16 Channel ULN2XXX Darlington Transistor Array Breakout Board




Introduction: 16 Channel ULN2XXX Darlington Transistor Array Breakout Board

About: electro-mechanical goodness.

The Lekramek ULN-BOB V2.0 is the Swiss Army knife of darlington transistor array breakout boards.

Up to 16 channels of NPN darlington transistor outputs available.

Thin profile allows it to be slipped into cramped enclosures or panels. It can be sewn or placed onto clothing, without things sticking up, or into the wearer.

Double-row output profile allows a 20-pin ribbon cable to be connected for convenient cable routing, and flexible applications such as along actuators, or through sleeves of clothing. Simple female end jumpers can still be used to connect to things like breadboards.

Another unique aspect of the Lektramek ULN-BOB V2.0 is the addition of the AUX1 and AUX2 inputs on JP3. This screw terminal connection allows additional voltages or signals to be injected into the ribbon cable connection, or can be used to effectively turn the ULN-BOB V2.0 into two separate 8 channel darlington transistor array breakout boards, each with their own supply voltage.

It is not:

It is not a DAC (digital to analog converter). The outputs go to either to the supply voltage or 0V. Nothing in between.

It is not meant for total current above 2A. The ICs are not heatsinked, and would be hot to the touch!

It is good for:

This board is great for driving a couple 12V, high-current motors from an Arduino or Raspberry Pi. Or, one big honkin' 24V 2A motor. This would be accomplished by tying all of the inputs together, and all of the outputs together.

This board is also great for driving small-signal LEDs, or connecting microcontroller pins from larger voltage outputs, like in a PLC.

The inputs or supply voltage can be pulsed, allowing for PWM.


The original need for this board came from my work with PLC's. I needed to be able to test the 24V outputs of a Unitronics V570. I had set up an Arduino Mega to monitor the the system, but need to level-shift the PLC outputs.

I designed the first ULN-BOB to convert the 24V to 5V signals, safe enough for the Arduino Mega.

Step 1: Description of Designators

Description of all of the designators:

JP1. The control voltage comes in from this 18 pin right angle row-header. IN1 - IN16 go to U1 and U2, while V+ and V- connect to the main voltage terminals at JP2.

JP2. The outputs after U1 and U2, can be directly connected, or current-limited by resistors. V+, V-, AUX1, AUX2 can be picked up here as well.

JP3. The V+ is the positive side of the voltage, and V- is the negative. This set of screw terminals is where the main voltage comes in. It is hardwired to the U1 supply pin. It also connects to V+ and V- on JP1, and JP2

JP4. AUX1 and AUX2 can be used to spilt the ULN-BOB V2.0 into 8 channels of two voltage levels, i.e. U1 has a 12V supply from V+ and V-, and U2 could have a 5V supply from AUX1 (positive voltage) and AUX2 (Ground). Or, simply use JP4 as a way to inject signal(s) into the ribbon cable at JP2. AUX2 can be a separate ground, or two other voltages can be used referenced to V- on JP3.

U1, U2. These are for ULN23XXX IC's. Please note the small circle in the lower-left of the rectangular outline. This designates pin 1.

Step 2: Solder the Jumper Pads on Top Side of Board

The small pads and holes between U1, U2 and JP2 provide a convenient, yet configurable scheme to limit the amount of current at the output of JP2.

Some devices, such as LED's and microcontroller inputs, will consume as much current as possible, and will burn themselves out!

By inserting resistors into the holes (See Step 5), the ULN2XXX can safely drive LED's and connect to microcontroller input pins.

  • If full current is desired, simple create solder bridges across the pads.
  • If connecting to LED's or GPIO pins, skip to Step 5. It will be much easier to wait to solder the resistors last!

Step 3: Solder the Jumper Pads on the Bottom Side of the Board

To connect the main voltage from JP3 to all 16 channels, solder the pads together as show in the photo.

Be careful not to cause and solder bridges on the neighboring vias.

Step 4: Solder the JP1, JP2, JP3, and JP4 Connectors.

###EDIT### Please note that JP2 is installed BACKWARDS in the photo! The slot for the 20 Pin Ribbon Cable should be facing JP1. (sorry...)

JP3 and JP4 have the open slots facing out from the board.

Step 5: OPTIONAL (If Installing Resistors)

This is the optional step if you are using the board to control LEDs, and would like to use the onboard resistor holes.

Common LED current-limiting values range from 220 to 330 ohms.

The resistors can be pulled flush, or inserted at an angle.

Bend the leads away to hold the resistors in place whole soldering.

Clip the excess leads after soldering.

If using with clothing, try clipping the resistor and connectors leads very close to the boards, to avoid pokes and snags.

Step 6: Connect Ribbon Cable or Female Jumpers to JP2. Female Jumpers to JP1.

Link to Female to Male Jumpers: http://amzn.to/2qYrDN0

Link to 20 Pin Ribbon Cable: http://amzn.to/2rX1jlN

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    2 Discussions


    3 years ago

    Great. If using in clothing just stick a piece of duct tape across teh back?


    3 years ago

    That looks good, good instructable :)