My grandfather likes to build all sorts of models and this time he wants to make a lighthouse. I thought it would be great to make it come alive by putting a led inside that pulses just as the original lighthouse does (twice every 14s). Arduinos are however quite new to me and I'm having some difficulties to combine all the different components. Writing the code should not be a problem though.
The end result should be something like this:
The LED that I want to use requires 3.0V and 300mA. So I understand that it should be powered from a different circuit and controlled by a MOSFET(or transistor?) connected to the arduino.
I was thinking of using an arduino pro mini, but I don't know if I should be using the 3.3V or 5V version. In an ideal case the whole thing would be battery powered, preferably with simple alkaline AA batteries (max 4 would fit inside the lighthouse). I read that the 3.3V version is more power efficient, so that one would probably be better if it is battery powered? How long it lasts on batteries is not really a big concern, the light will probably not be on very long or very often.
So lets say that I would use 4 AA batteries. That should give me 6V (or 4.8V). Could I power an arduino pro mini directly from that?
The LED requires 3V so I guess I need some way to drop the 6V to 3V. I read that using resistors is not really advised for high power LEDs (or is this LED still low power enough to use a 10ohm resistor?). Ive seen some LED driver circuits, like ones using the lm317, but I dont know if 6V (or 4.8V) from 4 AA batteries is large enough as input voltage to get a stable 3.0V to the LED.
I also have no clue about which MOSFET/transistor I should be using (and probably depends if I use a 3.3V or 5V pro mini?). The person from the blog used a IRL520 MOSFET together with a 10k resistor. Would that work in this case?
Please post a link to the LED product page or data sheet.
4XAA is fine for powering an Arduino, but won't last long unless you use sleep modes, and an Uno is lousy for this.
A "bare bones" Arduino should run for a year or two on 2XAA and still blink an LED every 14 seconds. There is a great DIY tutorial here.
You would still need a transistor and resistor to switch a 300 mA LED, the details will depend on the datasheet. On the other hand, that would be a blindingly bright LED, intended for room lighting. Are you sure you don't want to use a standard, low power white LED?
Thanks for the link to the bare bones arduino tutorial, I will have a look at it!
I thought it would have been nice to have a nice bright light, but maybe you are right. I think Im going to keep it simple to begin with and save me the headache..
I agree with jremington about the 300mA led. A led like that requires a constant-current driver and a heatsink. I think it would look too bright and not right for a model lighthouse. But a number of 5mm high-brightness white LEDs (12 or more) arranged in a circle, facing outwards, connected to the Arduino's pins could be used to make a display that appears to rotate like a real lighthouse.
If you just want to blink an LED, look into the LM555 timer chip. It's a lot cheaper and you don't have to program it. (You set the timing with resistor/capacitor values.)
I also "feel like" a 1W LED will be too intense, but it might be OK for a large outdoor model.
[u]Here[/u] is a little switchmode constant-current LED driver. This one is dimmable with PWM or it can be switched-off so you wouldn't need a MOSFET.
As a general rule, you shouldn't use a current-limiting resistor or a linear regulator (like the LM117) for high power LEDs (1W or more). I don't know how much "extra" voltage the LM117 needs. A resistor and the LM117 will both get hot. The main difference is the active constant driver will hold constant current (and constant brightness) as long as it's working within spec. With a resistor the LED will get dimmer as the battery drains. With a higher voltage (more power dropped across the resistor) the dimming will be less exaggerated, but the resistor will get hotter with more voltage. The LM117 will also get hotter with more voltage.
I've never used the LM117 circuit, but there might be a way to enable/disable it without a MOSFET.
or is this LED still low power enough to use a 10ohm resistor?).
If you have a 6V power supply (battery pack) 10 Ohms would be correct. (3V across the resistor and 3V across the LED). 3V across 10 Ohms is 300mA which is about what you want. And, that's about 1 Watt, so you'd want a 2W resistor (to leave some safety margin).
I suspect a regular LED that works on 5 or 10 mA will be fine. Having a really bright light in a model lighthouse would just be irritating.
Real lighthouses do not flash their lights. Instead a mirror and lens rotates and what appears as the flash is the brightness when the mirror/lens combination faces you.
I think if I was making a model lighthouse I would replicate the flashing by using a low-geared DC motor to rotate a small piece of mirror. Of course a motor would consume a lot more power than a flashing LED. But perhaps it would be neither necessary nor desirable to have the model lighthouse flashing all the time.
I'd say.. for the price and time of making a standalone Arduino compatible circuit...
you can just get an Arduino Pro-mini for $2.00 off ebay.
A nice HB 5mm white LED will be fine for your needs.. (no need for a high powered led here)
If the timing is super crucial, you may want to look into adding an RTC (real time clock) module... but I'd imagine using an internal counter/millis would be good enough here.
Once you get your board... and simple FADE LED tutorial will get you to home base!