Fading eyes

[samwise]

I have seen circuits for "fading eyes" where 2 LEDs fade in and then out over a period of time (NE555). I have 10 LEDs and would like to build a circuit to fade in and out over a 12 hour period (LEDs go in fish tank and I would like to simulate a moon cycle - I know, a little much...). Any ideas? Can I modify the fading eyes circuit w/ resistor/capacitor to increase period? Thanks for your help.

 

[akg]

I have seen circuits for "fading eyes" where 2 LEDs fade in and then out over a period of time (NE555). I have 10 LEDs and would like to build a circuit to fade in and out over a 12 hour period (LEDs go in fish tank and I would like to simulate a moon cycle - I know, a little much...). Any ideas? Can I modify the fading eyes circuit w/ resistor/capacitor to increase period? Thanks for your help.

i think the attachment will work as u expect
R is a resistor the C is a high val cap, X is a led , remember the max o/p current of 555 u may need a current limiting res too.

 

[ljcox]

12 hours is a long delay for a 555.

Besides, it won't be very accurate and you will need a large capacitor.

It would be better to use either a PIC or a counter.

 

[akg]

12 hours is a long delay for a 555.

Besides, it won't be very accurate and you will need a large capacitor.

It would be better to use either a PIC or a counter.

oops sorry i missed the 12hr part

 

[Russlk]

If you are using 10 white LEDs in series, 35 volts plus current limiting resistor is needed. 10 LEDs in parallel will need 10 current limiting resistors and about 5 volts & 100 mA drive. An 8 bit binary counter and crude D/A will provide a 12 hour cycle. Do you want 6hrs brightening and 6 hours dimming or 12 hours brightning and 12 hours dimming?

 

[ljcox]

Further to Russlk's suggestion. You could use a 4020 CMOS counter. It has 14 stages, connect a R/2R digital to anologue converter to the last 8 outputs.

Connect an emitter follower to the output of the DAC with series/parallel strings of LEDs and rersistors from its emitter.

The power supply could be 12 Volt since the 4000 series CMOS can operate at up to at least 15 Volt.