Design Analysis of a Petzl ACTIK CORE Headlamp

Hi! It’s been a while. :-)

Since my last post here five years ago I’ve been around a fair amount, played with new toys, built few things. One thing that recently impressed me though is this little mid range Petzl headlamp.

I’ve been using it for trail running in the night for the past two years, including some fairly long adventures. As an embedded enthusiast I got more interested in the design of the little thing, so I took it apart to study it, and found many non obvious things. Let’s try to highlight some of them here!

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LNA for RTL Based SDR Receivers

SDR is one of the trendy technologies of the moment, and I couldn’t resist the temptation to buy one of those cheap RTL2832U based DTV receivers, usable out-of the box as a SDR.

The device comes with a fronted (R820T) with a built-in LNA, which is normally powerful enough to fed the receiver when using a short cable, but since I wanted to experiment with an antenna mounted on a relatively long and thin cable, I built a small LNA to be mounted at the far end, near the antenna.


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The LNA is based on the Mini Circuits PSA4-5043+, and the board is designed to be as small as possible to fit in line with the antenna and cable, and to be powered by the receiver itself.

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Breakout Board for Wireless Devices Using the Nordic nRF24L01+

Recently I’ve been playing a lot with sensors around the house and I’ve decided to make myself a breakout board with all of the common parts the sensor board, including the power supply, microcontroller, wireless interface and
battery charger.


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This board can be used to quickly deploy some sensors or actuators, and can be configured to work from battery (for low power applications) or from an USB port (to be used with phone charger). The PCB fits into an Hammond 1551R box.

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Power over Ethernet Flashlight

Sometimes you learn about an interesting IC and you build an entire circuit around it for no other good reason… This project is one of those!

The TPS2378 is an IEEE802.3at (Power over Ethernet) Powered Device controller, featuring internal pass MOSFET for loads up to 25.5W, Type 1 (a.k.a. 802.3af) compatibility and auxiliary power source support.

The IC is normally used together with a DC-DC step down regulator to power a network device (the PD) from a PoE compliant switch or injector (the PSE). A proper 802.3at device requires an isolated power supply with some safety characteristics that makes it not trivial to implement, and there are many DC-DC ICs with integrated PoE controller to make it easier, but as I wasn’t really interested in that part I just went for an easier project with just the PoE controller and some ballast… And what better ballast than some high power white LEDs!

This project is a small PoE flashlight, that can be powered by any 802.3af or 802.3at compliant injector or switch. It can be used as a PoE tester, or if you get trapped in a dark datacenter at night!


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LED Light Replacement for AC Halogen Lamps

LED based home lights are becoming more and more common each day due to their higher efficiency, and their price is starting to fall to an affordable level. Most commercial AC LED lights on the market are meant to replace 230V E27 lamps, as that socket is big enough to fit an AC/DC converter inside.

I have recently found myself with some floor and roof halogen lamps that I wanted to convert to LED, but I wasn’t able to find a commercial replacement for the 12V AC powered G4 lamps and I did not want to replace the power supply, so I decided to run my own design!


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This project is a small LED based lamp designed to replace AC halogen bulbs, and to fit in a small 3cm diameter PCB.

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Hacking into a Vehicle CAN bus (Toyothack and SocketCAN)

CAN bus is an automation fieldbus commonly used in the automotive industry as the main network bus to allow communications between the many on-board ECUs on modern vehicles.

The Linux kernel has native CAN bus support at network layer since some years, with a lot of drivers for both embedded and USB CAN bus controllers, so it’s now fairly easy to add a CAN bus interface to any Linux laptop and have a playaround with it.

In this post I’ll show how to tap into a modern car local bus, dump a bunch of data and analyze the trace offline to write a decoder from scratch using the SocketCAN APIs and utilities.

This is based on my experiences hacking into my Toyota… Toyothack!


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Inside a Hantek DSO-2090 USB Oscilloscope

As part of my electronics test gears, I’ve recently got myself a cheap USB oscilloscope: a Hantek DSO-2090.

The DSO-2090 is marketed as an 100 MSPS with 60 MHz analog bandwidth, though the full sample rate is available only when using a single channel. As Hantek also sells similar models with higher performances, I immediately took the device apart to better understand how it works and to see if it can be pushed a bit more, especially regarding the realtime sample rate.


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This post is a basic analysis of how this oscilloscope works with some consideration of its limits, and it may be interesting to better understand how a basic DSO works.

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USB to 100BASE-FX Optical Fiber Network Card

Optical fiber is an intriguing technology, deployed all over the world connecting computer networks with the speed of light (well… almost).

Unfortunately, due to the inherent complexity of fiber network installation and management, optical fiber devices have never found their way in the hands of the user, and are usually deployed only by professionals for things such as backbones, long hauls or really fast interconnections.

Luckily enough, older optical fiber Ethernet components, especially 100MBit ones, are now available as a reasonably low price, so I decided to design a couple of USB to 100BASE-FX network cards just for fun and to learn more about working with optical fibers.

This project contains two complete hardware designs for USB to 100BASE-FX network cards, one with a 1×9 transceiver and one with an SFP slot. Both designs are based on the ASIX AX88772B chip, and fit in a compact Hammond 1551 series box.


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Also, there are some useful links and information about designing with OF transceivers and SFP modules.

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Power Manager: Soft Power Control of USB and Low Voltage Devices

One frustrating aspect of firmware or kernel development on commodity hardware, such as cheap evaluation board or production devices, is the necessity of power-cycling the target device to reboot it every time the developer needs to load and run a new software build.

It sometimes happens that a development board is designed with proper management electronics to ease software development or automated testing, but in most cases the developer has reset the board manually, and sadly quite often reset buttons are unaccessible or just non-existent, requiring the developer to unplug and replug the power cable. If this ends up in your workflow and at the end of the day your fingers hurt, something is wrong.

This project is a small AVR/V-USB based board to control the power supply of development boards and other low voltage and USB powered devices. It allows to program a sequence of events for the output ports, has LED indicators for port status, and additionally provides power measurement on both USB and main power channels, and uses a bootloader for easy firmware upgrade… All in a solid and funny looking Hammond blue box!


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HP Wi-Fi Direct Mouse on Linux

In my last post I took apart an HP Wi-Fi Direct mouse based on the OZMO2000 controller from Ozmo Devices.

OZMO based devices are officially supported on Windows 7 platform only, rendering them completely useless as nobody uses Windows anymore… right? Well, it turns out most of the code to use them in Linux is already in place, just waiting to be enabled!


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Wi-Fi direct support in Linux is quite young and still considered as experimental, so read on if you dare to try!

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HP Wi-Fi Direct Mouse Teardown

Wi-Fi Direct (also known as Wi-Fi P2P) is an extension of the 802.11 stack, allowing compliant devices to communicate directly, without requiring their disconnection from the main access point. The technology re-uses many existing standards and can be seen as the capability of a wireless device to have multiple logical interfaces in different modes, including some in master/softAP mode with WPS.

Wi-Fi Direct attracted the interest of gadget device makers, as it allows to re-use existing network cards to connect external devices wirelessly and without the need for an additional dongle.

One of the first device to appear on the market is the HP Wi-Fi Direct Mouse… Want to see what makes it tick? Keep reading!


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Eagle Library for Hammond 1551 Boxes

Hammond Mfg is an American company who makes many different product boxes, mostly famous for their aluminum “Stomp Box” series, widely used for both DIY and commercial guitar effects units.

Browsing through the company’s products, you can find a whole range of small translucent plastic boxes that are really well suited for small electronic PCBs, and can give a good product-ish look to any hobby project.

In this post you’ll find some hints for designing PCBs for Hammond boxes, and an Eagle library with PCB outlines for some of them.

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USB Current Meter

…or USB power meter?
…or USB KEY AVR Tiny split core interface?

Call it however you want, this project is a small USB key sized circuit to interface an USB system with a single split core current sensor using an ATtiny85.

These non-invasive sensors are widely available on eBay and similar for a reasonable price (around USD$ 30 for the one I used) and let you measure the current flowing through an alternate voltage line, like house mains. This can be used to get a gross measure of instantaneous power consumption, allowing you to make a graph out of it and plot your power usage profile, or just to check how much power a device is using.

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A friend of mine is using this one side-by-side with its photovoltaic inverter to upload his data on pvoutput.org, a nice website for photovoltaic plant monitoring.

This also shows a rectifier circuit to acquire data from an alternate voltage source without dual power rails.

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Making Time Lapse Video with IP Cameras

What happens when you find yourself with two IP cameras which you don’t really use? You just make some funny stuff with them!

This post shows how to use an Axis IP camera and a netbook to record a timelapse video of a car travel… including a 15 minute timelapse of car trip from Italy to Germany!

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DIY Cheap Internal WiFi Antenna

Some time ago I put my hand on a couple of broken Axis network cameras which were about to be trashed. These cute small devices have an image sensor with a plastic lens, a wired and a WiFi interface to connect to an external network, and many other nasty features.

The cameras had a busted Marvell power supply, which probably broke ahead of time because of the high working temperature, and once replaced with an LD1117 (I know, not the best of choices…) they were as good as new.

The one thing I did not like about these cameras was the cheap WiFi antenna, which is mounted far away from the casing and gives an old bulky feeling to the device.

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This post is a tutorial on how to build an internal WiFi antenna to modify this kind of devices!

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