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CPU Gauge

An analog gauge with USB, serial and analog interface.

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The idea is simple. The project aims to create an old style analog gauge you often find in a car or motorcycle. Out of the box, when plugged into an USB port it would display CPU usage (some drivers on the host would be also required) or other quantity like network or memory usage. For some curious users I plan to include an API which would enable them to interact with the device from their programs. For hackers who would want to plug the gizmo into Arduino or other development board I'll include simple serial input (and maybe even analog).

This is my first project that is cost-optimized and if I succeed with the prototype, I'll try to sell the thingy.

The device uses a micro stepper motor which has enough torque to move lightweight needle. Although the motor has only 20 steps, experiments with extensive micro-stepping gave satisfactory results.

  • "Flex" PCB and unusual motor

    lukasz.iwaszkiewicz02/04/2015 at 09:04 2 comments

    I just added a photo of simple and small PCBs which will act as a connector between the main PCB (main board sounds cooler) and the motor. As I stated earlier (or maybe I forgot) there are special (geared?) stepper motors for driving such things as tachometers, or other gauges in automotive industry. Just type "switec" in Google images and you'll get the idea. The problem is, that they are relatively expensive (few $) and relatively big. So my idea was to use those tiny motors you'll find on my photos, which I've got from China. I have no Idea what was their original purpose, but they suits me pretty well. This is a hack you might say, but well, we are on "hackaday" right?

    To the point - I'll try to connect the motor and the PCB using another, tiny PCB (0.3mm == 12mils thick). Main board has a special slot (chink, crack? what is the proper word?). And the tiny ones, at one side have holes, like THT ones which will suit for the motor terminals, and the other side they will slide into the hole on the main board and the pads will be soldered together. I've seen such connections on few boards in the past, so hopefully I'll get nice working and nice looking results.

  • Still alive

    lukasz.iwaszkiewicz02/01/2015 at 20:12 0 comments

    Certainly still alive, because it is my most polished project to date. Recently Rev 4 boards arrived from China, and they look great. In the meantime I am working on the oven, so I could bake some bigger quantities on my own (my aim, and big dream is for 100 pcs of this, but this will depend on the interest from the public - I didn't made a webpage though. Ha ha BTW my initial plan and New Years resolution was to sell ONE to somebody). So for now, the oven is slowing me down (to little power).

  • Stepper motor non-linearity

    lukasz.iwaszkiewicz11/30/2014 at 22:49 0 comments

    Here's the plot showing angle change over time. I put sin on the one winding and cos on the other, and motor spins as expected, but also a little trembling is noticeable. It is as if on every step needle slowed down a little bit. The effect is, that the movement is not smooth as I like it to be. I tried to modify my sin and cos tables, but with no luck. So I used some rotary encoder and measured the angle over time in hope that this information will allow me to somehow modify my arrays and correct the error (this non-linearity is caused by the shape of the rotor and stator I believe).

  • Oscillator fail

    lukasz.iwaszkiewicz11/05/2014 at 10:22 0 comments

    Although firmware has proven to be fairly reliable i.e. it successfully communicated with the host, it worked properly only when run on the MSP430F5529 evaluation-kit. When uploaded to the target device (depicted somewhere on the photo on the far left) it would not make the device to enumerate, and there is no sign of an USB communication whatsoever (other than that, the firmware runs). The whole pull-up resistor thing that I described earlier didn't help, so after debugging further I discovered fatal mistake I made : I mixed up the XT1 and XT2 oscillator inputs :( So for now I have board which would feed RTC with 4MHz signal (if I only used the RTC), and has main oscillator without a crystal. Will try to feed the clock signal in "bypass-mode" directly from a generator when I only get back home.

  • D+ pull-up missing

    lukasz.iwaszkiewicz11/03/2014 at 21:51 0 comments

    I finally uploaded (some say "downloaded") the firmware into my device and it seems that host does not see it. I found an error on my schematic which caused this : there was no 1.5kΩ pull up resistor metween PUR pin and D+ pin. Every USB host has 15kΩ pull down resistors built in on D+ and D- rails, and when noting is connected to the port both lines are low thanks to that. On the other hand, full speed USB devices have 1.5kΩ pull up resistor on D+ line which "wins" over the host one (15k) and when connected, the D+ goes up. This information tells the host that something was connected and what speed it is. As far as I remember neither STM32's nor TIVA-C ARM µCs didn't require those external pull-ups (they must have them integrated), so it came as a surprise to me. Now it's time for some quick and dirty fix.

  • New layout

    lukasz.iwaszkiewicz10/27/2014 at 08:49 0 comments

    I was disappointed by the USB connector etched directly on the PCB. It turned out, that PCB must have been approx. 2.5mm thick to hold the device in it's place in the USB socket (I glued 3 layers of thin plastic which can be seen on the photos). So I decided to include "true" USB A connector after finding that they aren't so expensive.

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Discussions

Phil.sydor wrote 02/07/2015 at 14:02 point

Great project and your boards look good too! How have you solved the needle going to zero on startup problem?

  Are you sure? yes | no

lukasz.iwaszkiewicz wrote 02/07/2015 at 17:43 point

Thanks! I don't know if I understand the question correctly. When unpowered, the needle stays in one of 5 discrete positions (because this is a 20 step motor, and the rotor has 5 teeth - as far as I can tell). When you power it on, the firmware will move the needle all the way to the right, and then back to the left (kind of calibration), where needle will stop on the little bumper (goldpin to be precise). My motorcycle does so (i mean this calibration), so I think this is right way to do.

  Are you sure? yes | no

Phil.sydor wrote 02/07/2015 at 18:39 point

Thanks for your answer - that makes sense . If the gauge is turned off in positions 1 to 4 the needle hub will then slip when the needle hits against the bumper , is that correct?

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lukasz.iwaszkiewicz wrote 02/07/2015 at 20:03 point

Yes. When you power off the device (i.e. switching off the computer it is attached to), the needle will jump (instantly) to the position where attraction between rotor tooth and the stator is the strongest.

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Dimitar wrote 02/07/2015 at 12:33 point

Very good project Lukasz, how can I buy several of these assembled ?

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lukasz.iwaszkiewicz wrote 02/07/2015 at 15:23 point

Thanks! The project is under heavy development and I plan to start selling the thing but not just yet, but in month or two. I fixed all the issues with the PCB and mechanical part, but now I must polish the firmware and software, then perform extensive tests, etc. There are whole lot of things when making a commercial product rather than prototype for your own use.... I'll definitely keep you all informed.

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crowe.gabriel wrote 02/05/2015 at 16:20 point

I would buy this, if it went all the way to 11.

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lukasz.iwaszkiewicz wrote 02/05/2015 at 16:26 point

Haha :D It can spin 360° - it depends on the firmware / host software which aren't ready yet :D Besides I made 4 holes in the PCB so potential user could solder (or desolder) a single goldpin which would stop the needle. But without this goldpin, the needle can go continuously around.

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Audrey Robinel wrote 02/05/2015 at 13:57 point

This is a pretty neat idea, and a really nice realisation!

I however wonder why a stepper motor rather than a small servo?

  Are you sure? yes | no

lukasz.iwaszkiewicz wrote 02/05/2015 at 14:04 point

Simply because I found those motors online, and they are super small and super tiny (like 1cm tall and 0.5cm wide) and I was wondering if I could make a gauge out of them. Started as a experiment, and turned into something bigger. Also I always thought that those SWITEC motors you can find everywhere are some kind of geared stepper motors, but now I'm not sure :D

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