Implementing A CPU Using 555 Timers And Logic Synthesis

December 17, 2021 by Dave Rowntree 26 Comments

There is many a comment on these here pages along the lines of “Why did you use a microcontroller, when you could just have easily used a 555 timer!” And, yes, we sometimes agree with the sentiment, but when a chance comment seen by Hackaday.io user [Tim Böscke] suggested turning it around and building a microcontroller out of 555 timers, the gauntlet was well and truly thrown down. Now let’s be clear, this is not the first time we’ve come across this idea, there was a breadboard 555 based build ten years ago, but this is the first time we’ve seen it done by leveraging open source synthesis targeting a PCB!

The first logic element was a simple inverter, constructed by tying the TRIGger and THReShold pins together.

LTSpice model of a NAND gate implemented with 555 and diodes

From there it was a simple matter of adding a few diode-resistor networks to the input, to effect a NAND2 gate and a NOR2 gate. Development was speeded up a bit by modeling the logic circuits in LTSpice, to find the best combination of part values. From these simple elements, all further logic functions could be implemented. Next a memory element was needed. As luck would have it, the 555 has a RS flip flop as part of its circuit, fed by dual comparator inputs. All that was needed was to bias the THRS input at Vdd/2 and then feed the data in via a pass transistor, and hey presto! a serviceable, albeit slow latch.

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Using Fishing Wire To Hold In Pin Headers Is A Nifty Trick

December 16, 2021 by Lewin Day 55 Comments

Working on a breadboard, one can get used to the benefits of being able to readily plug and unplug jumper wires to reconfigure a project. One could only dream of doing so with PCBs, right? Wrong! [Stewart Russell] recently shared a tip on Twitter on how to do just that, with the help of a little fishing wire.

The wire can be neatly threaded through the board to enable quick hookups.

The trick is simple: on any old development board that uses 0.1″ pitch headers, simply weave some fishing line through the plated through-holes in the PCB. Then, regular jumper wires can be inserted just like on a breadboard. The fishing wire has just enough give to allow the jumper wires to be jammed in, holding them steady and in good contact, while still allowing them to be easily removed.

[Hackspace Magazine] has raved about the trick, noting great success using 0.38 mm fishing line. Alternative methods involve using toothpicks, though we suspect solution is likely messier and less reliable.

If you’ve got your own tricks for prototyping quickly using development and breakout boards, be sure to share them below in the comments. Alternatively, send your best stuff to us on the tipsline!

Christmas Tree PCB Just The Trick For Festive Glee

December 15, 2021 by Lewin Day 3 Comments

The festive season is often as good a reason as any to get out the tools and whip up a fun little project. [Simon] wanted a little tchotchke to give out for the holidays, so they whipped up a Christmas tree PCB that’s actually Arduino-compatible.

It’s a forward-looking project, complete with USB-C connector, future-proofing it for some time until yet another connector standard comes along. When plugged in, like many similar projects, it blinks some APA102 LEDs in a festive way. The PCB joins in on the fun, with white silkscreen baubles augmented by golden ones created by gaps in the soldermask.

An ATTiny167 is the brains of the operation, using the Micronucleus bootloader in a similar configuration to the DigiSpark Pro development board. It relies on a bit-banged low-speed USB interface for programming, but the functionality is largely transparent to the end user. It can readily be programmed from within the Arduino IDE.

It’s not an advanced project by any means, but is a cute giveaway piece which can make a good impression in much the same way as a fancy PCB business card. It could also serve as an easy tool for introducing new makers to working with addressable LEDs. Meanwhile, if you’ve been cooking up your own holiday projects in the lab, don’t hesitate to drop us a line!

PCB Microsurgery Puts The Bodges Inside The Board

December 14, 2021 by Dan Maloney 23 Comments

We all make mistakes, and there’s no shame in having to bodge a printed circuit board to fix a mistake. Most of us are content with cutting a trace or two with an Xacto or adding a bit of jumper wire to make the circuit work. Very few of us, however, will decide to literally do our bodges inside the PCB itself.

The story is that [Andrew Zonenberg] was asked to pitch in debugging some incredibly small PCBs for a prototype dev board that plugs directly into a USB jack. The six-layer boards are very dense, with a forest of blind vias. The Twitter thread details the debugging process, which ended up finding a blind via on layer two shorted to a power rail, and another via shorted to ground. It also has some beautiful shots of [Andrew]’s “mechanical tomography” method of visualizing layers by slowly grinding down the surface of the board.

[Andrew] has only tackled one of the bodges at the time of writing, but it has to be seen to be believed. It started with milling away the PCB to get access to the blind via using a ridiculously small end mill. The cavity [Andrew] milled ended up being only about 480 μm by 600 μm and only went partially through a 0.8-mm thick board, but it was enough to resolve the internal short and add an internal bodge to fix a trace that was damaged during milling. The cavity was then filled up with epoxy resin to stabilize the repair.

This kind of debugging and repair skill just boggles the mind. It reminds us a bit of these internal chip-soldering repairs, but taken to another level entirely. We can’t wait to see what the second repair looks like, and whether the prototype for this dev board can be salvaged.

Thanks to [esclear] for the heads up on this one.

USB LED Christmas Tree Is Making Spirits Bright

December 13, 2021 by Kristina Panos 9 Comments

[Piotr SB] knows there is no way out of the holidays; the only path is through. You’ve got to find cheer wherever and however you can, so why not cater to your own interests and build the cutest little LED Christmas tree you ever did see? And did we mention it’s USB and absolutely free (as in carols, not eggnog)?

This O-Christmas tree is made up of concentric rings that are built into a tier as you solder the LEDs. And of course you’re supposed use the LED legs as supports! One leg from each LED — 18 green and a red one for the top. Because the PCB is not quite thick enough, you’ll need to add a plastic spacer to get it to stay in the USB port. Not only is this a nice design, the snowflakes and snowman on the silkscreen totally seal the cuteness deal.

Ever get so frustrated with your Christmas tree that you want to just empty a few rounds into the thing? No? Well, you’d have a good reason to if you built this Duck Hunt ornament.

Snip Your Way To DIY PCB Castellations

December 11, 2021 by Dan Maloney 22 Comments

Castellated PCB edges are kind of magical. The plated semicircular features are a way to make a solid, low-profile connection from one board to another, and the way solder flows into them is deeply satisfying. But adding them to a PCB design isn’t always cheap. No worries there — you can make your own castellations with this quick and easy hack.

[@CoilProtogen] doesn’t include much information in the Twitter thread about design details, but the pictures make it clear what the idea is here. OEM castellations are really just plated areas at the edge of a board that can be used to tack the board down to another one without any added hardware. The hack here is realizing that lining up a bunch of large-diameter vias and cleaving them in half with a sharp pair of scissors will result in the same profile without the added cost. The comments on the thread range from extolling the brilliance of this idea to cringing over the potential damage to the board, but [@CoilProtogen] insists that the 0.6-mm substrate cuts like butter. We’d worry that the plating on the vias would perhaps tear, but that seems not to be the case here.

The benefits of a zero-profile connection are pretty clear in this case, where castellated PCBs were used to replace bulky header-pin connectors on a larger PCB. We can see this technique being generally useful; we’ve seen them used to good effect before, and this is a technique we’ll keep in mind for later.

Lasers Make PCBs The Old Fashioned Way

December 10, 2021 by Al Williams 46 Comments

There are many ways to create printed circuit boards, but one of the more traditional ways involves using boards coated with photoresist and exposing the desired artwork on the board, usually with UV light. Then you develop the board like a photograph and etch it in acid. Where the photoresist stays, you’ll wind up with copper traces. Hackers have used lots of methods to get that artwork ranging from pen plotters to laser printers, but commercially a machine called a photoplotter created the artwork using a light and a piece of film. [JGJMatt] sort of rediscovered this idea by realizing that a cheap laser engraver could directly draw on the photoresist.

The laser dot is about 0.2 mm in diameter, so fine resolution boards are possible. If you have a laser cutter or engraver already, you have just about everything you need. If not, the lower-power laser modules are very affordable and you can mount one on a 3D printer. Most people are interested in using these to cut where higher power is a must, but for exposing photosensitive film, you don’t need much power. The 500 mW module used in the project costs about fifty bucks.

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