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Sylvain Leroux
Lives in Lorient, France
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Sylvain Leroux

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Un incroyable potentiel pour une taille rikiki. Qui aurait pu imaginer il y quelques années seulement un système embarqué basé sur un processeur de classe Pentium guère plus gros qu'un timbre poste...
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Sylvain Leroux

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Got many many difficulties interfacing a Raspberry Pi to a 3.3V serial device through FTDI-based USB<->serial adapter! I'm now giving a try to direct access to the board serial port.

http://jeelabs.org/2012/09/20/serial-hookup-jeenode-to-raspberry-pi/
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Sylvain Leroux

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I bought a bunch of these IDC connectors for 28 AWG ribbon cable, missing the fact than a special tool is required to mount the cable on the connector.

http://www.digikey.com/product-detail/en/06ZR-8M-P/455-2293-ND/1678837

The dedicated crimping tool is far beyond my budget. And the "brute force" approach using multigrip pliers wasn't very convincing either... 

Do you know any low cost/hackish way to crimp the cable in this kind of connector?
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Bill Sidhipong's profile photoRick Fluck's profile photoReinoud de Lange's profile photoThom Thomas's profile photo
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Look into punchdown tool with changeable tip. That, or small flat screwdriver.
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Sylvain Leroux

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Electrical engineering trivia quiz #4

OK, you're good! So this one is little bit trickier -- or, to be more precise, it will require creative solution(s).

I2C is a popular communication protocol in embedded systems. Being synchronous, the I2C protocol require two communication lines: SCL (the clock) and SDA (for data). On your I2C bus you usually have one MCU acting as a master, and one or many slave devices (sensors, EEPROM, ...).

Electrically speaking, (i.e.: at physical layer) I2C is an open-collector protocol: each chip (incl. the MCU) is able to drive the line low, but is unable to drive it high - and so require pull-up resistors on the bus line.  The reason is to allow a wired AND on the bus line which is required for proper operations of the I2C protocol. Even without dedicated I2C port, it is easy to emulate I2C protocol on many (if not all) MCU by using a pair of three-state output pins 

All of this is the classical description of I2C as you might find it by googling a little. But I don't like pull-up resistors. I have always the feeling those are "little vampire" -- in this particular case, eating as much as 1.4mA when both SCL and SDA are driven low by a chip on the bus (considering Vcc = 3.3V and R = 4.7kOhm). This is not much, but it could exceed by 4x or 5x the power consumption of the useful devices on the bus...

So, for the sake of my mind, could you find a more power-efficient design in order to communicate with I2C devices ... or do I have to live with those pesky watt-eater lurking on my board. Brrr... 
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Tracy Hall's profile photoBill Sidhipong's profile photoSylvain Leroux's profile photoByorn Pioquinto's profile photo
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Not much participants this time -- but interesting comments as usual !

The two pull-ups in my schematic use 1.4mA at worst - and 0.7mA on the average while the bus is active. As +Patrick Ludwig  suggested this is not that much considering the bus is idle most of the time. And,  to cite +Tracy Hall, consuming "virtually no power" at rest.

Moreover, as Patrick noticed, power is not the same thing as energy. And comparing the energy wasted in I2C communication vs energy consumed by the whole system could let one think the former is negligible. Well ... with chips consuming on average 1mA or more certainly. But ... considering for example the Atmel AT24C04C I2C EEPROM. This is not a too _un_common chip having 1mA max consumption while reading (which implies I2C bus activity) -- but with standby+leakage current < 20 µA (I2C bus idle at the same time). Maybe I made a wrong assumption here, but it seems to me that my two pull-ups will count for 30-40% of the whole power consumption.

In order to reduce the overall consumption of the I2C devices, +Bill Sidhipong came with the interesting idea  of using a spare MCU pin as voltage reference for the pull-ups. This won't help much for the reasons explained by Tracy. But ... it could reduce the whole system consumption if that voltage reference serves as well as power pin for the slave devices. Allowing to shutoff the slave devices while unused. As a matter of fact, I tried this in my latest design --  I will make some measure as soon as the PCB will arrive -- that is after the Chinese new year :D

Anyway, for the sake of this quiz, I don't like pull-ups. So I searched through the internet a way to replace those used on an I2C bus. And I came to a creative ... well, hacky or tricky solution (where's the limit? ;) . Tracy wasn't far away while speaking of active drives. The solution I found is to replace each pull-up by two inverters [1]. Those would act as weak bus holders, keeping the bus at low or high state with a very small current (depending the chip). The main drawback however is this trick can only hold the bus at a given state, and so require active transition from low to high. Saying this more clearly, in order the produce a high level on the line, the MCU has to actively output a high state and just after, switch to high impedance. The "active output" will force the bus to high state, which is hold after that by the inverters. Of course, this is no longer genuine I2C. But in a simple configuration (one master few slaves) and with tolerant chips, this should work. 

[1] http://www-personal.umich.edu/~ppannuto/research/ipsn12-i2c-paper.pdf
[2] http://www-personal.umich.edu/~ppannuto/research/ipsn12-i2c-poster.pdf

I liked that idea, that's why I share it here. Unfortunately, I don't have very low consumption inverters at hand to try it. And I guess it will require some minor adjustments (I feel like it needs some current-limiting resistors somewhere). But it definitively worth trying. Any volunteer :D ?
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Sylvain Leroux

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Anyone ever worked with Programmable XBee PRO?
(XBP24BZ7WITB003)

- Does it communicate with XBee S2 device w/ mesh network?
- Are we tight to the Digi provided  dev kit / Windows, or is there some open source Linux compatible tools available?


http://www.digi.com/wiki/developer/index.php/Programmable_XBee_-_Getting_Started
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Sylvain Leroux

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Anyone ever worked with Programmable XBee PRO?
(XBP24BZ7WITB003)

- Does it communicate with XBee S2 device w/ mesh network?
- Are we tight to the Digi provided  dev kit / Windows, or is there some open source Linux compatible tools available?


http://www.digi.com/wiki/developer/index.php/Programmable_XBee_-_Getting_Started
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Sylvain Leroux

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Got many many difficulties interfacing a Raspberry Pi to a 3.3V serial device through FTDI-based USB<->serial adapter! I'm now giving a try to direct access to the board serial port.

http://jeelabs.org/2012/09/20/serial-hookup-jeenode-to-raspberry-pi/
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... this is in fact really easy to use. Just connect RX/TX/3V3/GND a little bit of configuration et voilà!

The only drawback are, by doing so, I'm limited to only one serial device, I loose the ability to use the serial port for other purposes (logging) and, from a final user perspective, it is less appealing than just having to plug/unplug an USB cable to connect/disconnect a device.

But at last, it works! No more packet lost. No more RPi freezing under Raspbian...
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Sylvain Leroux

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J'aurais du intituler "lire écrire et décoder" un fichier binaire. Parce que c'est surtout la dernière partie qui est est la moins communément décrite dans les tutos du même style...
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Sylvain Leroux

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Et si... collision des époques où acteurs et films de légende se mélangent pour nous donner envie de traverser le mirroir!
 
Imagine famous movies, but made in another era.
These are brilliant, both artistically, & conceptually.
http://www.behance.net/gallery/Movies-From-An-Alternate-Universe/2783319
Via +Andrew Pam 
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Sylvain Leroux

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Electrical engineering trivia quiz #4

OK, you're good! So this one is little bit trickier -- or, to be more precise, it will require creative solution(s).

I2C is a popular communication protocol in embedded systems. Being synchronous, the I2C protocol require two communication lines: SCL (the clock) and SDA (for data). On your I2C bus you usually have one MCU acting as a master, and one or many slave devices (sensors, EEPROM, ...).

Electrically speaking, (i.e.: at physical layer) I2C is an open-collector protocol: each chip (incl. the MCU) is able to drive the line low, but is unable to drive it high - and so require pull-up resistors on the bus line.  The reason is to allow a wired AND on the bus line which is required for proper operations of the I2C protocol. Even without dedicated I2C port, it is easy to emulate I2C protocol on many (if not all) MCU by using a pair of three-state output pins 

All of this is the classical description of I2C as you might find it by googling a little. But I don't like pull-up resistors. I have always the feeling those are "little vampire" -- in this particular case, eating as much as 1.4mA when both SCL and SDA are driven low by a chip on the bus (considering Vcc = 3.3V and R = 4.7kOhm). This is not much, but it could exceed by 4x or 5x the power consumption of the useful devices on the bus...

So, for the sake of my mind, could you find a more power-efficient design in order to communicate with I2C devices ... or do I have to live with those pesky watt-eater lurking on my board. Brrr... 
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Have him in circles
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Très bon photographe capable de dépoussiérer même un sujet aussi éculé que les photographie de mariage! Professionnel et sympathique, Hervé Cohonner sait diriger même les sujets les plus timides pour obtenir un résultat qui sort des sentiers battus. Je recommande chaudement.
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