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### Topic: Problems with voltage using a few leds (Read 7566 times)previous topic - next topic

#### leibniz81

##### Dec 10, 2013, 01:23 pm
Hello, I need help to complete my project. I´m going to explain my problems in my project:
I´m using 4 leds (2,4V) connected each led to each pin, so i´m using 4 pins. I´m doing that in order to switch on each led with a bit of delay among them, so I have an ascendent or descendent effect to switch on them. After this effect, all these leds keep on switched on. I´m feeding the arduino with 5 external volts.

Apart from these 4 leds i would like to switch on a set of another 4 leds (2,4V) simultaneously. But these new leds there will be switched on for 10 seconds. These leds are connected with a transistor in order to increase the current.

The problem I have is that, after having the initial 4 leds switched on I have not enough voltage to be able to see the set of 4 leds with a good brilliance. Then, the light that the leds provide is not very bright.
I realized measuring with a multimeter that the drop voltage drops up to 2.2 volt in the rest of the pins after switching on the initial 4 leds, so i don´t have enough voltage to handle the rest of the leds. How could i work out this problem?
I´ve tried using multiplexing and charlieplexing but it´s the same. So my problem is to be able to do the inicial effect with the leds using less pins or something like that. Am i doing any wrong?
Is there any possibility to maintain the voltage in the rest of the pins?

#### fungus

#1
##### Dec 10, 2013, 03:16 pm

I realized measuring with a multimeter that the drop voltage drops up to 2.2 volt in the rest of the pins after switching on the initial 4 leds, so i don´t have enough voltage to handle the rest of the leds. How could i work out this problem?
I´ve tried using multiplexing and charlieplexing but it´s the same. So my problem is to be able to do the inicial effect with the leds using less pins or something like that.

Put resistors in series with the LEDs.

150 Ohms.

Am i doing any wrong?

Yes, you will destroy your LEDs/Arduino/power supply of you keep on doing that.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### leibniz81

#2
##### Dec 10, 2013, 04:24 pm
Quote
Yes, you will destroy your LEDs/Arduino/power supply of you keep on doing that.

Sorry, but I don´t understand how you took this conclusion. Obviously I´m using resistors. But even so, that´s not the problem if you use resistor( I did it) the drop is the same and I will have also the same problems with the drop voltage.
Please put me right if i´m wrong.

#3
##### Dec 10, 2013, 04:33 pm
Do you have
pinMode (pinX, OUTPUT);
for each of the 8 pins driving an LED?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### leibniz81

#4
##### Dec 10, 2013, 07:05 pm
Thanks Crossroads for the reply, but yes I have all the leds defined as an output. May be my english is not very good and i couldn´t explain me properly. The similar example would be the next one:

You feed the arduino with 5 volts and define 8 pins as an output. Now if you measure the pins defined you will see 5 volts in each pin, but now you use 4 pins with a load in each pin. If i measure again in the free pins defined  before I see 2,2 Volts. I guess that it is normal, isn´t it? if you replace the load with leds, that´s my problem, and i haven´t enough voltage to add more leds in other pins.

#5
##### Dec 10, 2013, 08:13 pm
If the voltage is dropping that much, that usually indicates too much current is being drawn by the load. With LEDs, that would be from too small of a current limit resistor.

Or, your power supply is insufficient. When you see 2.2V at the LEDs, what is the measurement at the 5V pin on the power header?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### arduinodlb

#6
##### Dec 10, 2013, 08:16 pm

If i measure again in the free pins defined  before I see 2,2 Volts. I guess that it is normal, isn´t it?

No, that's not normal. It should still say 5V. It really sounds like you don't have a resistor in series with each Led, or the resistor you are using is much too small. If you have put a resistor in series with each led, what value resistors did you use?
Do not IM me. I will not respond. Ask questions in the forum.

#### nickgammon

#7
##### Dec 10, 2013, 08:24 pm
Quote

Now if you measure the pins defined you will see 5 volts in each pin, but now you use 4 pins with a load in each pin. If i measure again in the free pins defined  before I see 2,2 Volts. I guess that it is normal, isn´t it?

No.

You are allowed to send an absolute maximum of 40 mA out each pin, and preferably not more than 20 mA. Doing that will certainly not drop 5v to 2.2v, so there is something badly wrong. Please post your schematic, your code, and a link to the LEDs you are using.

You might also want to indicate how you are powering all this.
Please post technical questions on the forum, not by personal message. Thanks!

#### leibniz81

#8
##### Dec 11, 2013, 10:58 am
May be all of yours are right. I was using a 2 coin cell battery in series with 5.5 v and 600mAh. One of the problem could be that the value of my resistors were too small. They were 100 Ohms. I´ve changed them for 220 Ohm and I have less drop voltage.

With the leds switched off I measure 5,20 V on the power header.
With the leds switched on I measure 4,20 V on the power header.

Now the behavior it´s better, but even so I´m not very convinced of that.

#### TomGeorge

#9
##### Dec 11, 2013, 11:31 am
Hi, you can help us if you could post a copy  of your circuit, either using a cad program or a hand drawn diagram that you have photographed.
This way we can see how you have wired your LEDs and the batteries.

Tom.....
Everything runs on smoke, let the smoke out, it stops running....

#### fungus

#10
##### Dec 11, 2013, 12:09 pm

Quote
Yes, you will destroy your LEDs/Arduino/power supply of you keep on doing that.

Sorry, but I don´t understand how you took this conclusion.

You said the voltage is dropping on other pins.

Anything that causes voltage drop on other pins is doing something bad to the power supply.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### leibniz81

#11
##### Dec 11, 2013, 12:17 pmLast Edit: Dec 11, 2013, 12:19 pm by leibniz81 Reason: 1
This is my circuit, with 220 Ohms resistor in series in Pins 5,6,7 and 8 I see 3 volts in Pin 3 and 2, in the base of the transistor.

#### fungus

#12
##### Dec 11, 2013, 12:35 pmLast Edit: Dec 11, 2013, 12:36 pm by fungus Reason: 1

May be all of yours are right. I was using a 2 coin cell battery in series with 5.5 v and 600mAh.

There's your problem. Coin cells can only supply a few mA of current. 600mAh suggests a big one (CR2450?) but even a CR2450 can only supply about 25mA.

An Arduino+LEDs will draw far too many amps and the voltage will drop as a result.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### leibniz81

#13
##### Dec 11, 2013, 04:31 pm
Quote
Coin cells can only supply a few mA

Is this only a behavior of coin cells? What about AAA batteries?