PicoBuck Hookup Guide V12 Datasheet by SparkFun Electronics

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PicoBuck Hookup Gu
PicoBuck Hookup Guide V12
Introduction
Please note that this tutorial is for the newest version of the PicoBuck, V12.
If you have an older version of the PicoBuck, please refer to this tutorial.
Developed in collaboration with Ethan Zonca of protofusion, the PicoBuck is
a small-size, triple-output, constant current LED driver. By default, each
channel is driven at 330mA; that current can be reduced by either
presenting an analog voltage or a PWM signal to the board. Version 12 of
the board adds a solderable jumper that can be closed to increase the
maximum current to 660mA. It also increased the voltage rating on the
various components on the board, allowing the board to be used up to the
full 36V rating of the AL8805 part.
Suggested Reading
Here are some topics you should know before using the PicoBuck. Have a
look if you need more information.
•LEDs
•Resistors
• Voltage
• Current
Electric Power
Pulse Width Modulation
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PicoBuck Overvie
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Since the PicoBuck is a constant current driver, the current drawn from the
supply will drop as supply voltage rises. At 12V, the PicoBuck drives the
three LEDs on our Rebel Triple Play board at 350mA per LED while
drawing less than 350mA total from the power supply.
Three signal inputs are provided for dimming control. You can use the
PWM signal from an Arduino or your favorite microcontroller to dim each
channel individually, or you can tie them all to the same PWM for
simultaneous dimming. A separate ground pin (labeled GND) is provided to
reference against the controlling module for accuracy. The pin spacing for
the two pairs of pins is 0.1", but the two pairs are slightly 0.2" apart, to allow
for a 2.54mm pitch screw terminal pair to be used, or for a five-position
standard 0.1" header with the middle pin removed. Dimming can be done
by an analog voltage (20%-100% of max current by varying voltage
from .5V-2.5V) or by PWM (so long as PWM minimum voltage is less
than .4V and maximum voltage is more than 2.4V) for a full 0-100% range.
Signal Inputs
The power supply pads are sized for 3.5mm screw terminals, as are the
output pads. Each output is independent from the other two.
Power Input
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Output Pads
Note: The PicoBuck cannot be used to drive a common anode or
common cathode LED or LED string, and the individual channel +/-
pads must not be connected to one another.
A small jumper is provided for each channel to allow you to increase the
drive strength from 330mA to 660mA. More information on this can be
found below.
Solder Jumpers
Two mounting holes for 4-40 or M3 screws are provided on either side of
the board. They are perforated so they can be easily snapped off with a pair
of pliers, if a smaller footprint is desired.
Mounting Holes
It is possible to increase the maximum current of the PicoBuck board up to
1A per channel; to do so, replace the three current sense resistors with
smaller values. To calculate the new value for the resistor, use this formula:
I = 0.1 / R
LED set
Thus, for a 1A current, you’d want a 0.1 resistor. Don’t forget to be wary of
current ratings. At 1A, the sense resistor will be dissipating 1/10W, so you
probably want a resistor of at least 1/8W rating. The package is a standard
0805.
Current Set Resistors
Closing the Current Setting Jumpers
As you can see from the image above, the solder jumper doesn’t need to
be closed particularly neatly. All of the pads in its vicinity are connected to it
anyway, so if you glob a little extra solder on, it’s no big deal. Just be
careful not to actually short the resistors, as in the rightmost circuit!
Dimming with a Microcontroller
As mentioned earlier, the PicoBuck’s three channels can be individually
dimmed by either varying the input voltage of the channel from 0-2.5V or
using a PWM signal. The PWM signal from an Arduino board is perfectly
suited for this.
Connecting one LED per channel
Here’s a diagram showing how to connect the PicoBuck to an Arduino.
Note: Despite using an external supply for the PicoBuck, the grounds
of the two boards must be connected! If the power supply is 12V or
less, the Arduino can be powered from it as well, but do not attempt to
power the PicoBuck from the Arduino!
Also note that each channel must be independently connected to the + and
- connections of the LED it is to drive! Do not connect the + or -
connections of any two channels together.
More than one LED per channe
l
Multiple LEDs can be connected in series, as shown, and the supply
voltage should be at least 2-3V higher than the sum of the forward voltages
of the LEDs.
Multiple LEDs can be connected per channel; they should be connected in
series, as shown above, and the power supply voltage must be at least
1-2V higher that the sum of the forward voltages of the LEDs.
For instance, our blue 3W LEDs have a forward voltage of 3.2V to 3.8V. To
be on the safe side, use the highest voltage in the range. If you want to
connect four of them, you’d need a power supply of ~17V or greater (3.8V +
3.8V + 3.8V + 3.8V = 15.2V; add 2V of “head room”).
Since 17V is greater than the Arduino can tolerate on its input, we have to
provide an external supply for the Arduino as well. This can be the standard
5V USB supply.
It’s perfectly acceptable to mix colors either between channels or on one
channel, so long as all of the LEDs can handle the current (330mA or
660mA, depending on the jumper setting). Just make sure that the power
supply voltage is high enough to handle the sum voltages of the highest
voltage string. There is also no requirement that the three strings of LEDs
have the same forward voltage of LEDs across them; you could have one
white LED on channel 1, two red LEDs on channel 2, and four green LEDs
on channel 3.
Code example
Code for controlling this device is trivial; simply use the analogWrite()
function to adjust the brightness via PWM.
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PicoBuck_Example (https://codebender.cc/sketch:180514?
referrer=sparkfun) by sparkfun (https://codebender.cc/user/sparkfun?
referrer=sparkfun)
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[ Edit
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/*
*
* PicoBuck Breakout Example
* Mike Hord @ SparkFun Electronics
* Nov 5 2015
*
* A simple example showing how to control a PicoBuck with
*
* License: http://opensource.org/licenses/MIT
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF A
N
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. I
N
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, D
A
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OT
H
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* THE SOFTWARE.
*/
const int CHL_1 = 3;
const int CHL_2 = 5;
const int CHL_3 = 6;
void setup()
{
pinMode(CHL_1, OUTPUT);
pinMode(CHL_2, OUTPUT);
pinMode(CHL_3, OUTPUT);
}
void loop()
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Resources and Going Further
Thanks for reading. Below are all the documents and links you’ll need to
learn even more about the PicoBuck.
PicoBuck Schematic
PicoBuck GitHub Repository
AL8805W5 Datasheet
Protofusion Page
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