How to fade a led in over 10 minutes, using cheap ic's?

I want to fade in 4 leds over a period of 10 minutes then have then turn off after another 50 minutes or so, voltages of leds dont matter. Any ideas would be great! Thanks Cybot

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frollard8 years ago
First thing that comes to mind is a fairly large capacitor, that charges from source when you apply power - it slowly discharges through a huge resistor...and a transistor 'reads' its voltage and powers the leds from the power supply. Tweaking the resistor would adjust how long it takes to fade.
Cybot Rules (author)  frollard8 years ago
can You give a estimate of the values or a link to somewhere with a schematic / equation?
Off top of my head no...I hadn't put that much time into thinking about it :( google 'bowdens hobby circuits' - you can learn a lot by studying how those work.
Cybot Rules (author)  frollard8 years ago
i have built the circut "eyes" but cant seem to adjust the rate of fading, any ideas?
AndyGadget8 years ago
You could do this quite easily with a Picaxe 08m chip which would cost around 2 dollars. It's a programmable microcontroller which is programmed in a BASIC like language straight from your PC, and will drive up to 75mA if you tripled up the outputs (or as much as you like if via a transistor). The program would consist of nested loops, using a PWM (pulse width modulation) method to increase the brightness.
Total component count would be 3 resistors, one LED, one (8 pin) chip.

Cybot Rules (author)  AndyGadget8 years ago
Is there any pre programmed chips comercially avalible, as i want it to be so that when they are purchased i just connect then to the circut and they start, as this a project designed to be mas produced... Thanks so far :)
Nothing 'off the shelf' which I know of for something that specific, but for that sort of delay a microcontroller is the way to go. The PicAxe 08 would come down to around 1 dollar 60 for quantities of 250 or more. If you went for a standard PIC solution, it would be cheaper but harder to program.
Cybot Rules (author)  AndyGadget8 years ago
Is there a way to mass program them?
What sort of quantities are you thinking of? For very large quantities the most cost-effective way would be a custom die chip (ASIC). I've no idea what the breakpoint would be, but the initial tooling cost of that would be very high.
Cybot Rules (author)  AndyGadget8 years ago
Its meant to be designed for 1000+
Cybot Rules (author)  Cybot Rules8 years ago
Ive made some code - I have a Arduino- so how would i make the arduino sketch into a format for flashing onto PicAxe?