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The USB Microscope, for PCB Development : A Review

Introduction

100080For a few years now the death of the Plated Through Hole (PTH) component has been wrongly predicted and hobbyists are still able to dabble in electronics, using PTH components, without finding ingenious ways to mount Surface Mount Technology (SMT) components by hand.

However, although PTH components are still readily available, there is a strong demand for the hobbyist to use SMT components due to space constraints. This is because in modern day DIY hobbyist electronics the design area, the prototyping area the hobbyist has to experiment in, is becoming increasingly smaller than what has been available previously. This in turn is dictating the size of components that can be used. 

When SMT components are required, although a magnifying glass is helpful, a truer friend than the USB microscope may not be found as we attempt to find out in this review. 

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Figure 1: If you don't own a dog owning a USB microscope could be your next best chance of having a true friend.

USB Digital Microscope  with 400x Magnification

The first task when deciding to use a USB microscope is choosing which one to buy.  This can be quite difficult as there are a myriad of USB microscopes on the market to chose from, with most being offered at modest prices. However, since some of our project work is performed on the Chrubuntu LINUX (a variant of Ubuntu for Chromebooks) platform, when choosing, it was essential to find one that works on the LINUX platform in general and with Ubuntu  in particular.

However, quite ironically, the USB microscope we decided to use seen, in the Figure 2, below had been purchased a while ago and clearly stated that it was intended for use on the different flavours of the MS Windows operating system, upto to Windows 7. Although reading this seemed quite worrying, an Internet search suggested that most USB microscopes are treated like a webcam and using one on LINUX should not be a plug and pray process. 

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Figure 2: USB microscope purchased from Maplin. Nice isn't it! One of the good things about this one are the magnification markings on the magnification dial. There is also a dial to adjust the brightness of the LEDs or switching them off completely.

Bearing this in mind and since LINUX is more of a plug and play OS, compared to its declining plug and pray rival, using any capture software like the recommended Cheese Photo Booth should work. Hence we were quite excited to use the microscope, purchased from Maplins, which was quite well packaged incorporating a mini CD with driver software and utilities for MS Windows. 

If the blurb on the packaging was to be believed then the microscope's 1.3 Mega Pixel (MP) CMOS camera would treat us to images with a maximum capture resolution of 1600 x 1200 pixels, in glorious 24-bit RGB colour. It also promised a magnification ratio of 20x - 400x with a shutter speed of 1/1000 to 1 sec. Also, promisingly, 8 white LEDs would help illuminate our subject matter at a frame rate of <30fps@600 Lux, which would be transferable to a USB 2.0 compatible host.

Since our primary aim of using an USB microscope is for nothing more than inspecting our DIY PCBs the blurb impressed us as much as a clown is impressed by seeing someone with oversized feet!  It didn't mean very much to us at all, just a set of numbers. The proof will be in the pudding when we start using it to analyse our PCBs! 

Just Say Cheese

To test the microscope it was plugged into one of a Chrubuntu (LTS 12.04) Chromebook's USB ports and the command 'lsusb' was typed in a command window. The result as can be seen, in Figure 3, below, suggests that the microscope is manufactured by Z-star Microelectronics. To ensure that the correct device has been identified it was plugged and unplugged a few times with lsusb producing the same result of listing or not listing the Z-Star entry,  on each occasion.

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Figure 3:The last entry of the listed USB devices in this image identifies the USB microscope as the device 0ac8:3610 registered to Z-Star Microelectronics Corp.

The next step we took was to install the Chesse Photo Booth application from the Ubuntu software centre, alternatively we could have installed the application by typing the command 'sudo apt-get install cheese' in a command window.  Once this was done and Cheese was successfully installed, it was fired up and we promptly saw an image of ourselves in a display window on the Chromebook. After turning our head from side to side, inspecting and not liking either side's profile, captured by the Chromebook's webcam, we though it was time to get back to business and find out how to set Cheese's to acquire images from the USB microscope and not the Chromebook's webcam.

Although we couldn't find a way of setting the system wide default capture device to the USB microscope we could, in the Cheese application, set the capture input to the Vimicro USB 2.0 Microscope as can be seen, in  Figure 4, below. This provided us with images with a resolution of 640 x 480 pixels, which is much less than the advertised 1600 x 1200 pixels. We haven't explored any of the other settings, which may allow us to increase the microscope's resolution or image quality.

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Figure 4: The preferences dialog of Cheese Photo Booth set to acquire data at a resolution of 640 x 480 pixels.

Results

Some images acquired during the assembly of one of our prototype PCBs can be seen in the following Figures.

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Figure 5: A close-up of the hand-soldered, but not yet cleaned, 4-bit voltage level translator. 

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Figure 6: The USB microscope is extremely useful in visually inspecting signal traces. In this image the microscope has enabled us to pinpoint the exact location of the discontinuity of the signal traces not readily seen by the naked eye.

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Figure 7: A potential short-circuit has been spotted and removed in this photograph. If this short-circuit had not been spotted and removed it could have been quite disastrous as it would have been difficult to locate as, as can be seen highlighted in the image, it is underneath the SMT component.

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Figure 8: The USB microscope has been used to confirm the alignment of this hand-soldered SMT component, which measures approximately 3 mm by 4 mm.

Conclusion

We paid what could be considered a premium for a Maplin branded USB microscope and it has been worth every extra penny spent.  This is a rock solid device with no noticeable drift in magnification, which, quite irritatingly, affects the focus of some of the cheaper variants. As an aid in assembling DIY PCBs this is a great tool to have for many different PCB assembly tasks including visual signal trace continuity inspection, device alignment and for checking for short circuits after soldering.

One of the limitations of using this device on the LINUX platform is the lack of accessibility to some the utility functions available on MS Windows platform. However, any veteran LINUX user is used to this lack of comparable support and  we didn't feel we needed to use any utility functions during our tests anyway.

Compared to an unbranded USB microscope, we have used previously, we really like this one. Although there is a strong suggestions that many, if not most, of these devices may be manufactured in the same factory in China their individual performances differ quite considerably. When considering purchasing one, it is worth shopping around and spending that little bit extra, because as we found with this one all USB microscopes may be equal but some may be more equal than others.

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