This is about an arduino binary clock. Please check the schematics. Wired the LEDs through transistors. Not sure whether to use resistors or not. The LEDs seem to be functioning alright without resistors. But the problem is that they all light up with different brightness level.
Should I use resistors to try and balance that out? I checked the "ElectroDroid Pro" android app and tried to use LED Resistor Calculation. I put in Voltage Drop (3.2 V), Forward Current (350 ma), Power (1W) and it gives me a resistor value of nearly 1 ohm. Now, the app does ask you how many LEDs you are going to use, but it only asks about the number of LEDs to be used in series. There is no way to indicate that you need calculation for 13 LEDs which is in my case. Can you help?
I don't have seconds. The clock is HH:MM format with 4 column setup. 2,4,3,4 on each column respectively. Excuse my lack of knowledge about electronics please.The LEDs that get most bright are the ones on the right hand side. I'm guessing that is because the minute LEDs are powered on most often therefore they warm up and draw more current.
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Please check the schematics
What schematic? All that is posted is a physical layout diagram.
The LEDs seem to be functioning alright without resistors.
No, they are being damaged.
You can not drive a high power LED with a simple transistor and resistor, you need a constant current driver.
Grumpy_Mike:
What schematic? All that is posted is a physical layout diagram.
No, they are being damaged.
You can not drive a high power LED with a simple transistor and resistor, you need a constant current driver.
Thanks. Sorry. I meant the general layout diagram. I don't have schematics. But what exactly do you mean by "They are being damaged"? I have been running the clock to test it for the last 24 hours and it is still going strong. Please explain. I have a separate power supply for those LEDs that is capable of supplying 3.0 Amps at 3.4 volts.
When you put more than the maximum forward current through an LED it cuts down the maximum brightness it can give. The more you do this the more damage it will do. Their is a concept known as the half life, that is the length of time it takes to reduce the brightness by a half. You are caining those LEDs and they have already suffered damage.
You can not detect this by eye after only 24 hours but if you had the equipment to measure it my guess is that you have already lost about 3%. Also LEDs treated like is are more prone to fail prematurely, say after one year instead of 20 years.
Driving an LED without any effective current limit is damaging them.
Hi. I have made a binary clock with high power LEDs.
The power source is 3.4 V. Forward voltage of LEDs' is 3.2V. Forward current is 350 ma. I have done the calculation and used 1.2 Ohm resistors with LEDs. Do you think it will be fine?
Someone was telling me without an LED controller, LEDs are as good as dead. What do you think?
Because arduino itself cannot handle the current I have used a separate current source for the LEDs and wired the LEDs through small NPN transistors to control the transistor bases with arduino output signals.
Mind you, with resistors all the LEDs seem to exhibit roughly the same amount of brightness.
The power source is 3.4 V. Forward voltage of LEDs' is 3.2V. Forward current is 350 ma. I have done the calculation and used 1.2 Ohm resistors with LEDs. Do you think it will be fine?
That does sound low. You could have a thermal runaway, and it probably does not allow enough for variation in forward voltage between LEDs. Your mysterious 3.4V supply would also have to have an incredibly low impedance.
Try this test - mask off all but one LED and then toggle the rest of them on/off at a visible rate. See if there is a brightness variation in the visible one.
It would probably be much better to use 5V.
aarg:
That does sound low. You could have a thermal runaway, and it probably does not allow enough for variation in forward voltage between LEDs. Your mysterious 3.4V supply would also have to have an incredibly low impedance.
Try this test - mask off all but one LED and then toggle the rest of them on/off at a visible rate. See if there is a brightness variation in the visible one.
It would probably be much better to use 5V.
Hi. Thanks for feedback. For power supply I use a universal adapter with a dial on it. It is putting out 3.4 volts and up to 3 amps. Why would I use a higher volt power supply when the forward voltage of the led is 3.2?
I tested 4-5 volts briefly without a resistor and the LED was drawing too much current. I would have to use a resistor with more Ohm-age. Besides, now with my current setup all LEDs seem to draw 300 ma. Not bad for a 350 ma forward current rating. Why would I change to 5V?? I am just wondering if it will last. Thanks
arduinoware:
Hi. Thanks for feedback. For power supply I use a universal adapter with a dial on it. It is putting out 3.4 volts and up to 3 amps. Why would I use a higher volt power supply when the forward voltage of the led is 3.2?
I tested 4-5 volts briefly without a resistor and the LED was drawing too much current. I would have to use a resistor with more Ohm-age. Besides, now with my current setup all LEDs seem to draw 300 ma. Not bad for a 350 ma forward current rating. Why would I change to 5V?? I am just wondering if it will last. Thanks
I already answered your first question. The answer is because of variation in the LED forward drop between devices and also with temperature. The latter can cause "thermal runaway".
The second is just crazy. Of course it draws too much current! Look at the V/I curve of a diode to see why. I also answered this question - the answer is to gain thermal stability to eliminate the possibility of destructive thermal feedback, and to reduce the effect of LED forward voltage variation.
Lastly, if you're perfectly satisfied with things exactly the way they are, why are you asking for a second opinion?
Lastly, if you're perfectly satisfied with things exactly the way they are, why are you asking for a second opinion?
Or indeed a third opinion!
@arduinoware, please never use Photobucket again.
No disrespect. But I guess this is the forum with the most moaners in it. Every time I ask a question I get all these " Don't use photobucket", Don't quote", "Don't ask for opinions", "Don't post". I am not making it up. If you don't believe me, just have a look at the comments above. :)) Are you serious??
aarg:
I already answered your first question. The answer is because of variation in the LED forward drop between devices and also with temperature. The latter can cause "thermal runaway".
The second is just crazy. Of course it draws too much current! Look at the V/I curve of a diode to see why. I also answered this question - the answer is to gain thermal stability to eliminate the possibility of destructive thermal feedback, and to reduce the effect of LED forward voltage variation.
Lastly, if you're perfectly satisfied with things exactly the way they are, why are you asking for a second opinion?
Thanks. By the way, I am not PM-ing you. I am only using the "quote" feature. Thanks for explaning the thermal runaway. I guess you are referring to transistor.
Please excuse my lack of knowledge of electricity. But can you please explain how having a higher voltage power source can be more efficient when you have to deal with wasting power by dissipating power through resistors?
I am really not trying to argue. I am just trying to get my head arround it. Thanks
