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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!


https://fabiobaltieri.files.wordpress.com/2013/03/pm-intro1.jpg


https://fabiobaltieri.files.wordpress.com/2013/03/pm-intro2.jpg

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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.

https://fabiobaltieri.files.wordpress.com/2012/09/power-head.jpg

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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Linux Kernel Device Drivers for AVR V-USB Devices

V-USB is a really convenient library to implement USB communication between an AVR microcontroller and any USB host enabled system.

The host side software for a V-USB device is usually handled either from a class driver, such as for HID-compliant devices, or from an userspace libusb-based application.

This post shows how to implement a Linux kernel device driver for a simple ep0-based V-USB device.

https://fabiobaltieri.files.wordpress.com/2012/05/vusb-kernel-intro.jpg
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AVR Watch

Following the trend of doing things just-for-fun, this is a wrist watch using an AVR microcontroller and 7-segment display!

Features:

  • Open firmware and hardware design files
  • AVR and V-USB based
  • Uses SMD 7-segment display – retro look!
  • Integrated USB Maxim battery charger
  • Shows how to scan-drive 7-segment displays without external components

Drawbacks:

  • Short battery life (less than one week with a 100mAh LiPo battery)
  • Tricky to hand solder (if you don’t have an hot air station)
  • Makes people thinks you are crazy (I should put this one on “features”…)
  • Looks like a small time-bomb, I would not wear it while in an airport

https://fabiobaltieri.files.wordpress.com/2012/04/avr-watch-wrist.jpg

As most of my design, I made this one because I had some 7-segment display laying around and I wanted to build something with those (that’s also why I don’t have a project BOM). Also, I like the idea of having a DIY watch which looks like a lab power supply (it also displays battery level in Volts).

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USB Sensors with ATtiny Microcontrollers

Working with embedded electronics, you will eventually ends up with some sensor between your hands, here I’ll show how to make a graph out of it!

This project involves a light sensor, a tiny 8-pin AVR USB key with the V-USB stack, a GNU/Linux system and rrdtool.


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FTDI based USB to UART/485 Interface

If you work with embedded electronics, UART ports is something you’ll probably use every day to interface with all your SoCs and microcontrollers. As modern PCs and laptops almost always lacks legacy serial ports, you need a good USB to UART interface for all your serial needs.

USB to RS232 interfaces are easily founds online and in computer stores, but if you need RS485 and TTL UART ports you may have some problem finding the right tool.

This projects is a compact USB to TTL UART or RS485 converter, based on the popular FTDI FT232 chip. It features 3.3V TTL UART operation and an 8P8C connector (sometimes referred as RJ-45) with on board termination and bus power injection options for 485 port.

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Fun with ATtiny and V-USB

Sometime you have to do build just for the fun of it.

Recently, while I was about to order a set of PCBs from my favorite website, I told a friend about a really funny project based on the V-USB stack with ATtiny devices, and he was impressed by the size of the thing… So I decided to design my own ATtiny V-USB board!

This project is a really small USB gadget without any specific I/O, and it’s designed to fit into a USB connector with the exposed PCB as small as possible.

The original idea for this board was to use it for April-fool like jokes, but the project also uses a couple of interesting features of the V-USB stack.

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