Incredible 6 parts CNC plotter

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Jay made the smallest CNC plotter made by Laser cut parts which according to his blog cost about $20 to re-produce, this is really amazing piece of engineering:

http://plotterbot.com/2013/11/how-to-build-a-tiny-cnc-drawing-robot/

I do wonder if something similar could be adapted for solder paste syringe and to make small solder paste spit machine which to eliminate the need for stencils for prototype runs.

Experimenting with low power modes and Arduino

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Tero Koskinen recently did interesting experiments exploring how low power he can go with Arduino. http://arduino.ada-language.com/saving-power-with-avr-ada.html

He made setup with 5 boards to test:

  • original Arduino Duemilanove
  • original Arduino UNO
  • Olimexino-328 clone
  • Arduino DIY PTH kit from Sparkfun
  • Diavolino from Evil Mad Scientist

He correctly shut down all not used peripherials, Brown-Out-Detection, slowed down the CPU speed and used Power Saving modes.

the results were:

Device Current
Duemilanove 7.50mA
UNOr3 18.10mA
Olimexino-328 4.00mA
Sparkfun PTH Kit 7.60mA
Diavolino 0.50mA

 

Diavolino have nothing but the AVR so obviously is winner with this setup with only 0.5mA consumption.

Wait if there is no power regulator where these 0.5mA go when AVR is put in low power mode?

Looking at the schematic  you can see R1 RESET pullup 10K resistor which is connected to 5V -> 5V/10K = 0.5mA the whole consumption is taken by R1!!!

 

Then let’s see OLIMEXINO-328 the second place with 4mA (outch!) this board is promoted by OLIMEX as SUPER DUPER LOW POWER BOARD then why these bad results? Where these  4mA go?

The answer is obvious: Tero is powering OLIMEXINO-328 by the POWER JACK.

In our design we assume if the power come from the power jack it’s unlimited and we can waste it as much as we need – charging Lipo (if attached) etc.

So these 4mA are taken from the DCDC in the input.

If Tero wanted to see how OLIMEXINO-328 shines in low power he should have powered the board by the battery connector. When the power is applied to battery OLIMEXINO-328 is very humble and will need less 20 micro ampers 0.02 mA to operate!

How this is done? If we look at the schematic we will see that there is no RESET pull-up, but the RESET is done by tricky circuit with R12/R13/SD5/C7/C8 this schematic have zero consumption but still perform RESET functionality.

Also unltra-low-power LDO which needs just 3 micro amps to operate MCP1700T-3302E/MB is used for power regulator.

This makes possible complete Arduino to may keep working while consuming less 20 micro amps.

What 20 micro amps consumption means? If you use our standard LiPo 1400 mAh battery your board can work 70 000 hours or 3 years!

The other boards: Sparkfun kit 7.6 mA, Duemilanove 7.5mA and UNO 18.1 mA just use cheap voltage regulators which take this current, but it’s OK they have not been designed to be low power.

What is the conclusion: with right setup (powering from battery) OLIMEXINO-328 is the lowest power Arduino solution on the market! When we add to the low power the industrial temperature operation range -25+85C and the possibility to work with any input voltages from 9 to 30VDC, OLIMEXINO-328 is the most sophisticated board with many features while keeping the price reasonable.

Low Cost LCD-TO-VGA adapter

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A13 processor have no HDMI and VGA output as his big brother A10, so we had to work out something using the LCD interface it have.

We browsed IC video DACs and there is plenty of them, but they are expensive and didn’t fit well OLinuXino low cost concept, so we decided to give a try and make simple R ladder video DAC.

A13 LCD interface is 18 bit this means we will need 3 channels x 6 bit Video DAC.

All VGA monitors have 75 ohm terminator on their input lines and the video signal is 0.75V for white level and 0V for black. So knowing this we could make resistor ladder DAC with R, 2R, 4R, 8R, 16R, 32R connected in parallel with RGB 0-5 bits. The values are easy to calculate when we know the LCD buffer output voltage 3.3V and the voltage we want to have when all bits are “1” i.e. 0.75V. The resistors using the 1% precission values picked were 549 ohm, 1050 ohm, 2180 ohm, 4370 ohm, 8660 ohm, 17800 ohm.

The adapter was routed and pcb prototypes were run. The assembled adapter was attached to LPC1788 board with 4.3″LCD with tweaking the output to match VGA lock frequency and the result was perfect.

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The picture which appears on LCD was color stripes with small ball which you can move by tilting the board (using on-board accelerometer), as you can see from the picture the colors are perfect and image is standing still with no glitches and jitters.

So now we have low cost VGA solution for our A13-OLinuXino and can move forward with the PCB schematic finish and routing. Note that the VGA signals go through buffers which are gated i.e. we can enable and disable the VGA output and A13-OLinuXino will be able to work with both LCDs and VGA.

EDIT: schematic is included here below:

iMX233-OLinuXino-Micro the EUR 20 Linux single board computer is routed nice and clean

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We finished the iMX233-OLinuXino-Micro routing and the files are push to GitHub.

Tomorrow we will run the prototypes, we were very tempted to see if we can make the design 2 layers first, we placed the memory directly under the iMX233 processor so the signal paths are very short and should be not problem for 133 Mhz, but the cross talk may play bad joke for us with no ground planes to separate the signals. Well crossing fingers and … we’ll see in few days on what frequency it will run.

Meantime the software developers did enormous amount of work. The iMX233-OLinuXino have now Open Embedded Layer and Raivis now is having fun with Linux Kernel 3.3 trying to move the 2.6.x drivers to the latest Kernel.

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