DIY programming adapters


Sjaak writes:

Today came in a new batch of PCBs from, of which one is a new revision of the BlackMagicProbe. This revision is almost the same except it has a polyfuse in its powersupply to the target, a dedicated voltage regulator instead of P-FET, its programming header on the 90 degree on the side and a jumper for entering DFU mode. All this goodness is contained in less 5×2 cm PCB space, so quite a bit of PCB estate is left for other purposes and I used panelizing in EAGLE to try another brainfart of mine.
In most DIY projects where pogo pins are used people solder them directly to a wire or pad on a PCB. Despite it looks like it is the way to go, it isn’t. Pogo pins tend to wear out relative quickly as they are only rated for a couple of hundred ‘compressions’, also solder can sip into the pin and ruin its spring.

More details at

from Dangerous Prototypes

#FreePCB via Twitter to 2 random RTs


Every Tuesday we give away two coupons for the free PCB drawer via Twitter. This post was announced on Twitter, and in 24 hours we’ll send coupon codes to two random retweeters. Don’t forget there’s free PCBs three times a every week:

  • Hate Twitter and Facebook? Free PCB Sunday is the classic PCB giveaway. Catch it every Sunday, right here on the blog
  • Tweet-a-PCB Tuesday. Follow us and get boards in 144 characters or less
  • Facebook PCB Friday. Free PCBs will be your friend for the weekend

Some stuff:

  • Yes, we’ll mail it anywhere in the world!
  • Check out how we mail PCBs worldwide video.
  • We’ll contact you via Twitter with a coupon code for the PCB drawer.
  • Limit one PCB per address per month please.
  • Like everything else on this site, PCBs are offered without warranty.

We try to stagger free PCB posts so every time zone has a chance to participate, but the best way to see it first is to subscribe to the RSS feed, follow us on Twitter, or like us on Facebook.

from Dangerous Prototypes

Practical RF filter design

Craig writes, “RF filter design is a piece of cake these days thanks to computer design and simulation tools. But actually realizing the simulated filter response in the real world can be a completely different matter! This video provides an introduction to practical RF filter design by building, testing, and tweaking a 137MHz bandpass filter suitable for NOAA APT satellite reception.”

More info at Analog Zoo homepage.

from Dangerous Prototypes

Inside the vintage 74181 ALU chip: how it works and why it’s so strange


Ken Shirriff writes:

The 74181 ALU (arithmetic/logic unit) chip powered many of the minicomputers of the 1970s: it provided fast 4-bit arithmetic and logic functions, and could be combined to handle larger words, making it a key part of many CPUs. But if you look at the chip more closely, there are a few mysteries. It implements addition, subtraction, and the Boolean functions you’d expect, but why does it provide several bizarre functions such as “A plus (A and not B)”? And if you look at the circuit diagram (below), why does it look like a random pile of gates rather than being built from standard full adder circuits. In this article, I explain that the 74181’s set of functions isn’t arbitrary but has a logical explanation. And I show how the 74181 implements carry lookahead for high speed, resulting in its complex gate structure.

More details at Ken Shirriff’s blog.

from Dangerous Prototypes

Free PCB Sunday: Pick your PCB


We go through a lot of prototype PCBs, and end up with lots of extras that we’ll never use. Every Sunday we give away a few PCBs from one of our past or future projects, or a related prototype. Our PCBs are made through Seeed Studio’s Fusion board service. This week two random commenters will get a coupon code for the free PCB drawer tomorrow morning. Pick your own PCB. You get unlimited free PCBs now – finish one and we’ll send you another! Don’t forget there’s free PCBs three times every week:

Some stuff:

  • Yes, we’ll mail it anywhere in the world!
  • Be sure to use a real e-mail in the address field so we can contact you with the coupon.
  • Limit one PCB per address per month please.
  • Like everything else on this site, PCBs are offered without warranty.
  • PCBs are scrap and have no value, due to limited supply it is not possible to replace a board lost in the post

Be the first to comment, subscribe to the RSS feed.

from Dangerous Prototypes

App note: Fast Rail-to-Rail operational amplifiers ease design constraints in low voltage high speed systems


Migration to lower rail voltages considerations on operational amplifier designs an Application note from Analog Devices. Link here (PDF)

Movement towards lower power supply voltages is driven by the demand that systems consume less and less power coupled with the desire to reduce the number of power supply voltages in the system. Lowering power supply voltages and reducing the number of supplies has obvious advantages. One such advantage is to lower system power consumption. This has the additional benefit of saving space. Lowering overall power consumption has a residual benefit in that there may no longer be a need for cooling fans in the system.

However, as the traditional system power supply voltages of ±15 V and ±12 V give way to lower bipolar supplies of ±5 V and single supplies of +5 V and +3.3 V, it is necessary for circuit designers to understand that designing in this new environment is not simply a matter of finding components that are specified to operate at lower voltages. Not all design principles used in the past can be directly translated to a lower voltage environment.

Reducing the power supply voltage to a typical op amp has a number of effects. Obviously, the signal swings both at the input and output are reduced. The required headroom between signal and rail (typically 1 V to 2 V in conventional amplifiers), which is of lesser importance with power supplies of ±15 V, now drastically reduces the usable signal range. While this reduction does not normally increase noise levels in the system, signal-to noise ratios will be degraded. Because the designer can no longer use techniques such as increasing power supply voltages and signal swings in order to “swamp” noise levels, greater attention must be paid to noise levels in the system.

from Dangerous Prototypes

App note: Resolution enhancements of digital potentiometers with multiple devices


An old application note from Analog Devices about configuring multiple digital potentiometers to improve resolution, accuracy and programming complexity might add-up to the mix though. Link here (PDF)

Digital potentiometers usually come with standard resistance values of 10k, 100k, and 1MW at a given number of adjustable steps. If an application requires a resistance range that falls between these values, users will most likely apply a part with a resistance larger than needed scarifying resolution. Fortunately, users can parallel, stack, or cascade multiple digital potentiometers to optimize the resolution for a given application. In this article, we will share some of the ideas that may solve the challenge.

from Dangerous Prototypes

USB Infrared Toy free PCB build


Ben Kazemi built a free USB IR Toy PCB. With the USB IR Toy you can use a remote control with your computer, view infrared signals on a logic analyzer, capture and replay remote control buttons.

If you build a free PCB we’ll send you another one! Blog about it, post a picture on Flicker, whatever – we’ll send you a coupon code for the free PCB drawer.

Get your own handy Bus Pirate for $30, including world-wide shipping. Also available from our friendly distributors.

from Dangerous Prototypes

5V Regulator Cap for 9V battery


David Cook built a 5V regulator to sit atop a 9V battery:

For quick portable projects and temporary hacks, it is often faster to reuse a simple 5V regulator circuit than to integrate a power supply into the device design. My toolbox has an LED tester and magnifier light, so why not add a convenient 5V regulator cap to the collection? There are nicer ones on the market that have surface mount components, but half the fun of an electronics hobby is creating something basic in your own style. This double-decker board with flashing LED power indicator allowed me to experiment with flush battery snaps and board interconnects.

More details at David Cook’s Robot Room project page.

from Dangerous Prototypes