A collection of computer systems and programming tips that you may find useful.
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Thursday, September 29, 2016

pi_power - power management for portable Raspberry Pi projects

I have been working on a portable Raspberry Pi project for a while - still not there yet but I've completed one important piece.

It's portable so it obviously has a battery. The Pi takes quite a bit of power so it needed to be rechargeable and include a charger. Adafruit make a great device called the PowerBoost 1000C which takes care of the core charging and power supply functions. But I really wanted my project to work like my phone does:

  • To power it up from a cold state, press a button for a few seconds
  • To power it off, press the same button for a few seconds
  • Indicate how much power remains in the battery
  • Provide an alert when that is running really low
  • Shut down safely without any data corruption if the battery does run out
  • To recharge the battery, just plug in a cable from a USB charger

  • I couldn't find anything that provided all the functionality I wanted - so I built my own

    pi_power consists of fairly straightforward circuitry that links the PowerBoost to the Pi in conjunction with two python scripts that run in the background and monitor the battery voltage.

    If you are building a portable RasPi project then you might want to take a look

    Wednesday, June 8, 2016

    Image capture software for cheap USB microscopes

    Look on Amazon and you will find a variety of cheap USB microscopes. These are basically a USB video camera with a macro lens. They are good for inspecting fine details of things like electronic components, plants, insects, stamps, etc. but they are not powerful enough for looking at, say, cells in biological samples.

    I just bought one to help me capture images of various plant pathologies.

    They are marketed as having a range of magnification from, for example, 20 to 300X and the cameras have resolutions anywhere from 0.3 to 5 M pixels. Be aware that the specified magnification range may include the magnification inherent in displaying the image on a large monitor !

    Dino-Lite make a range of professional USB microscopes of various sorts but these can cost hundreds of dollars. For basic experimentation there are a load of other vendors and products with prices in the $50 - $100 range.

    If you look on Amazon it will be obvious that the same basic models are being sold be several different vendors.

    Here is the one that I bought for $60 which is branded  DBPOWER

    The same microscope with the same stand is also branded as :

    Celestron 5 MP Handheld Digital Microscope Pro  $83

    And with a different stand, or without a stand, by a wide variety of other vendors

    I went with the $60 DBPOWER variant with a 5 MP camera. It comes with the stand in two pieces and a CD containing software called MicroCapturePro for PC and Mac.

    You need software to interact with it - it does not just show up as a camera in the MacOS ImageCapture or Preview tools.

    I don't have a CD drive on the machine I want to use this with and transferring the software from one that does is a bit of a pain. So I looked online for the software.

    You can get MicroCapturePro from Celestron but after digging around a bit I would recommend a different solution.

    Plugable have a similar microscope and they provide a piece of software called Digital Viewer - get that and install it on your Mac (they have a Windows version too). When I started it up it displayed the view from my webcam but click the Settings icon in the top left and select the microscope.

    The focussing mechanism on these microscopes is a bit rough but you'll get used to it. I can see that I may want to build myself a better stand and illumination rig.

    Under Settings you can select the image resolution and do a bit of image adjustment. You can take individual images, videos or a set of timed images.

    It looks like it will do exactly what I need it to do - for $60 that's not bad.

    Here is an example image:

    Thursday, January 28, 2016

    Raspberry Pi - strange icon in top right of screen

    I have been working with a mobile Raspberry Pi project powered by a LiPo battery and a Powerboost 1000c charger from Adafruit to handle battery charging.

    Several times I have seen a small square icon in the top right of the attached small HDMI screen that has a rainbow of colors. I had absolutely no idea where this came from or what it represented.

    But now I do... https://www.raspberrypi.org/forums/viewtopic.php?t=82373

    The B+ (and presumably later models) has an under-voltage trigger that shows itself as this 'rainbow' square in the top right of the display when the supply voltage drops below 4.65V.

    In addition, an over-temperature trigger displays a solid red square in the same location if the temperature goes above 85deg C.

    You can disable the warnings in config.txt - see the link for details

    I'm glad that the system has these triggers but I don't think the display of a red/rainbow square is a good way to inform the user.

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