EMI shielding

Close GSM antenna proximity to bare PCB was troublesome latching microSD. Using most resilient flash cards nearly solved the problem. Extra shielding would help to prepare for worst field conditions like area of weakest GSM signal leading to highest emission and EMI. I took long and tough lesson to get shielding done right. Continue reading

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OSX mishandles SSID with @ sign

Lately at the airport so-called user-friendly Apple operating system  was stubbornly failing to log into WiFi without giving me any clues. Meanwhile Android phone was happily sucking data from the same hotspot. It turned to be an OSX (Yosemite 10.10.4) bug when hotspot uses valid for SSID “at” (@) sign. Intuintion of engineer let me quickly overrun this issue. But hey Apple, what about average Joe OSX is designed for? Continue reading

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GSM antenna freezes microSD

Dealing with RF is tricky part of electronic design, even though I never had significant issues with GSM in my prototypes. Advancing in WLS project however I discovered a nasty issue with micro SD prone to lock up on interference from GSM built-in antenna, even located in significant distance. To my surprise half of different tested brands suffered from it. Thru extra tests, selection and SD replacement action I was able to greatly improve stability of long-running system.
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External RAM and lost MCUCSR

Atmega’s MCUCSR status register gives info about restart reason like regular reset-pin shorted, watchdog initiated reset, or brown-out on low voltage from power supply. Pieces of valuable information for device defect tracking. Reading MCUCSR early in test program was fine, while in real system with bootloader and external RAM memory I always got incorrect value. It took me couple hours to pin down the problem of single incorrect byte of information. Continue reading

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100 articles

Shortest post ever: 100 articles published right after 4th blog anniversary, 4 most popular articles were viewed 100k times altogether, all articles 400k times (entry page does not count) and I still have no idea why I am doing this as total blog revenue is $0 😉

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Pimp my bus: from 8-bit AVR to 32-bit ARM

Going to newer architecture is unevitable evolution. ARM series is particularly good choice as knowledge of its core functionality is to large extent portable across manufacturers. While ARM Cortex-M chips are close to 8-bit AVRs in footprint size and price tag, they give more processing power and peripherals. More complex architecture and ultra-small packaging is often counter-argument on hobbyists forums. Does it really matter? Here is my subjective comparison of these vast families. Continue reading

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Unf*cking my mac

Beer flushed thru air vents into Macbook mainboard killed it instantly. F-words came even faster as it was done by someone sitting next to me on the airplane from Germany to USA, a guy who called it an accident, not a fault. I was not surprised that later he did not respond to my contact attempts even though we exchanged business contacts for that purpose. What surprised me was his civil cowardice, especially contrasting to his higher rank US Army officer profile. Thuck you very much Marcus! Continue reading

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Water Level Logger – Firmware over-the-air

fotaOver time firmware stabilizes but rework never entirely completes, either due to inevitable bugs or further enhancements. Manual firmware update applied to couple stations in the field has relatively low effort and is just dauting task. While number of stations grows, sparse distribution or distant locations starts to occur all that becomes significant task. Planning ahead I decided to equip the system with secure FOTA (firmware over-the-air) feature. Continue reading

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GSM workshop

Warmed up with HTC smartphone fix among other micro repairs I decided to give a chance and fix two other phones with accidently damaged displays. Both Sony Xperia Z2 and BlackBerry Z10 were given ridiculous cost estimates by authorised service and I was given green light to mess up with both unused phones. Continue reading

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Water Level Station – field tests

Solar panel, probe and main unit is part of my balcony landscape for over a year now. This setup is running from many weeks to several months uninterruptedly depending purely on firmware upgrades. Field tests being final proof are needed though mainly to simulate shallow running water in freezing weather conditions. This is why two stations were deployed before this winter. Continue reading

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