DIY USB power bank from laptop battery


DIY USB power bank made from an old laptop battery from DoItYourselfGadgets:

A situation many can relate to: an empty smartphone battery and no outlet around! That’s exactly why I recycled an old laptop battery into an USB power bank.
This article will show you the basic powerbank circuit consisting of Lithium cell charging circuit, boost converter and toggle switch as well as my improved version with self activating boost converter and LED status indicator and homemade housing.

More details at DoItYourselfGadgets project page.

Check out the video after the break.

Breadboard line driver module


Scott from SWHarden has published a new build:

Line driver chips are one of my go-tos for quickly amplifying digital signals because they’re so fast to drop in a breadboard and they provide a strong output with very high impedance inputs and need no external components. Individual buffer of the integrated chip can be paralleled to multiply their current handling capabilities too. One of the common variants is the 74HC240.

More details at SWHarden homepage.

Outmoded Sequencer project


LuckyResistor made a miniature music machine -the outmoded sequencer project and wrote a post on his blog detailing its assembly:

I just started an interesting new project: The Outmoded Sequencer Project. It is an minimalistic music machine. You can use a 8×8 “programming” matrix to create simple melodies which are looping endlessly. This melody can be changed while the device is playing it. Here a short demonstration

My goals for the project were:

  • No microcontroller
  • Only outmoded, basic and cheap components
  • As minimalistic as possible
  • Maximize the fun with these limitations

Project info at Lucky Resistor’s blog.

Check out the video after the break.


Dekatron tubes controlled by Arduino

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Flathagen writes:

Interfacing dekatron tubes with a microcontroller is fairly easy, once you understand how the tubes work. Threeneuron’s Pile o’Poo of Obsolete Crap provides the necessary background information and schematics for making this work.
I used two russian OG-4 tubes. I prefer the orange look of the neon tubes rather than the purple look of the argon filled OG-3 tubes. The latter tubes just look to modern for my liking. On the above picture you can see how I have mounted the tubes on a rig alongside two Magic eye tubes.

More details at DIYcrap blog.

Check out the video after the break.

Light following bristle bot


Facelesstech made a light following bristle bot and wrote a post on his blog detailing its assembly:

There is one thing missing from all my projects so far…..Something that moves. Bristle bots are very similar to hex bugs but are built from toothbrush heads and pager motors. I thought the idea of bristle bots was cool but they were no brains to them until i seen this blog post where you could control one with a light. Essentially this light following bristle bot is just two bristle bots side by side so it would be steered.

More info at Facelesstech’s blog.  Project files available on github.

Check out the video after the break.

25 watt hybrid EL84 tube amp


Ray Ring from Circuit Salad has published a new build, 25 watt hybrid EL84 tube amp:

This is my new  hybrid guitar tube amp which utilizes a solid-state input stage, DSP reverb, and solid-state phase splitter. Only the push pull, class AB output stage utilizes tubes, namely two EL84’s run at 390 volts with cathode bias. The bias uses two 15 volt zeners which creates a bias current of about 26mA. This requires almost 30 volts of swing on the grids to drive the amp to saturation. This is accomplished with a little switch mode boost converter that generates 29 volts to drive the phase splitter opamps. All of the solid-state circuitry runs off the AC filament supply for the tubes. The solid state portion is basically my stomp amp design( also on this blog) minus the final power amp, which is replaced with the phase splitter.

More details at Circuit Salad’s homepage.

A low-voltage disconnect for 12 volt lead acid and lithium batteries


KA7OEI writes:

The avoidance of overcharging is usually pretty easy to avoid: Just use the appropriate charging system – but overdischarge is a bit more difficult, particularly if the battery packs in question don’t have a “protection board” with them.
Lead acid batteries (almost) never come with any sort of over-discharge protection – one must usually rely on the ability of the device being powered to turn itself off at too-low a voltage and hope that that threshold is sensible for the longevity of a 12 volt battery system.
Many larger (e.g. >10 amp-hour) lithium-iron phosphate (LiFePO4) do not routinely come with “protection” boards unless it is ordered specially: Such batteries include some of those “Lead Acid” replacements and some of the more “raw” LiFePO4 batteries available from many vendors, such as the 20 amp-hour modules made by GBS.
While it is also important to equalize LiFePO4 batteries when charging (refer to this post – Lithium Iron Phosphate (LiFePO4) batteries revisited – Equalization of cells – link) the more immediate danger in routine use is accidental over-discharge.
For lithium batteries, one may install “protection” boards that prevent accidental over-discharge and, in some cases, provide charge equalization – but such things are much rarer for lead-acid batteries, but such a circuit is quite simple and is applicable to either Lithium or Lead Acid batteries.

More details at KA7OEI blog.

DIY ECG with 1 op-amp


A DIY ECG made from single op-amp (LM741) and 5 resistors by Scott Harden:

I made surprisingly good ECG from a single op-amp and 5 resistors! An ECG (electrocardiograph, sometimes called EKG) is a graph of the electrical potential your heart produces as it beats. Seven years ago I posted DIY ECG Machine on the Cheap which showed a discernible ECG I obtained using an op-amp, two resistors, and a capacitor outputting to a PC sound card’s microphone input. It didn’t work well, but the fact that it worked at all was impressive! It has been one of the most popular posts of my website ever since, and I get 1-2 emails a month from people trying to recreate these results (some of them are during the last week of a college design course and sound pretty desperate). Sometimes people get good results with that old circuit, but more often than not the output isn’t what people expected. I decided to revisit this project (with more patience and experience under my belt) and see if I could improve it. My goal was not to create the highest quality ECG machine I could, but rather to create the simplest one I could with emphasis on predictable and reproducible results. The finished project is a blend of improved hardware and custom open-source software, and an impressively good ECG considering the circuit is so simple and runs on a breadboard! Furthermore, the schematics and custom software are all open-sourced on my github!

Project info at Scott Harden’s blog.

DIY PCB inspection microscope


Saulius made a DIY PCB inspection microscope and wrote a post on his blog detailing its assembly:

Despite how good microscope you have, stand is still very important part of final assembly. And while there are many commercial ones made of cast iron, they might cost more than a microscope head itself. I decided to make stand from wildly available material laying around – it’s MDF (Medium Density Fiberboard). Advantages – stable over time if not exposed to water, dirt cheap, easy to process.

More details at Kurokesu site.

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