Power LED Shield Instructions

Version 2

(For the Power LED Shield v1.6 documentation, click here or scroll down.)

Downloadable Documents

This page as a PDF

Application Examples (V2)

Power LED Shield Output Adjustment

Power_LED_Shield_Test

Specifications

  • Compatible with Arduino UNO, Duemilanove and others
  • 4 individually addressable channels
  • Any combination of colors
  • Dimming controlled with PWM, analog or both on each channel
  • Up to 39.6 Watts per channel; 158.4 Watts total output power
  • Up to 33V and 1200mA output per channel
  • Step-down (buck) drivers
  • 6 – 36 VDC input voltage @ 5 Amps Max
  • Capable of extremely low dimming values
  • Maximum brightness tuning per channel
  • Spring terminals allow easy changes
  • Stackable (estimated up to 8 shields can be stacked)
  • 4th standoff hole for more solid stacking of multiple shields
  • Requires no special code or libraries in your Arduino sketch.

Component Identification

In the following sections, components are referred to by their letter.

A) Pin-to-Channel Jumpers
B) PWM/Analog Jumpers
C) Maximum Brightness Adjusters
D) LED Spring Terminals
E) Power Screw Terminals

Quick Start

IMPORTANT: If the driver modules on your Power LED Shield are rated for higher current output than your LEDs can handle, you MUST set the output of the drivers before connecting your LEDs. See the “Advanced Setup” section later in this document for instructions on setting the driver output.

  1. Attach the shield to your Arduino.
  2. Set the Pin-to-Channel jumpers (A).
  3. Set the PWM/Analog jumpers (B).
  4. Connect your LEDs (D).
  5. Connect the power supply (E).
  6. Review all connections and jumpers.
  7. Turn on the power.
  8. Upload your sketch to your Arduino.
  9. Enjoy!

Introduction

The Power LED Shield is a circuit board for driving and controlling power LEDs (LEDs 1 Watt and higher). It fits directly onto the Arduino UNO/Duemilanove and other physically compatible Arduino boards and clones. The shield provides four individually dimmable power LED driver channels that are controlled by your Arduino sketch. Multiple Power LED Shields may be stacked onto the Arduino for many channels and/or higher capacity projects.

Arduino PWM Pin Assignment

Jumpers (A) allow the selection of which Arduino PWM pin (3, 5, 6, 9, 10 or 11) controls each channel on the Power LED Shield. Each channel can be assigned to any one of the Arduino PWM pins. A CMOS buffer on the Power LED Shield minimizes current drain on the Arduino pin. This allows the Arduino to drive any number of channels from a single pin without risk of overloading the pin.

LED Dimming Features

Jumpers (B) also allow the selection of dimming the LEDs directly with the PWM signal, converting the PWM to an analog voltage or mixing the PWM and analog signals. The different signals provide separate benefits and drawbacks.

PWM Dimming

Pulse Width Modulation (PWM) dimming works by turning the LEDs on and off very quickly to make them appear dimmer or brighter. The ratio of “off time” to “on time” determines the brightness of the LED. This high-speed flashing is undetectable by the human eye in most cases. However if the LED is moving or an object lit by the LED is moving, the observer sometimes sees a stroboscopic effect, which can be undesirable. (Think of how the tail lights of some recent model cars look when your eye darts around the road.) LED manufacturers recommend using PWM to dim the LEDs if the project is sensitive to color shift. This is because LEDs change color slightly as the current through them changes. PWM allows dimming with the least amount of color shift in the LEDs because during the time the LEDs are on, they are always at the same current level.

Analog Dimming

Analog dimming converts the PWM to a voltage level which changes the current flow through the LEDs. This eliminates the high-speed flashing caused by PWM. Analog dimming is more suitable for projects involving motion, and other specific situations. But with analog dimming, the LEDs may color shift as the brightness changes.

Mixing Analog and PWM Dimming

Usually, choosing either PWM or analog dimming is sufficient for a project. However, if your project requires very low dimming values, you can mix PWM and analog dimming. When both signals are mixed, the analog dimming is imposed upon the PWM dimming and their effects are additive.

Maximum Brightness Adjustment

For further flexibility, each channel has a Maximum Brightness adjustment (C). These work in conjunction with the dimming control to define the maximum LED brightness in cases where the driver module can deliver more current than is desirable for the LEDs. It also allows the user to fine-tune the brightness of each channel for color balance between channels.

Basic Setup

IMPORTANT: If the driver modules on your Power LED Shield are rated for higher current output than your LEDs can handle, you MUST set the output of the drivers before connecting your LEDs. See the “Advanced Setup” section later in this document for instructions on setting the driver output.

Setting the Pin-to-Channel Jumpers

Pin-to-Channel jumpers CH1-CH4 (A) determine which of the Arduino PWM pins (3, 5, 6, 9, 10 or 11) will be used to drive each channel on the Power LED Shield. You may drive any channel from any pin and multiple channels may be driven from the same pin. NEVER select more than one pin on a channel, or you will damage your Arduino. If you do not select a pin, the LEDs on that channel will remain off.

The Power LED Shield is shipped with the Pin-to-Channel jumpers set as follows: Channel 1: Pin 3; Channel 2: Pin 9; Channel 3: Pin 10; Channel 4: Pin 11

To assign an Arduino pin to a channel on the Power LED Shield, place the shunt onto the numbered jumper position for that pin.

Setting the PWM/Analog Jumpers

PWM/Analog Jumpers JP1-JP4 (B) determine whether each channel is dimmed with PWM, analog or both. You may choose one or both dimming modes on each channel.

To select the PWM dimming mode on a channel, place the shunt in the ‘On’ position of the ‘P’ jumpers. To select the Analog dimming mode on a channel, place the shunt in the ‘On’ position of the ‘A’ jumpers. If both shunts are placed in the ‘On’ position, both dimming modes will be used for that channel. If a channel does not have at least one shunt in the ‘On’ position, that channel will remain off.

Connecting the LEDs

Spring terminals (D) allow quick and easy connection of the LED wires. The spring terminals can accept wire sizes 24 AWG to 20 AWG.

There are 4 LED output connections; one for each driver channel. Each output is completely separate from all other outputs. NONE OF THE CONNECTIONS ARE COMMON. Do not use common cathode or common anode LED arrays with the Power LED Shield. And do not connect any of the output “-” (negative) connections to ground. Each output can drive one or more LEDs in series, parallel and series-parallel configurations.

To connect your LED wire leads, strip approximately 3/8” (9mm) of insulation from the wire and insert it completely into the bottom hole of the spring terminal. For best results, tin the wire ends before inserting them. Make sure there are no bare strands of wire exposed outside the wire hole.

To release a wire from its spring terminal, insert a very small (1.5-2mm) flat screwdriver into the top hole and gently push until the wire is released, then remove the wire.

Connecting Power

Screw terminals (E) are provided for easy attachment of the power input wires. Pay close attention to polarity when connecting power. Positive (+) and negative (-) symbols are screened onto the board for clarity.

Fine-Tuning the LED Maximum Brightness

Maximum Brightness Adjuster trim-pots R1-R4 (C) change the maximum current through the LEDs, relative to the driver module’s output specification. They allow you to fine-tune the LED brightness for balance between channels by limiting the output current of the driver module on the corresponding channel.

To reduce the LED maximum brightness, turn the trim-pot counter-clockwise. To increase the brightness, turn the trim-pots clockwise.

When the trim-pot has been turned fully counter-clockwise, the LEDs on that channel will be completely off. Turn the trim-pot fully clockwise for maximum output current on that channel.

The LEDs will transition from off to about 50mA at minimum brightness and will reach full brightness about 1-2 turns before the trim-pot’s maximum travel. At both ends of travel, the internal clutch disengages to allow overturn to prevent harm to the trim-pots.

Advanced Setup

IMPORTANT: If the driver modules on your Power LED Shield are rated for higher current output than your LEDs can handle, you must follow the instructions below before connecting your LEDs.

Summary

This procedure involves connecting a dummy load and an ammeter to each channel and adjusting the Maximum Brightness adjusters until the desired output is reached. Repeat for all four channels.

Tools required

  • Flat tip micro screwdriver (1.5-2 mm)
  • Ammeter with a range of at least 1.5 A
  • 4 Ohm – 8 Ohm/20 Watt power resistor
  • Alligator clip jumpers and other wire pieces for temporary connections
  • 12V DC power supply
  • Arduino board, ready to be connected to your computer
  • The Power LED Shield Output Adjustment sketch
  • The Power LED Shield Test sketch

Set the Driver Output

  1. Attach the shield to your Arduino.
  2. Set all Pin-to-Channel jumpers (A) to pin 3.
  3. Set all PWM/Analog jumpers (B) to Analog only.
  4. Connect the power resistor and ammeter to one channel (D).
  5. Connect power to the Power LED Shield (E).
  6. Connect your Arduino to your computer.
  7. Upload the ‘Power LED Shield Output Adjustment‘ sketch to your Arduino.
  8. Using the Maximum Brightness Adjuster (C), set the output of the LED driver.
  9. Disconnect the power.
  10. Repeat for all channels.
  11. Connect your LEDs.
  12. Upload the ‘Power_LED_Shield_Test‘ sketch to your Arduino and let it run a few minutes.
  13. Upload your sketch to your Arduino and ENJOY!

Installing Driver Modules

If you bought your Power LED Shield without driver modules, and will be purchasing your modules separately, there are some things to keep in mind.

Mix and Match

You may install any number or combination of driver sizes you like. To avoid damaging your LEDs, you should purchase driver modules rated the same or lower current output than your LEDs can handle.

Important Soldering Note

Some of the solder pads have a small group of extra holes around them. Be sure to fill the extra holes with solder. This is to assure good electrical conductivity to the power input pins of the driver modules.

Using the Power LED Shield

Tips, Cautions and Built-In Protections

The Power LED Shield was built to be a robust circuit that can withstand some level of adversity. However, no circuit can handle all possible misconfigurations or errors on the part of the builder.

Always pay close attention to assure proper polarity of your connections. In all cases, improper polarity will damage the Power LED Shield, your LEDs, and/or your Arduino board.

Be careful to never allow metal to come in contact with the bottom side of the Power LED Shield while power is applied. This could cause hazardous conditions or short circuits in the board which may damage the Power LED Shield or other components. The shield was designed to properly clear all metal components on the Arduino board.

The output connections of the RECOM RCD-24 line of LED drivers used on the Power LED Shield can withstand indefinite open and short circuit conditions. However, short circuit conditions should always be avoided as a matter of proper electrical practice. Please see the RECOM data sheet for more information on the RCD-24 driver module. (http://www.recom-power.com/pdf/Lightline/RCD-24.pdf)

Heat and Thermal Management

It is important to keep your Power LED Shield cool during operation. This is especially true if you have multiple Power LED Shields stacked together. Usually, assuring free air flow around the shield will result in sufficient cooling. However, if the shield is being used in a closed space or near a source of heat, you should consider installing a fan to keep the shield cool.

If you are stacking multiple Power LED Shields, you should secure them together with one or more Shield Standoff kits, available at http://www.chestersgarage.com. The standoffs will separate the shields about 1 mm further than without the standoffs, allowing better cooling of the LED driver modules.

Known Anomalies

When the Power LED Shield is connected to an Arduino that has power, but the Power LED Shield is not powered, the power indicator LED on the shield may glow or flicker. This is normal and will not hurt any circuits.

Software Control

The Power LED Shield does not require special libraries or plug-ins in order to be fully utilized. It is simply controlled by either the digital state or the PWM signal available on Arduino pins 3, 5, 6, 9, 10 or 11.

To set or change the LED brightness issue an ‘analogWrite()’ command to the correct pin in your Arduino sketch. A value of 0 (zero) shuts off the LEDs completely and a value of 255 sets full brightness.


Version 1

Power LED Shield 1

Introduction

The Power LED Shield is a printed circuit board that fits directly onto the Arduino Duemilanove and other physically compatible Arduino boards and clones.  It provides four Pulse Width Modulation (PWM) dimmable, optically isolated power LED driver channels.  The board was designed around LED Dynamics’ BuckPuck™ and BoostPuck™ power LED driver modules.

Each channel can be addressed by any one of pins 3, 9, 10 or 11 on the Arduino, which is selectable on jumpers CH1-CH4 on the shield.  The Arduino pin drives a CMOS buffer to minimize current drain on the pin.  The buffer drives an opto-isolator input, which in turn controls the dimmer pin on the driver module.  Opto-isolation protects the driving logic from voltage differences present in the driver modules.

For further flexibility, each channel also has a current-limiting trimpot.  The trimpot works in conjunction with the PWM control to define the maximum current through the LED in cases where the driver module can deliver more current than is desirable for the LEDs.  This allows the user to fine-tune the brightness of each LED for color balance or any other need.  The trimpots can be omitted if current limiting is not necessary.

The shield has its own power input that accepts between +6V and +32V DC up to 4.5A.  The 7805 three-pin regulator powers the Arduino from the shield.

The shield can drive as few as one LED on one channel, or up to 18 1W LEDs on each channel for a total of 72 LEDs on a single shield!  That’s 72 Watts of high-efficiency light!

Choosing Driver Modules

You may use any combination of the following driver modules.

Compatible Driver Modules

Whether to use buck or boost modules is determined by how you connect your LEDs compared to the voltage of your power supply.  For example, if you have 5 LEDs at 3.6 volts each, all connected in series, then the driver module will have to output 18 volts to light the LEDs.  You will need a boost driver module if your power supply provides less than 16 volts or a buck driver module if your power supply provides more than 20 volts.  You will need to change your LED configuration if your power supply provides between 16 and 20 volts because the driver modules require at least 2 volts difference between the input and output voltage.

NOTE: While any of the BuckPuck modules above will work, it makes little sense to use anything other than the 1000mA modules.  They are all about the same price and the Power LED Shield allows you to adjust the output of the BuckPucks for your needs.  Using a lower value module will only serve to limit the flexibility of the Power LED Shield.

The overall input and output requirements/capabilities of the Power LED Shield will vary based on your selection of driver modules.

Building the Kit

Unpack the kit and organize the parts in front of you for easy access.  Assure all parts are included and that you have obtained the correct LuxDrive modules for your needs.

Pay close attention to the IC orientation.  See below for a picture of what it should look like.  The silkscreen on the circuit board is a bit misleading because the text is upside down and I have had some customers install the ICs backward as a result.

For easy assembly, solder the parts into the circuit board in the following order:

  1. IC sockets
  2. Resistor network and small ceramic capacitor
  3. All jumper pins
  4. Stacking headers
  5. Screw terminals
  6. Trimpots
  7. LuxDrive modules
  8. Large capacitors
  9. 5v regulator

Once Everything is soldered into the circuit board, insert the ICs into their sockets and screw the heat-sink onto the 5v regulator.  If you are stacking multiple Power LED Shields, screw the heat-sinks on sideways, short end toward the power terminals so they do not interfere with each other.  It’s OK for the heat-sinks to touch each other.  They are electrically common.  Don’t forget to use thermal paste between the heat-sink and the 5v regulator!

Initial Power-On

The Power LED Shield can be powered up without being connected to an Arduino.  This allows you to test your build without risking damage to your Arduino.

After building your kit or before attaching LEDs for the first time, perform the following initial power on sequence:

  1. Do not attach the shield to an Arduino
  2. Assure all power is turned off or disconnected
  3. Disconnect all LEDs from the shield
  4. Set all channel jumpers to pin 3
  5. Close jumpers J1 and J2
  6. Run a wire from pin 3 to the 5v pin
  7. Turn all trimpots all the way counter-clockwise until you hear the faint click
  8. Connect the anode (+) of an LED to the “+” screw terminal of the first channel
  9. Connect the negative (black) lead of an ammeter to the “-” screw terminal of the first channel
  10. Connect the cathode (-) of the LED to the positive (red) lead of the ammeter
  11. Turn on the power
  12. Adjust the trimpot on the first channel until the desired current level is reached
  13. Turn off the power
  14. Disconnect the ammeter and LED
  15. Repeat steps 8 through 14 for the remaining channels
  16. Remove the wire between pin 3 and the 5v pin
  17. Connect your LEDs

Your Power LED Shield is now ready to be attached to your Arduino!

Setup and Adjustment

Jumpers

J1 and J2 must be open when you are powering the Arduino from the USB port, DC jack or other power source.   Place jumpers on J1 and J2 to power the Arduino from the +5V regulator on the Power LED Shield.  Always open or close BOTH of J1 and J2 for proper operation.

CH1-CH4 determine which of pins 3, 9, 10 or 11 will be used to drive each channel on the Power LED Shield.  Place a jumper on the outer-most pair to use pin 3 for that channel, the next pair inward for pin 9 and so on.  See Power LED Shield v1.6 diagram (PDF) below.  You may drive any channel from any pin and multiple channels may be driven from the same pin.  DO NOT jumper more than one pair on each channel or you may damage your Arduino.

LED Maximum Current Adjustment

Multi-turn trimpots R1-R4 set the maximum brightness of the LEDs by limiting the output current of the driver module on the corresponding channel.  With the trimpot turned fully counter-clockwise, the LED for that channel will be completely off.  Turn the trimpot fully clockwise for maximum output current and full LED brightness on that channel.  The LED will transition from off to about 50mA at minimum brightness and will reach full brightness about 1-2 turns before the trimpot’s maximum travel.  At both ends of travel, the trimpots will make a very faint click as the clutch disengages to allow overturn.  This is normal and won’t harm the trimpots.

If you purchased a built Power LED Shield, the trimpots have been turned fully counter-clockwise.  This sets the LED output to “off” for safety.  You need to adjust the output for your needs using the Initial Power-On instructions above.

If you purchased a kit, you should turn all the trimpots fully counter-clockwise and follow the Initial Power-On instructions above.

If your driver modules are capable of more current than your LEDs can tolerate, you must adjust the output current to a safe level before connecting the LEDs for the first time.  Turn the trimpots all the way counter-clockwise and follow the Initial Power-On instructions above.

LEDs

When you apply power to the shield without it connected to an Arduino, the LEDs may flicker erratically.  This is normal and the LEDs can be stabilized by setting all channel jumpers to pin 3 and running a wire from pin 3 to the 5v pin.

There are 4 LED output connections; one for each driver channel.  Each output is completely separate from all other outputs.  NONE OF THE CONNECTIONS ARE COMMON.  Do not use common cathode or common anode LED arrays with the Power LED Shield.  And do not connect any of the output “-” (negative) connections to ground.  Each output can drive one or more LEDs in series, parallel and series-parallel configurations.

Connect the negative or cathode connection of the LED to the “-” screw terminal of one channel.  Connect the positive or anode connection of the LED to the “+” screw terminal of the same channel.  Do this for each channel.  If you wish to run more than one LED per channel (very common), you will need to connect your LEDs to each other in series or parallel before connecting them to the shield.  See Power LED Shield Application Examples below for more information.

Power

The shield is powered through the pair of screw terminals closest to the 4 large capacitors.  Pay attention to the polarity when connecting your power supply.  Positive (+) and negative (-) signs are printed on the PC board for clarification.

The voltage input requirements of the shield should be taken as the most restrictive of the driver modules selected.  Calculate the total current draw of the shield from the total wattage of the LEDs, divided by the power supply voltage, plus 25-40% for inefficiency and overhead.

Software Control

The shield is controlled by either the digital state or the PWM signal available on pins 3, 9, 10 and 11.  Changing the LED brightness is simply a matter of issuing an ‘analogWrite()’ command to the correct pin in your sketch.  A value of 0 (zero) shuts off the LED completely and a value of 255 sets full brightness.

Additional Resources

Power LED Shield v1.6 diagram (PDF)

Power LED Shield demo sketch

Power LED Shield Application Examples

Power LED Shield Printed Instructions

Power LED Shield Kit Printed Instructions

IC Orientation

Power LED Shield Example

Power LED Shield Bottom

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