Projects of Jaanus Kalde

I am using much free software and I though to recommend some better ones. Like all linux programs, they all run on Window and maybe even Mac.

• KiCad- The best free electronics CAD
  • http://www.kicadlib.org/ - Good source for libraries
  • http://kicad.rohrbacher.net/quicklib.php - online library part generator
  • http://cyclerecorder.org/footprintbuilder/ - module generator
  • http://jaanus.tech-thing.org/everything-thats-not-hardware/tech-thing-kicad-library-manager/ - library manager
• Gerbv - View you gerbers and delete unwanted parts
• gerbmerge - Merge your gerbers to one big panel
• Visolate - Gerber to milling optimized gcode "It will truly violates your eyes."
• Printrun - Controlling printer and sending gcode to it.
• Falstad circuit simulator - Simulate simple electronics with perfect components. Perfect for learning and testing simple things.
• HTerm - Terminal client. It hates processors, but the GUI is too useful to hate it.
• HeeksCAD -  The best free 3d CAD
• SMath Studio  - Free and cross platformish MathCad clone.
• Geany - Good and fast IDE for every languange.
• yEd - Best graph making program I have used. Use every time you encounter documentation.

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Cheap voltmeter in action

I bough 3$ digital DC voltmeter from ebay. I needed one for my power supply and I have became too lazy to build such things myself. It looks awesome, is not very precise. I found SMD potentiometer from the back that calibrates the voltage for about 1V, so, yea. Not precise at all. So, teardown time!

PCB of the voltmeter

PCB is reasonable quality, two sided, plate through holes. SO-16 package in the middle that does all the work, part number is sandpapered off. I searched a bit and now I know that it is not a AVR nor a PIC. Probably not ASIC either because cheap chinese things have these in die bounded to PCB, but you never know. Pin 1 is GND and pin 2 is Vcc. Power circuit has protective diode in series and then 3.0V SOT89 regulator with 10µF tantalum capacitor for power. The display is 3x 7 segment display with dots. It has 8+3 pins so everything is multiplexed, bad for me, I wanted to change the comma position.

The input goes through 330k resistor and 4.7k potentiometer, so it should affect the input by about 1.5% of the full 100V scale. There is 10k resistor and 10µF tantalum between signal and input. So, some heavy low pass filtering and about 1/34 voltage divider. The input signal goes to pin 14.

Bottom side of the voltmeter, just some tracks

I tore it apart to see if it can be easily modified to a ammeter. The cheapest ammeters cost about 3-5x more than voltmeter. To modify it to ammeter I have to modify voltage divider ten times smaller to measure shunt voltages from 0-1V. Also more of an visual thing - I have to move the dot one place left. But the placement of the dot is determined by the chip, so I can't move it. I can use it for my own purposes but I can't sell an unit with wrong comma placement, even to a friend. Damn.

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Size comparison top one was last version of Half Ohm. Bottom one is the battery of new one.

As the first version of Half Ohm milliohm meter design had some fatal design flaws, I designed a new board. The problems with the old one was that the small BR1225 battery was rated to maximum of 1mA and couldn't handle the 5mA current draw of my circuit. The second problem was that the pinout of the op-amp was wrong. For whatever reasons the pinout standards for sub 3€ op-amps and above 3€ op-amps is different.

Half Ohm board after milling.

The new schematic is basically the same, only the board got rerouted and sized up to accommodate bigger and more standard BR2032 batteries with maximum output current of 10mA. I milled the board with my 3d printer using visolate (it truly violates my eyes). The board looks weird but works very well, so I already ordered some from the factory.

When connected to the multimeter, turned on and not probing anything, the meter shows the battery voltage. When probing, then the multimeter displays mΩ in mV range. So 135mV means 135mΩ of resistance. Since the probes have considerable resistance (In my case 77mΩ) it is nice to have relative/offset/zero button on your multimeter, because then you don't have to subtract the probe resistances. I could have done it with four wire measurement, but I wanted to keep things simple. I tested my meter against commercial 4 wire meter and the result stayed in calculated 1% error. I am pleased.

Half Ohm prototype ready

A bit of technical details: The board now draws about 4.7mA so I should have about 40 hours of use. I tried to measure the 1.24V±0.5% voltage reference with my VICHY VC 97 (0.5% + 4 digits) and I got 1.247±0.006V as a result. Remeasured it with Mastech MY-64(0.5% + 1 digit) and the result was 1.241±0.004V. I tend to agree with the Mastech result a bit more, as Mastech isn't some weird ebay brand.

Half Ohm milliohm meter in action

Here are some random measurements I did in the lab.

• 77mΩ - Test probes
• 19mΩ - 18AWG Silicone cable with soldered cold connectors
• 125mΩ - Tweezers
• 5mΩ - 1cm long 2mm wide tin plated track
• 5mΩ - GND plane over 3cm of pcb
• 26mΩ - 1cm of 0.2mm trace
• 2mΩ - a 0.3mm via

As you can see it is quite useful for measuring tracks. I have already used it couple of times to find short circuit. One of my friend in lab used it to determine if his new idea of making vias is good enough. Quite awesome little tool. Next up - manufacturing units and recalculating the error with better formulas.

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tinyDino bottom view

I finally built tinyDino. I used AtMega168, so it is 100% compatible with Arduino IDE, just choose "Arduino Pro or Pro Mini (3.3V 8MHz) w/ Atmega168" as your board and it will work.

I built some and will sell them. Also, there is some more pictures:

The Smallest Arduino clone ever!

Toode on laos

Hind: 10.00€

Kogus

tinyDino top view on a 1 € cent

tinyDino with UART cables soldered

Bottom view and pad layout

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I started to build my own reprap clone about a year ago, now, finally it is almost making something useful. I used way to build that shouldn't ever be used: I took reprap Mendel design and started to make it with hand tools. Now I know that RepStraps are made for hand making and repraps are made for printing, stupid me.

My Generation 3 electronics, mounted in the bottom

I am using Generation 3 electronics, before I started, they weren't deprecated, but apparently they are now. Finally. I have much to rant about them. They use expensive and BIG connectors, like RJ45, IDC, screw terminal and what else. There is no standards in connectors. The pinouts and connectors vary from board to board. Every board has its own 5V regulator and it has to use big and clunky ATX power supply. Why not make single board solution, one regulator and get rid of the enormous PSU. Although it has big and fancy extruder daisy chaining network planned, the extruder requires point-to-point wiring to work, like what. And firmware.. the firmware. Original firmware is just awful. Poor performance and poor coding, sad, sad. I moved to Teacup firmware as fast as I could. And random routing problems too: it has non 45 degree traces, via and track sizes are more or less random and so on. Very amateurish.

Overview of my Mendel clone, featuring pieces from oak and polycarbonate

Unfortunately there isn't much better electronics out there. I made one 4x4cm version that had self made mosfet bridges to control 4 unipolar stepper motors and everything else needed for a 3d printer, but PCB order of the board failed and it doesn't seem useful so I ditched the idea. I have a plan to route 5x5cm board that has Atmega16u4 and 4 stepper controllers, but I havn't had the time yet.

Milled traces compared to TQFP44 package.

As I have failed from time to time in building a working extruder, I finally had it. I took my dremel and hotglued it to 3d printer. Little bit of playing later and yes, it can mill PCBs. The printer moves in 0.1mm steps. With the milling bit I have now I can make 0.4mm wide lines (clearance=0.4mm) and the smallest trace I could do is 0.1mm wide. Will try to mill some gerbers after re-routing Half Ohm PCB.

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Expanded mock up the satellite. SO-8 solar panel, QFN24 MCU, 0805 capacitor and two other passives.

Today I found a build of RF transmitter using one mosfet (and AVR). So, I started thinking. Say, we take the smallest solar panel we can find, like 22x7mm KXOB22-01X8-ND from DigiKey. Or CPC1822 in SO-8 package from Sparkfun. Then we add 3$ 0.4mm thick PCB from itead. On the other side, lets mount the most radiation resistant and low power MCU we can find - something from Texas Instruments MSP430F* FRAM series. The rest of the board space will be used for RF tranciver and tantalium capacitor. What we just got is a fully functional satellite with BOM cost less than 10$. If using SO-8 package the size of the entire satellite will be 6x5x3mm.

Why not start building it? I am still waiting Texas Instruments to come out with MCU that has FRAM and RF built in. FRAM is needed because it eliminates power consumption and makes it radiation hardened. Both necessary for space environment.

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Screenshot of Tech-thing KiCad Library editor

The KiCad default library is so messy. Sorting and editing everything with text editor is pain in the ass (atleast possible *hint at eagle*). I tried to download some existing library managers, but none of them worked. So... I made my own.

Tech-thing KiCad library manager manages both, the library files and module files. It lets browse all your library and module files and their content. You can delete and add files. Also delete, rename, copy and move their content. Supports library components with aliases, just use / between aliases (example: OPA334/OPA2334/OPA335/OPA2335). To use it, copy it to KiCad base folder and run it with python.

The code is made in python, using tkinter. I tried to make it readable and pretty but it ended up as always. At the moment it's at version 1.0 because it has all the functionality I wanted it to have, maybe sometime in the future, if there is an interest for it, I will continue developing it, but not this week.

Ideas:
v1.1 add file rename button
v1.2 make it easier to run on different operating systems
v1.3 refactor the code with askstring(...)
v1.4 make it possible to copy modules from board files
v1.5 add whole library viewer
v1.6 add search
v1.x maybe add more parameters to edit in each component (3d file location etc.)
v2.0 display pictures of each component

Download

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HP 4396A 100kHz-1.8GHz analyzer with HP 8504A 300kHz-3GHz s parameter test set

Some of the tested components

So I played around with some tools in Satellite laboratory. This time measured impedances of different electronic components. I used this weird network analyzer to generate signals and measure reflecting patterns. It plotted impedances on frequencies from 300kHz to 1.8GHz on its beautiful CRT display. I made pictures of two displays: Smith chart showing the impedance on different frequencies, and phase angle graph. The display was normalized on 50Ω load.

Smith chart shows the resistance on horizontal scale, and the reactance on vertical one. The line on the display shows impedance on different frequencies. If the line is above the centre line then the load is inductive. If it is below - capacitive. The middle point of the graph is 50Ω. Because ideal resistor is not reactive, it should be a dot on the middle line. Ideal reactive elements should be curves on the other graph (see the pictures).

1nF thick film capacitor, being pretty ideal in 10-20MHz range.

1nF thick film capacitor, on higher frequencies - an inductor...

Phase shift graph of 1nF film capacitor

10nF capacitor, looking like an induktor

Phase shift graph of 10nF ceramic capacitor

680Ω carbon resistor doing tricks

Self made coil, being what it should be - ugly

Phase shift diagram of the same coil

10uF aluminium electrolytic capacitor being a perfect inductor

Testing ferrite bead, the cheapest 0603 one from the farnell

Response from ferrite bead, i have no idea what it means

Coilcraft high frequency inductor - finally some near-perfect response

Tested component - Coilcraft 0906-2 RF inductor

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Charging of a capacitor

I always got puzzled when someone talked something about phase shift or something like this. From my simple view - if you plug the voltage in then there is voltage in. But, as it comes out - the current isn't. With simple resistor - the current is always proportional to the voltage, logical enough.

But with capacitor - if it is empty and you start charging it - it takes massive amount of current. When the voltage has reached to its maximum - the capacitor is full, so there is no current flowing anywhere. If we take the voltage away and connect it to ground, the current will also start from maximum and slowly approaches to zero. So, if we use a repeating pattern (like a sinusoidal wave) then there is an illusion that the current comes 90 degrees before voltage. So phase shift is 90 degrees.

Series inductor circuit.

With inductor, the same thing is a bit reversed. So, if we start with high voltage, the current is zero. And if we wait a bit, the current will climb up. After connecting it to the ground the current will start dropping slowly. And again, if we used repeating pattern, it would generate an phase shift. 90 degrees again, but, in another direction.

Using this knowledge, we can take some boring formulas and handful of resistors, capacitors and inductors to get whatever phase shift and series resistance we want. The complex number (two numbers in one) that we get from resistance and phase shift is impedance. It can be useful for describing passive circuits like filters. Also understanding this concept will help to understand how and why everything works in a weird way in high frequencies.

Capacitor and inductor in falstad circuit simulator. Inductor scope is the top one.

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Some time ago someone from the lab found userial - a USB to I2C/SPI/GPIO/ADC bridge (http://www.tty1.net/userial/). It seemed like an useful toy - USB to I2C and couple of IO's to play with. Basically connect it to your computer, fire up your HTerm and you can speak in I2C. But the cost of the chip used was enormous, so I changed the firmware to accept readily available atmega16u4. Couple of IO's and ADCs were lost during the process, but nothing really bad. The new firmware is here http://jaanus.tech-thing.org/img/userial-firmware-u4.tar.bz2

The hardware we use is atmega16U4 development board what you can find from Erik's page http://pro.a5d.biz/atmegaxxu4-development-board/ But it works with whatever hardware, so you can use it to test if your design works, without writing single line of code.

It was and will be again released under MIT license, it permits to share and modify it as you please.

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I have recently started spending a lot of time in University of Tartu Space Technology lab. RF boards in the trash box look so beautiful that I just had to make pictures. Since I don't know what all these boards to, the descriptions can contain errors.

Overview of the RF board.

Random inputs? and some filtering.

One of the big RF amplifier chips on the board.

The other RF amplifier, even bigger than previous one.

Output filter? or amplifier? The component is mounted on gigantic heatsink on the bottom of the board.

Power circuit of the board.

Old RF filter board.

Overview of the board.

Output part of some old RF board.

Middle section of the same board.

Input side.

Overview of 3G telephone mast PCB. Golden stripes show where the metal shielding connected to the board.

Golden bottom side of the same board.

Random

Probably some input filtering

Power supply of the telephone mast

Beefy amplifiers

Another switching regulator part

Awesome cascaded filters

Weird add on card, looks like magnetic-core memory

Some more magnetic-core memory

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Failed merging of gerbers

As studying electronics is mostly about trying and failing, I thought I should share some of my recent failures.

Most of the problems are fixable by point to point soldering

I merged 4 and 6 layer PCB orders for EstCube-1 satellite and added some of my own two layer boards to it. Unfortunately I managed to mess up the layers on two of them. One of the "fake" inner layers (all copper plane) ended up as bottom layer. The result: no tracks on bottom and whole row of components with all the pads on ground plane. The USB connector looks especially sad.

Other mistake: I confused the Cream and Solder mask layers. So as you can see from the picture - pinheads doesn't have solder mask clearance.

And then - Half Ohm board. For starters it had the same mistake, no tracks on bottom side. Fortunately there were nothing essential, so a little dremel and p2p soldering fixed it. But bigger mistakes were on the horizon. First - my schematic uses about 3mA, which, as I learnt is almost impossible to get out from CR1420 battery. Coin cells have unbelievably small maximum current and high internal resistance.

Pin-out of cheap op-amp

Pin-out of a expensive/precise op-amp

The second mistake - op-amp pin-out. As it turns out: even when using SOT-25 (SOT23-5) package, the pin-out differs from device to device. It would be reasonable to expect pin-out to be dependant on the manufacturer, but it isn't all manufacturers have the same pin-out. As it turns out the pin-out differs in cost. So all 0.2€ op-amps have one pin-out and all the 3€ ones have other one. So you can't design your product around cheap one and then upgrade it to better one. Argh, I hate it. Redesign of the whole board on the way.

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3x3x3 SMD led cube

Through the hole  LEDs are so big, that means that LED cube made out of them has to be big. But I want to make high resolution small LED cubes. So Kalle got an idea to use SMD LEDs. I soldered for couple of hours and made one. It consists of 27 red LEDs in 0603 package and 0.2mm copper wire. The side length of the cube is 3.3cm.

One layer of the cube powered up

It was really pain in the ass to make. I won't recommend doing SMD led cubes to anyone. This will probably be my first and last one..

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I bought an 17 inch ViewSonic VG712s LCD from local auction site. It didn't have an power adapter and there was no guarantee abut it working, but 10€ didn't seem much. After the arrival I read that it needs 12V@3.42A. Well, lucky me, I just happen to have 12V electrical system for my lab and an 12V 10A switching regulator powering it. After a bit of testing it came out that 12V means 12V, not 11.5V, had to make decent wiring to it to get rid of voltage drop. Because I try to power my 12V system from renewable energy sources when possible (I have 30W solar panel that powers it in the summer), it woult be nice to know how much power it draws and how it reacts to different states. So here is what I measured at 12V:

Lowest brightness, white screen: 1.662A

Lowest brightness, black screen: 1.768A

Highest brightness, white screen: 2.964A

Highest brightness, black screen: 3.051A

In sleep mode: 26mA

Turned off: 16mA

Couple of fun facts.. LCD takes less power with white screen on it.. weird. Also, there is no point of turning it off, because the difference is 10mA.. I guess that this power goes to powering the led on the front..

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Beautiful black PCBs from factory

ITead Studio and Seeed Studio are selling PCBs at so ridiculously low price that I just have to make new projects. I just got my PCBs. I panelized six PCBs on one 5x5cm ITead order and Cmc demanded pictures, so here they are. I went with black board with tented vias, just to see how awesome they would look. And awesome they are. The designs on the board are: the latest Kobold, tinyDino, three boards for Golem, my Robotex robot, and a RF board for Matis.

Cut the PCB with knife a couple of times

After breaking the border is a bit rough, try to align the cuts next time

At first I used dremel to cut the boards apart, but them Cmc told me to try to cut PCB with knife. Sound crazy enough to work. And after a little practice, it did work. It does require to cut several times from both sides, but it is order of magnitude cleaner and easier method than a dremel.

So, because my new design - Half Ohm, seemed ready enough, I ordered new PCBs. I used gerbmerge to panellize, because the Half Ohm is designed in KiCad and the other design I share board with - in EagleCad. After a small fight with conf files my gerbers were merged.

Design after merging with gerbmerge

And going to SMD really takes down the holecount on boards. Normal THT boards require 1 hole per leg. My last design has 74x 0.4mm vias for signal, while it has 100 component pads (not counting passives), also interesting is that I put 100 GND vias on 10x10cm board, that sounds much but one via per square centimeter isn't much at all, especially for medium power designs.

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Cable after shorting

I tested my reprap and managed to short something out. I didn't notice it first but after a couple of seconds I saw smoke coming from under my table. The wire connecting my power supply and power system had almost liquefied and was giving out tons of smoke. I unplugged it and it stopped.

My other power source - the battery, had 10A one what went out right away. Next job - make sure that every power wire is fused. The lesson for today - use fuses. There is never enough of them! Next time when making a project, add some. And if you want to protect ICs then self resettable fuses/PTCs.

Mini-Blade fuses after blowing

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This is a follow up to my last post.

A test equipment is worth nothing if you don't know if you should trust it. Only way to trust it yourself of convince someone else to trust it is to calculate the error properly. So I will show a simple example of error calculations by calculating my Half Ohm error. The rules of thumb for error calculation are: To calculate error of adding and subtraction take the bigger error. To calculate error of multiplication or division - add errors. So if you have 1% and 10% resistor in series their resistances add up. So their combined error is 10%. To get voltage divider error you have to add errors of resistors and input voltage.

Meanwhile I learnt what are chopper/zero drift amplifiers. Before, most of the error was from op-amp input offset voltage, but zero drift amplifiers have about 1000 times smaller input offset voltage for the same money. From that point of view I changed all resistors to 0.1% ones and recalculated their values.

To calculate error of a circuit we have to first know the formula of the circuit. Simplified formula of my circuit is  (V_in*x/R₁)*gain. So I have to calculate the error of each part and add them together. The first place where the voltage enters is voltage reference. The voltage reference is 0.5% precise. Next was the divider resistor, that is also 0.1%. So the total error is 0.5% + 0.1% = 0.6%.

Next error comes from the voltage divider. Output voltage is  V_in / (R₁ + R₂) * R₂ where V_in = 1.24V, R₁ is divider resistor and R₂ is the resistance we are measuring. But because we presume that the output is linear, we can think that V_out = (V_in / R₁) * R₂. This is acceptable if the R₁ is order of magnitudes higher value than R₂. The error is the bigger the bigger is R₁ resistance. So worst case scenario is when measuring biggest resistance. But on the other hand, the smaller the R1 the smaller error from op-amp input offset voltage. I calculated with some resistors in spreadsheet and settled with 620Ω resistor. It offers almost minimal combined error of 0.41% and the gain of the op-amp has to be exactly 500, what is easier to achieve than lets say, a gain of  403.225806451613.

Both of the resistors for the op-amp give additional 0.1% error. So the grand total worst case error will be 0.6% + 0.41% + 0.2% = 1.21%. And each Ohm of resistance in test probes will give additional 0.16% of error.

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Voltage divider to measure unknown low voltage

I watched EEVblog's video about debugging a short circuit with precise multimeter. He determined the direction of shorted place by comparing resistances in different places. I wanted to debug like that too and also measure resistances of wires and connectors, but all cheap multimeters measure only down to 0.1Ω. To get 10mΩ I have to buy 400€ multimeter. So I searched and found an article describing cheap and dirty way to measure low resistances. You need a known voltage source and known resistors and then you can form a voltage divider and measure the resistance. Awesome! But the form factor and all the math behind it sucks, as a plug and play device it would be perfect. I though about making it its own box, but was almost impossible to find cheap probe connectors for panel or PCB. So it will be a one PCB product.

First, the concept.

• It should measure resistances from 1Ω to 0.1mΩ
• General purpose - can be plugged in any multimeter.
• Output should be in mV, because most multimeters have mV display.
• No math, so 1mΩ is translated to 1mV and user doesn't have to calculate anything.
• Precise enough - 1% is nice number, but it's not very important, as usually we need the resolution, not the absolute precision.

Secondly the schematic. It is fairly simple: power supply -> voltage reference -> current limiting resistor -> connector for test probes -> voltage amplifier -> amplifier do to the math -> connector to multimeter.

BR1225 voltage curve with 330Ω/9mA load

It will be using small 3V coin battery as power supply. I though about the schematic and BR1225 coin cell would be perfect size and I already have 30 of those. Maximum urrent consumption will be about 10mA so I checked how much voltage I will get out of 3V BR1225 @10mA. The voltage started out from 2.5V and dropped to ~2.1V, then it stayed there. So our power supply gives out voltages between 2V and 3V. Edit: From there we can calculate that the internal resistance of the battery is (3V*330Ω)/2V - 330Ω = 165Ω.

Low ohm measurement schematic

The higher the reference voltage, the less error from amplifier, but too high voltages and currents can damage schematics, so we have to mind that. Less current means more error from amplifier, but higher current - more error from test leads and connectors. So I started to search cheap voltage reference below 2V. The highest voltage I found was 1.24V. I chose 1% shunt reference with up to 20mA current handling. The resistor between voltage reference and battery should limit the current so that with maximum voltage of 3V the current will be smaller than 20mA. So the value of the resistor has to be at least (3V-1.24V)/20mA = 88Ω. The nearest round value that I like is 100Ω, so I will go with that.

Next, the resistor. The shunt and current limiting resistor in parallel with it form a current divider. The value of measuring resistor should be chosen so that with minimum battery voltage, still at least 1mA of current flowing through the voltage reference. There is (2V-1.24V)/100Ω = 7.6mA of current flowing through the voltage reference and resistor. 1mA to voltage reference and we get that the resistor has to be 1.24V/6.6mA = 188Ω. I think that I will go with rounder 200Ω.

Positive feedback amplifier with gain of 161

The amplifier will be configured in positive feedback mode. When measuring 0.1Ω resistor, the output must be 0.1V. The gain must be: 0.1V / ((1.24V/(200Ω+0.1Ω))*0.1Ω) = 161. Since no common resistor values divide by 161 then the easiest way to get gain like this is to use 1k resistor and 160k resistor in parallel with another 1k resistor. Edit: Since I suck at math I wrote that wrong. The gain of the op-amp is (R₁+R₂)/R₁. So I need 1k for R₁ and 160k for R₂.

Okay, all this seems pretty on paper, but will it work? Next post will be on error calculations to find out how precise the beast is.

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Qt4 grass physics engine

I got a little bored when visiting my parents and last place I tried to go to work didn't want me because of my poor C++ skills. So best way to practice OOP in C++ and familiarise myself with the syntax is to make a project. My idea of project - a 2d physics engine for grass... It had GUI, OOP and was simple enough for one evening project.

I found very good tutorial from site http://zetcode.com/tutorials/qt4tutorial/ . Surprisingly GUI programming in C++ was exactly the same as in Java or in Python. The C++ syntax was easy too because I had seen it for years, and finally I understood why it was like that all along. Also qmake is very useful, must learn that more.

Secondly I realised (again) that random function is very useful in games, and more or less useless in everything else. And finally - the GUI worked at 100FPS, I love fast reacting GUI. Damn shame that my computer is slow/Intel Atom.

Source/binary: http://jaanus.tech-thing.org/img/c++_qt_test.tar.gz

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Cheap (and fake) usb hub from ebay.

So I needed USB hub for my robot. So I bought one from eBay. When it arrived I started to test it, because, well, i don't trust eBay. It worked well when connecting one device, but stopped working with multiple devices.

Fake USB hub taken apart

After testing it a bit i decided to take it apart. The insides looked a bit suspicious - there were no crystal and one pad for crystal was connected to ground. I decided not to waste more time on it.

No chip inside, only tracks.

But then! Kalle appeared and took the piece of glue away with reworking station. And all the fakeness was revealed. It didn't have any chip inside, only tracks. And USB husbs must always have some chip inside that deals with all the traffic. This one worked as a junction box - if you connected one thing then it worked, if several - they shorted each other out.

But whatever. I'm not unhappy, I got cool box and bunch of connectors for 1.8$, but all you, who need a real hub, don't buy it. I bought it from shop named gogo21shop.

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