i have a crstalfontz 20x4 lcd. i currently have it next to my bed and my computer on the other side of the room. i have thew display showing winamp info song title song time current position and some system info, only problem is the back light tedns to keep me awake. i have the power for the back light wired up to a 5 volt dc converter pluged into my wall (110 VAC to 5 VDC). i want to put a push button switch next to my bed for the back light. push it and the back light comes on for maybe 5 seconds and then i want it to slowly decrease the voltage so instead of just turning the backlight off it dims it out. hell getting it to dim in then stay on for 5 seconds then dim out would be even better. all done through voltage regulating. a passthrough in other words. power into the circuit then power from curcuit to the LCD power jack anyone know how to do this?? i know a little about electroincs but not a lot. Recap :: push button backlight dims up stays lit for 5 seconds then dims out. hoping to do this without modifying the display itself. anyone able to help me with this?? /me prays the god of Bit-Tech electronics reads this and grants me his wisdom.
umm, not sure about fading out, dont kow how to do that, maybe someone else will... what about a toggle switch, so you can just switch the backlight on or off, simple as... .icecube
yeah i know i could do that but its not very cool and i wouldnt call droping a momentary on the line modding =) lol any way its hard on the eyes when the room is dark and then pop AH BRIGHT LIGHT OH GOD MY EYES I CANT SEE but if it fades in and out its easy oin the eyes. like some of the new cars when you close the door the dome light fades out.
im guessing the solution lies in using capacitors for that, they are the things that store voltage like a "voltage bucket" then release it slowly, so they would leak the power out after the switch went off to the circuit and slowly dim it, like a led on say a monitor u switch off at the powerpoint
SileNceR basically has the right idea. It would be fairly simple to connect a capacitor in parallel with the LED backlight. The only question is what size capacitor. To calculate it, you'd need to know the effective resistance of the circuit, and you probably just can't know it. So I'd recommend trying some different values of electrolytic capacitor in the 100-1000 uF range to see how they behave. Some stores (including Radio S*ack) will sell you a capacitor 'grab bag' for a couple of bucks, I'd recommend that as opposed to buying individual pieces from a catalog. Just for fun, the dim time is 5*tau, where tau = R * C So a five second dim time implies tau = 1, and I'm guessing the resistance to be on the order of 1-10 kohms, which is why I'm recommending a cap in the 100 - 1000 uF range, if you follow me.
i dont want a 5 second dim i want the screen to stay lit for 5 or 10 seconds then fade out. id like to get it to fade in too but i can deal without that. what i really need is the schem.s for a time switch push the button the timer starts when the timer gets to zero turn off. i want to do this all in hardware without need for the PC to handel the program, im sure macroman or linear knows how to do this but i cant seem to get them to reply. but the cap. idea is great i hadnt thought of thaT. thanks all for the help all i need now is the timing scherm for the switch and if posable a schem. for the power to slowly increase up to 5VDC Ramp up to 5 VDC start timer when timer ends Ramp voltage down for 5 VDC to 0 VDC do all that with ICs hopefully without needing to program the chip. thanks again for the help guys
oh sorry linear didnt recognize the new avatar. got any ideas for the fade in and or timed switch?? <---- monica lewinscy Emoticon???
I'd use a 555 timer connected with a large (4000 uF or higher) capacitor and a resistor of 50-100 (or more?) K ohms. The timer will produce a pulse of as long as you want when activated by an external pulse (from a switch). Connecting the capacitor/resistor network to the circuit will provide the fade in and out. Is the pin for the backlight the one it takes power from or the one that controls it?
viridius has the right idea. Use a 555 as a one-shot, and use the cap idea in conjunction with that for a fade. Either Google for 555 for the details, or eventually someone will be sure to show you a diagram of how to hook it up.
This should give you something to experiment with. I have not made these circuits only quickly jotted them down off the top of my head. This one uses a latching push on/ push off switch . The on/off delay is determined by R1/C1 and I leave you to find the best values. You will find the calculated values quite inaccurate due to the circuit design. R2 is to ensure the transistor stays off when it's supposed to. It should be a high value at least 1M. This uses a simple non-latching push button. This uses a D type flip flop as a latch allowing an ordinary PB to be used. R3/C2 is to prevent switching spikes. A flip flop would be a better way of doing it but I am keeping this circuit as simple as possible. These circuits are meant to be a very simple solution and not an exercise in circuit design but they are simple and cheap enough to experiment with. Might be worth trying a Darlington transistor since it's base current will be less than a standard one. Assuming the leds require 5V I would suggest running the circuit from 7V to compensate for the transistor volt drop, especially if you use a Darlington. These circuits give a fade in/out. Replace the flip flop with a 555 timer in one shot mode to get the exact action you want. i.e. press buton and display fades in holds for a time and then fades out. Try R3=470K C3=22uF for 10secs (I did rush them )
You guys rule viridius thank you for the great ideas Linear thanks fore the input and macro i cant thank you enough for the schems if i do get them to work right il build you guys one and send um to you. thanks for the help
A positive-edge triggered gate will swing the output whenever it recieves a pulse. It makes a momentary switch into a push-on, push-off switch.
Can you not go to a local scrap dealer and hack out the circuit in a car that fades in the dome light, then fades it out after a few seconds.? It's 12v!!
