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aquarium lights

Basic aquarium lights based on 555, MOSFET and leds.

Presentation

Principle

I was a shameless sinner who made aquarium lights with a resistor to limit the current and a boost converter. I have no excuse. And when the powers of the aquarium decided that water spash would finish eating the copper of my connector, I understood the message from above (well, below in that case since the water is below the leds): make it right.
So I'll use a proper power source, with led strip (still) and PWM modulation (which means 555). Basic circuit, but the best answer to a basic need.

Points of interrest

555 and PWM made simple: honnestly I didn't find aywhere on the net any simpler PWM with 555 circuit. 2 resistor, 1 cap, 1 diode and you get a range from 1% to 99% duty PWM, this is the simplest 555 PWM circuit I could find. Just what you need in most cases. Other circuits have more parts without being that much more complex to be honnest. Let's use this one and see.

The idea is to set the simplest possible astable 555 oscillator. One other very similar circuit is here, with an online calculator.
In a nutshell, the key ideas are (from above site):
  • Increasing C will increase the cycle time (and hence, reduce the frequency).
  • Increasing R1 will increase Time High (T1), but will leave Time Low (T0) unaffected.
  • Increasing R2 will increase Time High (T1), increase Time Low (T0) and decrease the duty cycle (down to a minimum of 50%)
  • Implementation

    Bill of materials

  • MOSFET x1: IRFZ44N power N-Channel mosfet => sink (what I had in my toolbox to be clear, thank you eBay)
  • 555 x1: The 555
  • Resistors for PWM: R1 = 100ohm, R2 = 100ohm
  • Cap for the PWM: C1 = 0.1uF
  • Diode: source diagram calls for a Schottky diode, but a regular simple diode works just fine and makes no difference as per my tests. So I go for the cheap one.
  • Potentiometer (I used a 5k Ohm one but any other value should be ok maybe? try and tell me)
  • A PPTC (resettable fuse) of 0.5 A, just in case, since we're putting water and electricity quite close. A fuse on the main would have been a nice touch too.
  • 12v1a power supply I bought in HK years ago
  • A strip of white leds I don't remember I bought but thanks SeeedStudio anyway
  • other misc bling bling, caps for power stabilization, leds, screw connector, etc...
  • Settings

    With a measured duty cycle of 50%, we're at about 5-7kHz (forgot exactly), and with a bit less than 2 meters of white led strips we have a comsumption of 0.47A at 12V (says my power supply). It's bright enough, and after a couple hours of continuous running, the "hottest" component was the 555 that went lukewarm. All the rest and especially the MOSFET staid at room temperature.

    Schematics


    That's what I made↑
    Nota bene:
  • D1 doesn't need to be a Schottky, any cheap diode works. But it's necessary or you won't get less than 30% duty.
  • R3 is necessary to stop the enormous ripples! without it you can get +30v-10v swing !! Just put it, something between 100-500ohm seems to do the trick (I used 510 ohm in my final design) -> Thanks to Great Scott video for the tip! I noticed the ripple but didn't know how to fix.
  • Source code

    None in this case, there's no mCU.

    Pictures


    The circuit on the simple PCB in shape of breadboards. Love these for simple circuits.

    Links

    Helpful sources

    Inspiration

  • 555 PWM driving a MOSFET http://www.instructables.com/id/PWM-dimmer-using-NE555-and-MOSFET-with-DIY-alumini/step3/Circuit-diagram/
  • Simplest 555 PWM circuit http://www.instructables.com/id/Yet-Another-Simple-Pot-controlled-555-PWM-generato/step2/What-will-be-needed/ (original source of the source)

  • Nota Bene: if you follow this link you'll find a simpler version with only 2 resistor and 1 cap BUT the minimum duty cycle I can get without the Schotky diode is 30%-ish (100 ohm/100ohm/0.1uF). With a simple Schotky diode, you get a 1%-90% duty easily.
    All content on this site is shared under the MIT licence (do what u want, don't sue me, hat tip appreciated)
    electrogeek.cc ~ Formerly known as Kalshagar.wikispaces.com (AlanFromJapan [2009 - 2017])