using an alarm clock to slowly turn on light

[nkaufma]

I would like to use the alarm output of my alarm clock to turn on an AC light slowly at a variable selected rate, similar to the sunrise alarm clocks. I was going to try using a 555 as a schmidt trigger, and then would have to use a scr on the output. Can somebody help me with this? Thanks

[Chris Smith]

I remember answering this a year ago? Use a slow gear motor to turn on a light dimmer. Gear/pulley it acordingly and use a 555 if necessary to slow down the motor speed? Any contact from the clock can start this proceedure.

[L. Daniel Rosa]

Wow! This sounds just like a project I've been fantasizing about. I'm getting ready to jump into microcontrollers, but need purpose. I was over at a friend's house the other day and this one came up. If you like I'll keep you posted.

[nkaufma]

That would be great! Thanks

[cato]

Sounds like you have it, what part are you looking for help with? As I recall, if you ramp up (or down?) the voltage on the gate of the SCR, it will increase the percentage of the AC cycle that the scr is conducting and that will increase the light output of the lamp you are driving with the SCR. I forget....but you might have to worry about voltage isolation in going from your timer/(integrator?) circuit or microcontroller circuit and the SCR gate. <p>Be Careful

[nkaufma]

The only part I'm not sure of yet is the output of the 555. What circuit can I design to ramp up the voltage on the gate of the SCR and control the ramp timing with a pot.

[L. Daniel Rosa]

It's a matter of timing, not ramping voltages that controls an SCR (or TRIAC) for lamp dimming. The pot in a dimmer controls the current charging a capacitor that goes through a trigger device (usually DIAC, sometimes neon lamp or SIDAC) to the gate of the thyristor.<p>This can be approximated with an optoisolator (with transistor output, use two- it's AC) in an otherwise ordinary AC dimmer with some tweaking. This will take a ramping voltage for the dimming control. One option for this is a 555 into a 4040 (CMOS ripple counter), an R2R ladder on the 4040 outputs (at least a few of the most significant bits, 10k and 20k seem like reasonable values for CMOS to drive) with an opamp as a unity gain buffer to drive the LEDs on the optoisolators. I'm sorry I didn't say as much earlier, time crunch ya' know.

[frhrwa]

www.smarthome.com already has it.. cheap..

[Ron H]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by wayne:
www.smarthome.com already has it.. cheap..<hr></blockquote>
Which product?

[cato]

I understood your original post to imply that the output of the 555 circut would be a signal line going from zero to VCC and staying there after some period of time explires.<p>If thats the case, then you can use that output to generate the "ramp" by connecting the output signal to a resistor of large value (1 megohm?) and connecting the other end of the resistor to one end of a large capacitor (10 UF?). The other end of the capacitor would be connected to common.... The voltage at the point where the resistor and capacitor are connected will ramp up slowly (over a matter of seconds using the values I suggested). Depending on what you want to connect the ramp to you may need to buffer that signal so that the load doesn't consume the tiny current flowing through the 1 meg resistor.