# Low Current...!!

I have a project which runs an LED. Unfortunately, I found out that the current passing through the LED was not sufficient to make the LED glow brightly.

Is there any way that I can enhance current to brighten up the LED...??

What kind of LED? How are you driving it?

There are 50mW LEDs and there are 150W LED panels, and multiple driving schemes, each applicable to LEDs within a different range of sizes.

A schematic of your project (hand drawn is ok) would definitely help to clarify some open questions.

Lower series resistance will give you more current ([u]Ohm's Law[/u]).

Here's an [u]online LED resistor calculator[/u]. (You'll need to know the voltage & current ratings for the LED.)

But, don't exceed the current rating for the LED or the driver circuit.

SagarDev:
I have a project which runs an LED. Unfortunately, I found out that the current passing through the LED was not sufficient to make the LED glow brightly.

Is there any way that I can enhance current to brighten up the LED...??

Well not much to say, you give no concrete details. Hint: give full details with values and part numbers / datasheets.

LEDs have a threshold voltage. e.g. 1.8volt for a red smd LED or 3.3volt for a 5mm blue or white LED.
Below that threshold nothing much is happening, independent of the value of the current limiting resistor.

So you need at least the Vf (working voltage) of the LED, plus a bit more for the CL resistor.

If you know the supply voltage, and Vf of the LED, then you can calculate the voltage across the CL resistor.
And work out the current for a certain resistor value, or calculate the resistor for the current you want.
Leo..

And keep in mind what the max for the Arduino is. For an Uno it's max 40mA per port and 200mA total.

.. and LED's have "+" and "-" (anode, cathode) which shouldn't be mixed up to get a glow...

This is a circuit of a touch sensor. When touched the LED glows at a medium brightness. It glows way brighter when I connect a 1M resistor instead of the touch terminals.

Note: I used a 220 O resistor instead of the 470 O

septillion:
And keep in mind what the max for the Arduino is. For an Uno it's max 40mA per port and 200mA total.

Those are Absolute Maximum Ratings. The datasheet has this nice helpful note right next to it:

Read that a couple times to make sure you get it.

That "40 mA" crap needs to DIE. All the graphs in the "Pin Driver Strength" section stop at 20 mA, so consider that to be the recommended operating limit.

Sounds to

SagarDev:
This is a circuit of a touch sensor. When touched the LED glows at a medium brightness. It glows way brighter when I connect a 1M resistor instead of the touch terminals.

Note: I used a 220 O resistor instead of the 470 O

measuring across skin is usually >1 megaohm.

I think the transistor just doesn't have enough gain to make the LED turn on as bright as you want....

What's the collector-emitter voltage on the BC547 when you're touching the leads? if it's too high it means the transistor isn't going into saturation.

Can anyone please summarize what I have to do?

Wet your fingers before touching the probe for better conductivity and brightness.
Or change the NPN to a logic gate N-channel MOSFET with low Rds, such as AOI514.
That takes very little current to turn on, just voltage. May have to add a 1M ohm resistor from gate to Gnd to let it bleed off gate voltage to turn off.
50 cents at Digikey.com

Use a transistor with more gain?
Or maybe a mosfet, though you'd need a high value indeed for the pulldown to avoid interfering with operation.

Your transistor is not going into saturation, not even close, so the current that a BJT will pass depends on the current flowing through the base, and the gain of the transistor. Using a transistor with more gain is almost certainly easier than trying to get more current to flow through the skin of the person touching it.

Alternately switch to a different touch sensing mechanism entirely - you can get more reliable and consistent results with a commercial touch sensing IC. I even sell some on a breakout board

If you have a spare transistor, try this:

From new link (improved version, can use 9V battery and 470Ω for second resistor)

If you have a spare transistor, try this:

If that doesn't work nothing will.

Thanks for the schematic guys. It is working well and good...

Thanks for the schematic guys. It is working well and good..

.

Whatever you do, don't short the base of the first transistor to 5V or you'll destroy both transistors.

... or just add a 1K resistor in series.