I'm working on an Arduino project. My electronics knowledge is far below the level it should be, so I thought I'd post my circuit here before buying all components, so you guys can tell me if it's okay, before I fry my arduino.
I want to flash 3 high power leds briefly. I do not need any PWM support (however if I could use it that'd be a plus!), the leds will be flashed on full power about 3x (300ms) in 4-5 seconds, three seconds delay, then they would repeat the cycle. This cycle would happen not too often. It's event triggered (triggers when the doorbell rings/loud sound is heard/.. so it shouldn't trigger too often.)
Would I need any additional heat sinks?
I would like to know if the schematic below would be the correct way to go:
My apologies for the yellow paper, didn't have anything better to scribble on.
Thank you for any and all replies!
EDIT:
I have several throw-away cameras lying around here. If possible at all, I'd much rather use the flash module that's fitted into these cameras, however I don't have the slightest clue how to go about this. If anyone could point me into the right direction, I'd be infinitely grateful.
That constant current driver looks interesting to me, thank you for pointing it out!
So, the circuit would be as following?
How much power should the 1050Ohm resistor be able to dissipate?
I would prefer your first circuit but instead of using a NPN power transistor I would use a power N-Channel MOSFET.
The right device will have a very low Rds(on), so the voltagedrop across the drain-source will be a few tenth's of a volt at most. The 6.8 ohm resistor is exactly right for limiting the current to less than 500mA. Because of the low Rds heath will be neglectable in your application.
Because a MOSFET doesn't need any current to the gate , you can use almost any resistor-value between Arduino and Gate, so 10kohm will be pretty safe.
You need a mosfet type with a Vgs of less than 5 volt to be switched on fully by Arduino.
Good types are 05N03L and similar types like 06N03, 09N03 or P2804
Besides, a.t.m. these mosfets are cheaper and easyer to get than the Cat4101.
I would suggest that attempting to use a flash module from a throwaway camera might well be the last thing you will EVER DO.
There is a power supply in that device that charges a .1 to 4.7 uF / 450V capacitor to ~350 - 400V and that capacitor WILL hold a charge for days... Voltages of that level are FATAL... the usual thing that happens is that the shock drives the heart rhythm into fibrillization or an irregular heart rhythm where the heart muscles don't work properly... If AT ALL.
I've been an engineer for 40 years and those types of devices are things I won't ever attempt to hack or "Repurpose". It's dangerous just to open one if you don't know exactly what you are about.
when I need an HV power supply for a flash unit I buy a module intended for that purpose...
Never, NEVER attempt it by your self. You can buy external slave camera flash units with safe means of triggering the flash or a strobe light to do what you indicate you wish to do..
Commonly available used from various sources for perhaps 20 - 50 dollars...
Again, thanks for the replies. I have looked into MOSFET's but I can't grasp how they work.
I'll just believe you on your word and use one of the example MOSFETs you gave, as the price is indeed lower.
If anyone has a better idea to make clearly visible and noticeable (across the room) flash sequences with an Arduino, which are cheaper than the solution I would use now, using high power LEDs (which are actually pretty pricy) and a MOSFET, please say so.
I already know about the dangers of the high voltage capacitors. I have researched them before, as I am an amateur photographer in my spare time. I took that into consideration before asking my question. But after asking the question I went to have a quick look at the disposable cameras, and noticed they don't have a flash at all.
So no worries, I won't go that way.
Thank you for all the replies again, I really appreciate them!
Thank you for the schematic, however, I would rather build something where I truly understand what I'm doing, and those schematics are getting too complex for me to understand.
With a MOSFET use a 150 ohm gate resistor (you'll get more efficient PWM that way
as it can switch a lot quicker). Adding 10k from the pin to ground will hold the MOSFET off
during start-up time (before the pin gets set as an output).
Its essential that the MOSFET is "logic level" if its driven from 5V, and you need to choose
one with a low-enough Vds(on) - a low-enough value means no heat sink needed.
The CAT4101 circuit 1k resistor isn't dissipating significant power at all, its programming
the output current. The CAT4101 encapsulates a constant current circuit in one device that's
easier to use (althought its possibly only available as surface-mount). Heatsinking the CAT4101 has to be thought about (calculate the disssipation).
pearldragoness:
How much power should the 1050Ohm resistor be able to dissipate?
There's only a milliamp or so of current here; the resistor size is not important. The CAT4101 itself is dissipating all of the power, and it is capable of 3W max.
It's a linear (vs. switching) driver so it's really just a fancy package equivalent to using something like an LM317 for constant current. The advantage of the CAT4101 is that, by comparison, it has a really low dropout voltage. But then that's only valuable when your input voltage is very close to the voltage needed by the LEDs.
pearldragoness:
Isn't it possible just to wire it up like this:
And if not, why not?
Thank you <3
Yes, but don't try to PWM it with a 10k resistor on the MOSFET.
6.8Ohms doesn't leave much margin for error in the voltage calculation. Use a power supply with an adjustable output so you can tweak it. And make sure the resistor has plenty of watts to spare.
