I am working on Company and we are looking to make LED candles that can be blown out atop the fake cake.
I am looking at using the Arduino Mega 2560 Rev 3. I am not familiar with the equipment and have seen some designs where people have just blown on the LED's to lower the heat level or others where they have use a microphone to detect the sound/breath.
I also was curious about the wiring and if it is possible to wire multiple LED's to the same head pin and such.
I would love to chat if you have done a project that is similar to this.
The key is the detection of "blowing". Al ightly heated, obviously current consuming, resistance strain could be one way to go.
The rest You do from an Arduino beginners kit examples.
I have looked at that and I am confused as to the possibility of wiring multiple LED's to the same pins so that I can wire about 35 candles. I have tried to look at videos to see if someone has wired multiple LED's to the same pin but have not come across one yet.
We are trying to figure out what we all need to order so the department can place the order for the University. I have not been able to get my hands on an actual Arduino yet
I have looked at that and I am confused as to the possibility of wiring multiple LED's to the same pins so that I can wire about 35 candles. I have tried to look at videos to see if someone has wired multiple LED's to the same pin but have not come across one yet.
In principle you can wire many leds in parallel with a resistor for each.
In practice it may take a few amps and a MOSFET to switch them ON/OFF.
In retail that is how cheap one color led strips work.
I would make the candle tubes work as pitots to suck something into moving down in the tube and detect that. Put a straw in a glass of water and blow over the top to see how a primitive pitot tube works. Blow too hard, the water will spray out.
I would want to make each "candle" work independent but that would take a lot more work than 35 leds and 1 sensor.
I might also want the candles to flicker unless the fake cake is too chintzy.
Probably the best idea: A tube down the candle, with a microphone mounted at the base.
Actually, there are electret microphones sufficiently small that could be mounted in the "candle" itself, just below the LED(s). The microphone has to measure the loudness of white noise.
Here is what we have come up with so far. We are looking to wire about 23 LED's that have the following specifications:
Color: Yellow
Peak Wavelength: 590 nm
Package: Round 3 mm
Lens type: Milky-white
Viewing angle: 50 degrees
Intensity: 900 mCd typ. at 20 mA
DC forward current: 30 mA
Forward voltage (typical): 2.1 V
Lead-free (RoHS compliant)
Manufacturer: Betlux Electronics
Manufacturer part number: BL-L314UYW-B-S3
We are looking at the Microcontroller ATmega2560
Operating Voltage 5V
Input Voltage (recommended) 7-12V
Input Voltage (limit) 6-20V
Digital I/O Pins 54 (of which 15 provide PWM output)
Analog Input Pins 16
DC Current per I/O Pin 20 mA
DC Current for 3.3V Pin 50 mA
Flash Memory 256 KB of which 8 KB used by bootloader
With what I have read it seems like this will be a better solution than what we had been originally thinking of and that this would work.
Not sure what type of resistor we would need yet though. Still researching that today.
I probably would have uses the A/D in EXTERNAL mode, with the Aref pin connected to the 3.3volt pin.
That would have increased sensitivity by 50%, assuming Vf of the LEDs is <= than the 3.3volt supply of the Uno.
My averaging tests in other projects showed no benefit over ~45 samples, so 256 samples...
Leo..
Mega2560 DC Current per I/O Pin 20 mA is a good number for continuous operation and 30 mA still works but if you think you can get that out of many pins at once, the pins in and out max total for a short time is still 200 mA.
So you have to power the leds either external to the board or keep within about 100-150mA total at any cycle, like 5 leds at 30 mA ea.
12V with a resistor will drive 3 white leds. I have 12 led disks that run on 12VDC or AC, G4 replacements for sodium bulbs.
I powered them with a 12V supply, making sure to connect the supply ground to Arduino ground and used Arduino pins to control 2 small power FETs (they were 50 for $500, 250 mA max) to blink 2 disks opposite, they ran hot on straight 12VDC.
The white leds drop 3V each, the rectifier (to run on AC) drops another 1.4V and the 51 Ohm resistor is a poor current limiter vs the change in led Vforward as the disk heats up, that's why the run way hot.
A DIY leds in series wouldn't have the rectifier and you could maybe get 4 yellows on 12V.
Leds in series use the same current by adding voltage, leds in parallel add current not voltage. G4 disks have leds in series in parallel.
Total chip current (not pin or port current) for a Mega is 400mA, the Uno is 200mA.
But yes, 35 LEDs should be powered externally.
Already said that upscaling is not for beginners.
Can't use the LEDs in series on a 12volt supply, because Vf of each individual LED needs to be measured with respect to ground.
As said, the LEDs need to run hot for the detection of a temperature (Vf) drop when blown on.
Leo..
Wawa:
Can't use the LEDs in series on a 12volt supply, because Vf of each individual LED needs to be measured with respect to ground.
Vf is measured across the diode. The drops add, this has been discussed on the forum more than a couple times too.
All voltage is electrical potential between points. Ground is always relative and no not everything is plugged into Earth or is influenced by Earth ground.
Leds in series lets you run multiple leds with the same current, though proper design says use constant current circuits.
I have led disks, the traces are visible, yeah 12V runs 4 chains of 3 leds using 3W 12V full bright.
GoForSmoke:
Vf is measured across the diode. The drops add...
Sure, but those three added tiny variations are superimposed on a ~10volt stacked LED voltage.
And the Arduino can't measure that without a voltage divider, which also lowers that variation.
Blowing 100% on three LEDs at the same time might also not be possible.
Leo..
Wawa:
Sure, but those three added tiny variations are superimposed on a ~10volt stacked LED voltage.
And the Arduino can't measure that without a voltage divider, which also lowers that variation.
Blowing 100% on three LEDs at the same time might also not be possible.
Leo..
The same case applies when using a resistor to current limit a single led. The drop over the resistor has to be big enough to balance the change. Grumpy Mike has more about the subject in his leds tutorial: http://www.thebox.myzen.co.uk/Tutorial/LEDs.html
... snip ...
V_total - Vled_turn_on = R * I
... big snip ...
Warning
Note that these calculations only really work for when the resistor is dropping a good percentage, at least half, of the voltage across it. ... snip ...
Led Vf lowers with temperature, more current flows as V/R grows. But pick the resistor to match or exceed operating condition Vf and current won't run away.
Don't need to teach me. Worked with LEDs of all sorts for many decades.
I even build my own WiFi LED driver boards for up to 16 12watt downlights (ESP8266 on the bottom).
But you seem to have forgotten that this post is about blowing out a single LED with human breath.
A tiny LED that HAS to be hotter that that human breath, so a tiny rise/drop in Vf can be detected.
Don't want to hijack OP's thread anymore for this.
Leo..
kingja1:
we are looking to make LED candles that can be blown out atop the fake cake.
I am looking at using the Arduino Mega 2560 Rev 3. I am not familiar with the equipment and have seen some designs where people have just blown on the LED's to lower the heat level or others where they have use a microphone to detect the sound/breath.
I also was curious about the wiring and if it is possible to wire multiple LED's to the same head pin and such.
Not quite the same spec.
The hot led has a shorter life, that candle burns out quicker.
It is neat, analog read between resistor and led requires no extra components but wire.
If the candle lets the led be replaced easily without tools, led life matters less. Socket candlestick?
