I want to create a keyboard that lights up individual keys when you press them and then slowly fades them away. I don't know how exactly to do this but I was talking with a friend and we though of using a capacitor in conjunction with a transistor to act as switch to turn the LED and then turn off when the capacitor is discharged. Now I know very little about electronics and am not even sure if this will work. I just need confirmation if this will work and if anyone else has a better idea then please tell me.
Hehe, there's a couple of threads along those lines that I was reading earlier. You're in for some effort if you go for that, because from everything I've seen it's a lot of work.
its going to be oodles of work. But a slow fade is fairly straight forward using capacitor + resistor. but all 102 keys? lotta work, u could make it novely of the space bar or somthing.
How would it be possible to find the time that it would take for the capacitor/resistor to discharge from full to, say, one quarter voltage?
I really don't plan on doing all 102 keys. I probably might only do like 50 keys or meybe less because there are many keys that a fade effect wouldn't make sense for. WASD definately needs to have it and I think all of the letters should have it and the arrow keys. I don't know about doing the numbers or the secondary icons on the right side of a keyboard. I also realize it will take a lot of tedious work but I don't mind doing that, most of my past mods have taken weeks to complete, I just do a little at a time and see how far I can get. You won't believe how tedious it is to paint a motherboard with UV paint using toothpicks . I might start this over Christmas break but I don't have the tools at college to probably finish it before summer.
t = R x C x 1.25(ish) Where R = resistor value in k and C = capacitor value in uF giving t = Time in ms
Remeber the LED will turn off when there isn't enough voltage! Because of this u won't get a completely smooth effect but it might look cool enough once its shining throw the keyboard plastic.
how would i wire a capacitor to a led, parallel or series and how to find what size cap for 5 3mm red leds?
For fade-out only, the capacitor goes across the led & series resistor (=across the power supply). Not really recommended, as switching on gives a big surge on the power rail as the cap charges. For fade-in and fade-out, you need to use two series resistors adding up to the value needed by the led/supply, with cap connected between the middle of the pair + led, and ground. The cap charges through one & discharges through the other & the led. Using a transistor connected as a voltage-follower means the needed capacitor can be G times smaller, where G is the transistor gain. I'd draw a picture if it wasn't bed-time.
^ crude up & down fade ^ using a transistor for slower fades with small caps. You'll need to experiment with values to get the effect you want. Use a low led current or you won't see any change for most of the fade time.
Thanks cpemma those schematics are helpful. I got the keyboard apart and I am pretty sure the touch senser won't active if I put a small surface mount pushbutton switch and a surface mount LED over the touc button. Next I just need to wire up one and make sure that it will work then I have a lot to do if I can get one to work. EDIT: Well I went to radioshack and bought the equipment for a mock-up of the second diagram which cost me and arm and a leg there. They should call it rapeshack. Well anyways I did a mock up and seems to work well I am going to leave a 3mm led wired with the push button down for a while to see if anything occurs. I got the keyboard apart and I plan on using push buttons over the top of the pressure sensors and was thinking about using surface mount LEDS to light up each individual key. Was wondering what everyone else though of that for an idea. One question though the typical forward voltage for a surface mount LED is 1.85 with a max at 2.3 Now I don't really know much about electronics but I was wondering if I should use different resistors with this different value. The 3mm I got in there seems to be fine and I don't think it is at full brightness. I really need a multimeter but I don't have one. And Just one more thing the surface mount LEDs ar ethe most expensive part of this. I am looking for red ones and am wondering if anyone else knows of an extremely cheap place in the US for surface mount red LEDs.
