Learn And Build A High Side Switch

September 16, 2015 by Bil Herd 75 Comments

As electronics engineer I have a mental collection of circuits that I’ve gathered over the years, much like a mechanic collects specialized tools as they work. All engineers do this and the tools in their tool boxes usually represent their project history and breadth.

A useful circuit to have in designer’s toolbox is the “high side switch”. Like it sounds, this is a circuit that switches the “high side” or positive voltage to a load.

We usually tend to switch things to ground as seen by outputs such as an Open Collector output, the reason being that ground usually is a known entity and is usually low impedance and is at a known voltage. But there are advantages to using a high-side switch in your circuits.

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How CMOS Works: Some Final Words About CMOS

September 2, 2015 by Bil Herd 18 Comments

Finishing up on the topic of CMOS bus logic I am going to show a couple of families with unique properties that may come in handy one day.

High Voltage Tolerant Family: AHC/AHCT

AHCT w/o high side diode — Note the missing diode to VDD

First up is a CMOS logic family AHC/AHCT that has one of the protection diodes on the input removed. This allows a 5V input voltage to be applied to a device powered by 3.3V so that I don’t have to add a gate just for the translation. Any time I can translate and do it without any additional gate delays I am a happy engineer.

Of course the example above works in a single direction and bidirectional does start to get more complicated. Using a bidirectional buffer such as a 74AHCT245 will work for TTL translation when going from 3.3V back to 5V providing there is a direction control signal present.

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Core Memory For The Hard Core

August 31, 2015 by Elliot Williams 58 Comments

[Brek] needed to store 64 bits of data from his GPS to serve as a last-known-position function. This memory must be non-volatile, sticking around when the GPS and power are off. Solutions like using a backup battery or employing a $0.25 EEPROM chip were obviously too pedestrian. [Brek] wanted to store his 64 bits in style and that means hand-wired core memory.

OK, we’re pretty sure that the solution came first, and then [Brek] found a fitting problem that could be solved, but you gotta give him props for a project well executed and well documented.

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Driving A 7 Segment LED Display From An FT232

August 29, 2015 by Richard Baguley 9 Comments

Sometimes, a good hack is about using less rather than more. That’s the case with this neat tutorial from [Rahul.S] on driving a 7-segment LED display with an FT232. By using this cheap USB to serial controller, [Rahul.S] was able to drive the display directly without using a microcontroller, which keeps the component cost down.

He’s bit banging an octal buffer connected to the display. You may be surprised to find that the FT232 chips do have enough outputs to make this work. Rather than send serial data number to the display and have a controller convert this into a set of signals that make the number, this conversion is done by the PC, which then sends a signal that directly illuminates the appropriate parts of the LED. By using all of the available output lines of the FT232 (including ones like the RTS/CTS line that are usually used for signalling), [Rahul.S] was able to drive all seven of the elements and the decimal point.

Of course, cynics may argue that it would be simpler to use a cheap serial LCD display. That is true, but there is always something to be said for knowing how to do something yourself rather than letting others do it for you… Continue reading “Driving A 7 Segment LED Display From An FT232” →

Spectrum Painting On 2.4 GHz

August 22, 2015 by Elliot Williams 15 Comments

Give a software-defined radio (SDR) platform to a few thousand geeks, and it’s pretty predictable what will happen: hackers gotta hack. We’re only surprised that it’s happening so soon. Spectrum Painter is one of the first cool hacks to come out of the rad1o badge given out at the CCCamp 2015. It makes it dead-simple to send images in Hellschreiber mode on a few different SDR hardware platforms.

What we especially like about the project is its simplicity. Don’t get us wrong, we’re tremendous fans of GNURadio and the GNURadio Companion software radio hacking environment. But if you just want to do something simple, like send a picture of a smiley-face, the all-capable GNURadio suite is overkill.

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Developed On Hackaday: Let’s Build An Electronic Hackaday Badge

August 17, 2015 by Anool Mahidharia 44 Comments

We’re going to build an electronic Hackaday Badge, and by “we”, I mean Hackaday community members who are passionate about the project.

I’ll be leading the charge. I had a great learning experience the last time I helped design the e-paper badge for the 2013 Open Hardware Summit, and hope to learn a lot along the way this time too. Since then, Badges have come a long way – at cons like DEFCON, LayerONE, Shmoocon, The Next Hope, Open Hardware Summit, The EMF, SAINTCON, SXSW Create, The Last Hope, TROOPERS11, ZaCon V and of course the rad1o from this year’s CCCamp. Word is that this year’s Open Hardware Summit badge is going to be pretty kickass too. So, we have some very big shoes to fill. But this doesn’t have to be about “my badge is better than yours”. And this badge isn’t meant to be specific to any single con or event. So what does the Badge do, then? “It’s a physical extension of the hackaday.io community, made specifically for hacker gatherings of all types and sizes.”

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DEF CON: HDMI CEC Fuzzing

August 9, 2015 by Brian Benchoff 10 Comments

HDMI is implemented on just about every piece of sufficiently advanced consumer electronics. You can find it in low-end cellphones, and a single board Linux computer without HDMI is considered crippled. There’s some interesting stuff lurking around in the HDMI spec, and at DEF CON, [Joshua Smith] laid the Consumer Electronics Control (CEC) part of HDMI out on the line, and exposed a few vulnerabilities in this protocol that’s in everything with an HDMI port.

CEC is designed to control multiple devices over an HDMI connection; it allows your TV to be controlled from your set top box, your DVD player from your TV, and passing text from one device to another for an On Screen Display. It’s a 1-wire bidirectional bus with 500bits/second of bandwidth. There are a few open source implementations like libCEC, Android HDMI-CEC, and even an Arduino implementation. The circuit to interface a microcontroller with the single CEC pin is very simple – just a handful of jellybean parts.

[Joshua]’s work is based off a talk by [Andy Davis] from Blackhat 2012 (PDF), but greatly expands on this work. After looking at a ton of devices, [Joshua] was able to find some very cool vulnerabilities in a specific Panasonic TV and a Samsung Blu-ray player.

A certain CEC command directed towards the Panasonic TV sent a command to upload new firmware from an SD card. This is somewhat odd, as you would think firmware would be automagically downloaded from an SD card, just like thousands of other consumer electronics devices. For the Samsung Blu-Ray player, a few memcpy() calls were found to be accessed by CEC commands, but they’re not easily exploitable yet.

As far as vulnerabilities go, [Joshua] has a few ideas. Game consoles and BluRay players are ubiquitous, and the holy grail – setting up a network connection over HDMI Ethernet Channel (HEC) – are the keys to the castle in a device no one would ever think of taking a close look at.

Future work includes a refactor of the current code, and digging into more devices. There are millions of CEC-capable devices out on the market right now, and the CEC commands themselves are not standardized. The only way for HDMI CEC to be a reliable tool is to figure out commands for these devices. It’s a lot of work, but makes for a great call to action to get more people investigating this very interesting and versatile protocol.