time controlled rheostat

[Journer]

ok, so i am looking for something i guess would be considered a time controlled rheostat. Basically, all i want to do is hook something up to my snake's lamp so i can create a virtual sunrise. i know it works in theory becuase ive hooked a rheostat up to a lamp before...you slowly turn it and it is kind of like the sun in rising. so, now i just need some kind of device that does it automatically based on the time frame given.

anyone know wtf i'm talking about?

 

[bobdole369]

Yup, I understand.

Only need a moderate understanding of electronics to make it work. You'd need a 555, some transistors, some caps and resistors.

Other method could be a software driven PWM. Such a device exists here - http://www.zworld.com You want the RabbitFLEX board. You'll need to program it either in C or assembly and use the PWM output (which basically adjusts voltage output), to drive a transistor that will pass your light current.

Sorry I'm no EE, and I can't exactly whip out a schematic in 30 seconds, but at least you know its possible.

 

[ScottMac]

The easy thing might be an X10 module, computer interface and software (comes with the computer interface).

Check out www.smarthome.com or x10.com.

If you go to X10.com make sure your firewall, filters, nad pop-up blockers are all tuned up, their site is about a half-step under your average aggressive porn site. I hate it.

SmartHome.com has most of the home automation stuff and is generally a much better site.

Good Luck

Scott

 

[PsYcHoCoW]

That's a nice little project

if you want to do it yourself, you'll most likely end up using a device called a Triac to power the light (a Triac is like a transistor but it works with AC, which a transistor doesn't)

as for keeping time, I think the easiest thing to do would be to use an already existing wall switch timer to power the whole circuit. When the circuit is powered, something would generate a PWM signal with an increasing Duty Cycle, which would drive the triac...

simplest would be to use a microcontroller, but it could also be done with some basic logic (lm555, counters, comparators?)

hope this gives you some ideas if you were looking into building one yourself

if you want to buy one, then I'm not exactly sure if this exists or not (sorry)

 

[OSX]

Here's a basic idea I came up with. The timing of this is all controlled by a basic RC network. The capacitor slowly charges. When the voltage across the cap hits the lowest voltage you want to run the light at, it turns on an SCR, which supplies power to the triode. As the voltage increases, the triode puts more voltage on the lightbulb. However, once the RC network reaches the maximum voltage, a transistor opens up and dumps the voltage on the RC network to ground. While this happens, another SCR opens up to supply the maximum voltage, because the triode will sense zero voltage on the gate. I'm no EE, just a high school student, but this should work (probably with some modifications.)

Text