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Old 01-21-2004, 01:55 PM   #11
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Someone can correct me if I'm wrong, but for dimming I'd attempt to use a pot (potentiameter) to control the voltage. This may have the desired voltage.

As far as the timer goes, I've only found plans to create a timer to run relays. But the problem is that it's timer based and not clock based. Therefore events only happen at intervals that you specify, not times. That means that if you want the lights to go on at noon and off at midnight, a 12 hour time, then that must be based on the current time. If you start the timer at 8am, then you would set the light to go on at 4 and off at 16.

Then again as a computer science and ME I'm now thinking that I should just write an application to control a bunch of relays based on signals sent from my serial port. Then everything could be based on the system clock in the computer.

That should shed a little bit of light on the topic for you.

Jim
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Old 01-23-2004, 12:20 AM   #12
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Hey Yaksplat - how are things. Wanted to add a little note to your advice above. Yep Potentiometers are good choice for dimming some things that are voltage sensitive however, LED's are really transistors that go to saturation at a particular foward volatage and then remain in that state (i.e. giving off photons) until they reach a max voltage at wich point the diode substrates become permantly biased (i.e. the thing gets burnt out).

Bottom line is that they sort of operate in a window of voltage and the amount of light they generate in the window is only midly different. So then the question - how do you dim an LED or group of LED's. The trick is to use a 555 timer chip as an Astable pulse generator. The frequency of the Pulses should be fixed and high like 5-10 Khz. However, the duty cycle of the pulses should be variable (the duty cycle is the relative on/off time ratio). For example, adjustable for 10% of the frequency the pulse is on and for 90% it is off adjust up to 90% of time the pulse is on and 10% it is off. The eye can not recognize that the LED's are being tunred an and off because the frequency is too high but the eye can detect the differnce in the ratio of how long the lamp is on or off.

I recommend the Forest M. Mims III hobby books available from radio shack. There is one specifically for the 555 timer and I believe it has a simple circuit to do this.

tom
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Old 01-25-2004, 10:35 PM   #13
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being the lazy person i am, i put a photo transistor in my circuit. so when the regular, timered light goes out, the moon light comes on, just like the night light in the bathroom.
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Old 01-28-2004, 04:03 PM   #14
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Hey guys, sorry about being a little late to the post..

I just finished up an associate degree, in EE about 1.5 yrs ago, and currently working on ba in computer science. If anyone needs any advice, suggestions, circuit diagrams, or explanations on components don't hesitate to ask, my email address is ijedi@hotmail.com or you can get a hold of my on aim or icq.

mad your right on the money, your explanations are perfect. Radio shack in my opinion is heavily overpriced, and a great alternative for circuit diagrams is to use google. i found this 555timer diagram back when i was getting my degree, it needs to be specially tuned for it's job, but it's pretty simple to do. http://www.mitedu.freeserve.co.uk/Ci...ng/555mono.htm

lastly though, 555timers from my experiences are unstable and unreliable. you wouldn't believe how many bad chips i have come across during my electronics degree and the few that did work, would either run great for a few hours, or they would generate very sporadic, crazy results. but on the light side, the chip is dirt cheap, and easy to wire. if you're going to use one, just make sure you triple check your wiring job before power is applied.

if anyone needs any help, just let me know!
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Old 01-28-2004, 04:59 PM   #15
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Hey Jprox,

Welcome - great to have an EE. I started in EE and about 3/4 of the way through my B.S. shifted to Comp Sci. But that was back in the early 80's. Went on to get a masters in Comp Sci as well.

It's been a little rough holding down the electronics-question fort, here at the Aquarium advice Alamo so I'm glad you joined.

Funny you have had bad experiences with the 555, it is a very standard chip and used all over the place. I've found it to be pretty reliable. Although I will agree that it is not very tolerant of operating, even for a fraction of a second, beyond its paramters. I.e. they burn out pretty easy so there are a lot of oops! if your not careful.

Tom
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Old 01-28-2004, 05:18 PM   #16
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well when they work, they rock. Most of the chips were provided by the college i attended, which could explain their behavior.. however about 1/2 through the program, a bunch of classmates and myself ordered about 25-30 7555 chips from digikey, and after they were divided up, 4 of the 6 i got were dead on arrival, the same was true for another classmate. the rest i played with were pretty much alright, expect for 1 or 2 that acted funny, having the timing systems distorted, or just popping the minute power was applied, which lead to my post about them. of course some of the problems could be contributed to operator error, but after you get to 4-5 dead chips you start looking for another reason you know? and after the digikey experience, i just started avoiding the 555 whenever i could.

lastly, it might be easier (and a little more costly) just to get a regular lighting timer from wal mart, and tear it apart and use that as the timer but add a step down transformer on the output to meet certain needs. i agree it's not very adventurous, but it will work quickly with minimal circuit designing and there is alot less to go wrong.

tom, i'm glad to help when ever i can and it's nice knowing i am not the only one with an ee and computer science background.

bryan
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Old 01-28-2004, 10:06 PM   #17
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I got my BS in Mechanical Engineering two years ago and i'm finishing up my BS in computer science this semester. Either of you consider writing a program to monitor and control your aquarium? That's the next thing i'm going to do.....



Jim
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Old 01-28-2004, 11:03 PM   #18
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Jim, i have thought about it, i really have. it would be awesome to have a computer monitor temp, lighting, chems ect then activate heaters/chillers start up the dosing systems or turn the lights on and off. I have like 3 486's laying around i would love to put to use. but that's a long away for me, i have a bunch of projects i need to finish before i can even think of trying this. [side note: Jim if you need anything computer related let me know i have bunch of old computer stuff i wouldn't mind parting with.] my stand just needs a finish and doors, i still have to design and build a sump/fuge system. finalize my filter selection (i have a bunch of stuff sitting in a box collecting dust, so i am trying to figure out which would be good to take out of retirement.) a boat load of cleaning to do on everything tank related and the list just goes on and on and on.

when i finally get around to it, i will be more than happy to post whatever i develop. hell who knows maybe we comp science majors can go into business selling software to control tank setups.. but isn't that somehow giving into laziness ?

bryan
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