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Controling light using parallel port

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clifweb

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Today at school when we were doing C# programming the teachers showed us a circuit that from the computer could control 8 LEDs on and of. I wish to make the same project but instead of lighting 8 LEDs I wish to light 6 bulbs 75W each. I know that the power need to be taken from the main but the signal Will be taken from the computer. Can some one tell me how to do it. programing is not an issue.

2nd
Is it possible from the same circuit dim the light separately.

Thanks very much.
 
Use opto-couplers switching TRIAC's - dimming is MUCH more complicated though.

You can also buy solid state relays, which are esentially the same thing.
 
There are a lot of those triacs/solid state relays that have built in zero cross detectors that makeing dimming applications a little easier to implement.
 
Sceadwian said:
There are a lot of those triacs/solid state relays that have built in zero cross detectors that makeing dimming applications a little easier to implement.

Sorry, but that's COMPLETELY wrong - a solid state relay with built-in zero-crossing makes it impossible to dim! - to dim you need to change the trigger point, and you've no control over it with built-in zero-crossing.
 
Could if it is imposible to dim each light by it self could I make a master dimmer that dims the enitre 6 75W light bulbs. But if i culd a part of that dim each bulb separetly it will be greate. since from the program I can create a script to dim themm all together
 
It's not impossible to dim the lights (unless you use a zero-crossing solid state relay), but it's a great deal more complicated - simply switching them with a PC is trivial, dimming isn't.
 
Can you tell me what is the most difficult if it is the programing or the circuit. Can some give me what i need to use and a good schemtic. for this job. I need only 6 lights and have the ability to dim them.
 
clifweb said:
Can you tell me what is the most difficult if it is the programing or the circuit. Can some give me what i need to use and a good schemtic. for this job. I need only 6 lights and have the ability to dim them.

To dim them, I would suggest you need a PIC on each channel, with the PIC programmed to do the dimming - the PC them just has to send a digital value to each PIC, probably via serial.

To dim a light you first need to generate zero-crossing pulses, then create an accurate, repeatable, time delay between the pulse and triggering the TRIAC - the longer the delay the dimmer the light (but not too long, or you hit the next half cycle).

For a good example of how you might do this in an analogue fashion, have a look at **broken link removed**.
 
Why do you need to change the trigger point to dim? The only thing a zero crossing triac would limit you to is dropping half cycles. Basically PWM'ing the bulb at 120hz. You likley wouldn't be able to get full off to bright dimming as flicker would probably show up more the dimmer you go bellow about 50%. Incandescant bulbs act naturally to filter out the pulses to a certain extent, after all people don't realize their bulbs actually flicker at 120 hertz because it takes a short period of time for the bulb to cool and stop producing light after the current stops.
 
If you drop half cycles you WILL see it flicker, you must use phase shift control to dim a lamp - what you're talking about is called 'burst fire' control, and is only suitable for heaters.

A microwave oven uses burst fire control, so how would you like your light to be dimmed by being ON for 5 seconds then OFF for 5 seconds - perhaps you might notice a 'flicker'?. Your pizza doesn't though!.
 
I fund this site **broken link removed** those this allow me to to switch on and dim the 6 lights that I have.
 
Nigel, are you sure it's going to be noticed? Light bulbs run at 120hz already, no one even thinks that a standard incandescent bulb flickers. I can't test it though. I don't think I have any diodes floating around I can send through a desk lamp to find out if a person would be able to visually notice flicker in it. Anyone wanna try it? I'd bet you can get to 50% dimming using half phase drops without noticeable flicker, unless you were right up against a hard shadow of the bulb. I have seen circuits based on CDS cells that can detect the flicker produced by a light bulb, but I'd be curious what amount of dimming (number of dropped cycles) would be required to notice it with the human eye.
I can easily notice the flicker on my peripheral vision of my monitor when it's sest to 60hz. But I have never noticed any flicker on light bulbs at 120hz, and I have better vision than most. Depends on the 'modulation' depth that the dropped cycles creates in the light output. There is a BIG difference between 60 dropped cycles in seriers with 60 full cycles as opposed to 1 out of ever 2 cycles being dropped.
 
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Having just OFF. Half Power, and Full Power is hardly 'dimming' is it! :D

But the flicker is likely to be easily visible, just stick a rectifier in series with a light bulb and see if you can see it or not? - quality of vision isn't a disadvantage, some people may not notice, but many will.
 
Gotta root through my junk bins and see if I can have any power diodes. Now I'm just curious =)
 
is this for a school project or a commercial application? if it's for your job, avoid the urge to DIY and go with prefab / off the shelf.

get some low voltage lamp dimmers (commonly used in commercial lighting setups) ... you feed it 0 - 10 vdc, and you get 0 - 100 % brightness on the lamp. you could use your parallel port here, each pin generates a pwm pulsetrain, which is smoothed into an analog voltage by an RC circuit

or use something like an X10 lamp dimmer, they only have 16 'steps' but it may be enough?
 
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