Everything You Ever Wanted To Know About The ULN2003

May 25, 2024 by Donald Papp 27 Comments

The ULN2003 IC is an extremely versatile part, and with the help of [Hulk]’s deep dive, you might just get some new ideas about how to use this part in your own projects.

Each of the seven outputs works like this simplified diagram.

Inside the ULN2003 you’ll find seven high-voltage and high-current NPN Darlington pairs capable of switching inductive loads. But like most such devices there are a variety of roles it can fill. The part can be used to drive relays or motors (either brushed or stepper), it can drive LED lighting, or simply act as a signal buffer. [Hulk] provides some great examples, so be sure to check it out if you’re curious.

Each of the Darlington pairs (which act as single NPN transistors) is configured as open collector, and the usual way this is used is to switch some kind of load to ground. Since the inputs can be driven directly from 5 V digital logic, this part allows something like a microcontroller to drive a high current (or high voltage, or both) device it wouldn’t normally be able to interface with.

While the circuitry to implement each of the transistor arrays isn’t particularly complex and can be easily built by hand, a part like this is a real space saver due to how it packs everything needed in a handy package. Each output can handle 500 mA, but this can be increased by connecting in parallel.

There’s a video (embedded below) which steps through everything you’d like to know about the ULN2003. Should you find yourself wanting a much, much closer look at the inner secrets of this chip, how about a gander at the decapped die?

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No Need For Speed With This Arduino-Based Inkjet Printer

June 13, 2020 by Dan Maloney 17 Comments

When it comes to computers, it seems like the only thing that matters is speed. The more the better, in general, and the same applies to peripherals. We want the fastest network adapters, the fastest video card, and the fastest printer. So why in the world would anyone intentionally build a really slow inkjet printer? For art, of course.

At least that’s the story [HomoFaciens] tells us in the video below. His efforts are in support of a friend’s art project, which seeks to print slowly but continuously on a roll of paper. [HomoFaciens]’s printer is based on an H-P C6602 inkjet cartridge, one of those high-priced consumables that make buying a new printer more attractive than replacing them once depleted. After figuring out how to drive the printhead — 5 to 6 μs pulses of 18 volts through a ULN2803 Darlington array driver chip seemed to do the trick — he mounted everything to the gantry of an old 3D printer. It’s interesting to watch the images slowly being built up — something that printers usually hide from prying eyes — and to see how the DPI count of the printer can be increased by interlacing each printed line.

Near the end of the video, we get a glimpse of his “tattoo gun printer”, which reminded us of all the other cool things he’s done over the years. From a CNC machine made from paperclips and cardboard to an encoder made from a wheel of resistors, [HomoFaciens] has some interesting designs that you really should check out.

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Sidney Darlington

October 23, 2018 by Dan Maloney 32 Comments

In a field where components and systems are often known by sterile strings of characters that manufacturers assign or by cutesy names that are clearly products of the marketing department and their focus groups, having your name attached to an innovation is rare. Rarer still is the case where the mere mention of an otherwise obscure inventor’s name brings up a complete schematic in the listener’s mind.

Given how rarely such an honor is bestowed, we’d be forgiven to think that Sidney Darlington’s only contribution to electronics is the paired transistor he invented in the 1950s that bears his name to this day. His long career yielded so much more, from network synthesis theory to rocket guidance systems that would eventually take us to the Moon. The irony is that the Darlington pair that made his name known to generations of engineers and hobbyists was almost an afterthought, developed after a weekend of tinkering.

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Animating An LED Matrix Without A Microcontroller

February 9, 2011 by Mike Szczys 20 Comments

[Konstantin] had some extra 27C256 EPROMS lying around and decided to use them to animate an 8×8 LED matrix. He’s not only using them to store data, but driving the display with them as well. The chip holds 32 kilobytes of data which equates to 4096 frames of animation. A 32 kHz clock circuit works with some ripple counters to scroll through each byte of stored data, turning on the columns while sinking the proper row. Of course current protection is a must so there is a ULN2308A darlington driver and some 2N2907 transistors at work, but you won’t find a programmable microcontroller. Neat!

Yep, you read that right. The picture above shows an EPROM chip that requires a UV light source to erase the data.

[Thanks Kopfkopfkopfaffe]

Simple Touch Sensor And Other Lessons

February 3, 2011 by Caleb Kraft 21 Comments

[HankDavis] sent along this link to a video showing a tutorial on how to make touch sensors using a “darlington pair”. In the video we are taken through the idea and how we’re going to construct it. [Thad]explains in detail how this works in simple terms and illustrates it clearly. Unfortunately they don’t show an actual constructed system, but this is so simple you could toss it together quickly and see for yourself. This is a great lesson on how to get a simple touch sensor into your projects. This video appears to be one of a series of class visuals, and you can find several others on youtube under this account.

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Beginner Concepts: LPT Instead Of UC

March 27, 2010 by Mike Szczys 28 Comments

We see it all the time, a post based on an Arduino board with multiple comments calling it overkill. How exactly should you control your homemade peripherals if you’re not using a microcontroller (uC)? [JKAbrams] and [Tim Gremalm] answered that question with this printer port (LPT) adapter. They wanted an indicator light when someone in an IRC room was talking to them. By connecting a blue rotating light through a relay to the output of this fob they’ve done just that, but there’s room for much more.

The adapter uses a Darlington transistor array IC to protect the computer. A resistor between the LPT and the base pin on the chip ensures that current flow will be well within the safe levels for the computer. The Darlington transistor amplifies the output using an external power supply in order to drive heavier loads.

If you want a deeper understanding of the printer port check out this tutorial. LPT ports are becoming less common and that’s why so many projects are migrating over to USB (plus there’s no need for external power with most USB connected projects) but if you’ve got one, it’s probably not being used for anything else.