need at least 5 ma at the 3.8 volt drop so that means 3.8/.005 = 760 ohms.
being the IC I posted has a input current of 5 - 60 ma any resistor between 63 - 760 ohms would work.

The output side can be treated like a very small relay as well. just keep in mind that it has a 1 amp peak rating and a 100 MA continuous rating. and like any good relay designer you will need to put a snubber or voltage spike suppressor in parallel with the relay contacts.
For the very small current that a LED based light uses a .01 uf or probably even smaller will be sufficient. All it is doing is help knock down any voltage transients that may occur when the device switches off.
ok i think im starting to understand, how do i know which pins go where on that little chip? any chance i could have ya pop open paint and draw a cheap schematic and you would be my best buddy ever.

Thanks
Kevin
 

tcmtech

Banned
Most Helpful Member
The chip pin layout is in the data sheet I posted earlier.

As far as being my best buddy, Well the last one just bounced a big check he wrote to me so the position may be opening up soon! :D
 
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