GSM workshop

New life of Z10

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

IMAG0452

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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Micro-repairs

HOX unibody: back with antennas (left) and boards stack with display

Modern microelectronics assembly requires clockmaker or robotic precission; sub-millimeter discrete components or pinout of integrated-circuits is nothing unusual. Building such highly integration devices from scratch at home is a virtually impossible, sometimes though fixing them with entry-level tools is still feasible. Continue reading

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Water Level Station – rain gauge

Davis 7658M rain gauge

Measuring water level is fundamental goal of WLS experiment, hence its code-name (Water Level Station). Early summer 2014 hardware and software system had enough base services to make addition of entry-level pluviometer easy. Prior to PCB redesing for chinese factory I blueprinted and bread-boarded extra input circuitry in couple hours. Software part took me couple more days and my balcony-mounted station started measuring precipitation mid summer season. Continue reading

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Petra

petra-treasury

Visiting Jordan three years ago I was thrilled by the outstanding Dead Sea. Choosing seaside I had no time for Petra. Once I was requested to get there again I instantly knew where to go this time. Attracted by ancient city with thousands of carvings in rock with the iconic Treasure temple, place of Indiana Jones shootings, I decided to make a run through the rose red desert place. Continue reading

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Power cycling slave on I2C bus

TXS0102 voltage shifter

With the advent of 2nd revision of WLS experimental hardware I got nasty system freezes on ported firmware. As they happened always close to power cycling of probe section I suspected new ADC chip using I2C bus. Past experience with I2C drivers freezing system led to tests revealing bus corruption caused by non-deterministic behavior of slave during transient power rail states not isolated on time by the TXS0102 voltage shifter. Continue reading

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SIM900A fixed for Europe

SIM900A-closeup

So you got SIM900A, cheaper version of SIM900 with the same pinout/functions and 2-band instead of 4-band GSM radio, just to stumble on logging to network. While its great for Asian GSM infrastructure in different places in the world you will just get “PH-NET PIN” response meaning its locked for current network. I found that flashing SIM900A with firmware for SIM900 opens it up again to work exactly as SIM900, with slightly worse signal quality due to physical radio differences. Continue reading

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3D printing at home

Knot 7-1 ready

These days turning imagination into reality at home is more real than ever. RepRap movement made fused deposition modeling technology affordable. Turning a figurine or mathematical object into physical object is exciting and funny and using 3D printer to fabricate mechanical constructions or replacement parts makes it another tool on a workbench. Yet 3D printing is far away from “Ctrl+P… ready” approach. Continue reading

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PCB from Chinese factory

Small batch hotair soldered

Working prototype device made of modular PCBs let me go for the next step. Learning the process of professional PCB production in factory and making short series to scale out number of devices in the field. I had to get good grasp of CAM processing, gerber files review etc. but what bothered me more was the price. With the advent of internet services for prototyping it become easier and as always Chinese had beaten the others.
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Water Level Logger – insufficient RAM

mega128-sram

For prototype I estimated that 128kB or flash would suffice and I was right; firmware took 75kB even though fatten up by embedded strings used across the code for tracing. On the other hand 4kB RAM of Atmega128 turned to be almost insufficient: I had to tune stack sizes of tasks with ten-bytes precision. Tests were running for weaks without problem, yet extra function added in chain of calls could potentially corrupt memory. I had to make more room to avoid hard to debug problems before field deployment. Continue reading

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