Free PCB Sunday: Pick your PCB

via Dangerous Prototypes

BP-600x373

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

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App note: Testing inductors at application frequencies

via Dangerous Prototypes

an_coilcraft_doc119

An app note from Coilcraft on inductance and Q parameters which are the important factors of an inductor and how these values are found. Link here (PDF)

The accurate measurement of an inductor has always been more difficult than the measurement of other passive components. The primary difficulty with coil measurements lies in the fact that coil inductance and its efficiency are quite frequency dependent; similarly, coil parasitics (distributed capacitance and core/copper resistive losses) vary dramatically with frequency. The measurement of a coil at the application frequency, so-called “use frequency testing,” is more representative of the basic value of the component in circuit than testing at traditional standard frequencies.

Often, the value of a measurement frequency is specified for measurement convenience alone. If the measurement frequency is not the circuit (or “use”) frequency, the result of testing generally will not yield the same inductance value or display the same efficiency as seen by the intended circuit. Given that recent developments of equipment and methods now allow more flexibility in test frequency selection, inductors should be tested at the actual frequency of use, particularly if tight tolerances are required.

App note: Working voltage ratings applied to inductors

via Dangerous Prototypes

Coilcraft’s application note about why there are no voltage ratings specified on inductors. Link here (PDF)

Voltage ratings are often specified for many electronic components, including capacitors, resistors and integrated circuits, but rarely for inductors. This article addresses the reasons why working voltage ratings are not typically published for inductors.

There are challenges to determine voltage ratings for inductors, either by testing or calculation. Inductors do not support dc or low frequency working voltages unless the inductance is high (typically >1 mH). Testing to verify working voltage can be difficult and should be application dependent. The various ways inductors are made, and the stresses of processes like wire bending, make calculating a theoretical voltage rating infeasible.

This article presents these issues to make it easier to choose an inductor most appropriate for the specific application.

AT to XT Keyboard Adapter

via hardware – Hackaday

If you got an old PC/XT stored somewhere in basement and want to use a newer keyboard, here’s a little project you might like. [Matt] built an AT2XT keyboard adapter on a prototype board using an AT to PS/2 keyboard cable. An AT2XT keyboard adapter basically allows users to attach AT keyboards to XT class computers, since the XT port is electronically incompatible with PC/AT keyboard types. For those retro computing fans with a lot of old PCs, this trick will be great to connect the XT machines to a KVM (keyboard/Video/Mouse) switch.

[Matt] found schematics for the project on the Vintage Computer Federation Forum, but used a PIC12F675 instead of the specified PIC12F629. He does provide the .hex file for his version but unfortunately no code. You could just burn the .hex file or head up to the original forum and grab all files to make your own version. The forum has the schematics, bill of materials, PCB board layout and firmware (source code and .hex), so you just need to shop/scavenge for parts and get busy.

And if you are felling really 31337, you can make a PS/2 version of the binary keyboard to justify the use of your new adapter.

[via DangerousPrototypes]


Filed under: computer hacks, hardware

Free PCB coupon via Facebook to 2 random commenters

via Dangerous Prototypes

BP

Every Friday we give away some extra PCBs via Facebook. This post was announced on Facebook, and on Monday we’ll send coupon codes to two random commenters. The coupon code usually go to Facebook ‘Other’ Messages Folder . More PCBs via Twitter on Tuesday and the blog every Sunday. Don’t forget there’s free PCBs three times every week:

Some stuff:

  • Yes, we’ll mail it anywhere in the world!
  • We’ll contact you via Facebook 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.

Single tube Lethal Nixie clock

via Dangerous Prototypes

singletubenix1-600

Andrew Moser made a lethal nixie tube clock:

Clock 1: Single tube Lethal Nixie clock — you know having all the high voltage lines exposed and un-insulated. Inspiration for this design was from this clock. Unfortunately I built mine right after having surgery. I think the painkillers had something to do with the aesthetics… Anyhow I wasn’t electrocuted while building it under the meds…That’s always a plus!
ATMEGA 328 arduino with a DS1307 RTC for timekeeping. Basically the arduino pulls time from the RTC then updates IO. During this it’s got a time based ISR that: interrupts the code, measures the high voltage, then makes necessary tweaks to the boost converter duty cycle via a proportional controller.

Project info at ReiBot.org.

Check out the video after the break.