Feb 022014

Cheap laser pointers abound in many different products. I recently purchased a handheld infrared thermometer and it included a red laser pointer for sighting purposes. The first thing my mother asked was, “Is it dangerous?” to which I replied the standard “no” but how can I be so sure?

GM550 IR thermometer

According to the product markings it uses a “safe” Cat II laser. It also had markings for CE and FDA approval but then again it was a cheap product made in China.

I had a quick search online for how to check laser pointer safety but drew a blank for low-power red laser pointers. I did on the other hand find a useful academic paper written in fairly accessible language identifying concerns and how to check green laser pointer safety. It may be worth a read to check whether any of the concerns raised and methods used could be relevant to red laser pointers.



An inexpensive green laser pointer was found to emit 20 mW of infrared radiation during normal use. This is potentially a serious hazard that would not be noticed by most users of such pointers. We find that the problem derives from an unsafe design, and describe a simple method of testing for it using common household items.

 Posted by at 7:12 pm
Feb 012014

This week I bought a cheap GM550 Infrared Thermometer on eBay. There were many models to choose from but this one appealed to me due to its low price (GBP 11.35) and stated measurement range (-50 to 550 C). Other cheaper units exist but they have a lower maximum temperature (typically 380 C) which may not be adequate if I need to measure stove and incinerator temperatures.

The GM550 thermometer has a resolution of 0.1 C and claimed accuracy as follows:

 0 C to 550 C +/- 1.5 C or +/- 1.5%

-50 C to 0 C +/- 3 C

* Whichever is greater

According to the specification, normal room temperatures should be measured to about +/- 1.5 C. Temperatures below freezing are much less accurate (+/- 3C) and the highest temperatures should be within +/- 8.25 C.

I have compared room temperature readings taken with the GM550 and an Oregon Scientific digital thermometer (a domestic thermometer) and found the readings to be very similar, typically within 0.8 C.

The GM550_User_Guide was written in surprisingly good English and was easy to understand. It explains that this thermometer has a preset emissivity value (0.95) and that shiny and polished surfaces must be covered with masking tape or flat black paint before readings are taken.

The GM550 looks and feels very well made and appears to function well. The LCD screen is bright and easy to read, and the unit casing is made from rigid plastic that does not flex under normal use. The thermometer fills your hand and has gives the impression of being a good quality device. If you want a cheap non-contact digital thermometer with a wide temperature range then this unit may well be suitable.

Jan 012014

I finally got around to trying out my ENC28J60 Ethernet adapter with an Arduino micro-controller. These adapters are very cheap (about 2 GBP on eBay) but are frequently considered difficult to use compared with a “standard” Arduino Ethernet shield.

I connected the ENC28J60 adapter to an external 3.3V power supply (with common ground) and measured the current draw at about 108 mA. In case it is not clear, this measurement confirms the ENC28J60 draws too much current to be powered by the Arduino 3.3V pin.

I downloaded the Ethercard library which provided some simple examples to create a web browser, test DHCP, etc. So far, these have all worked as expected and the card has proven much easier to use than I had initially supposed.

I have been playing about with email access for the Arduino which involves a simple PHP script that I have posted online. This allows the Arduino to request the page and thereby send an email. This could be used to send an alert or some data by email.

Dec 302013

I’m sharing this instruction book (with circuit drawing / schematic) for the Farnell L-Series Bench Power Supplies in case it is of use to anyone. These bench power supplies are frequently available on eBay (e.g. Farnell LT-300T dual power supply 0-30V 0-2A) but they are old, probably dating back to the 1970s.


Example model numbers:

  • Farnell LT-300T
  • Farnell LT-301
  • Farnell LT-302

Download the instruction manual: Farnell L-Series PSU

Oct 202013

I bought one of these pressure sensor breakout boards from a Chinese supplier on eBay.

GY-65 BMP085 pressure sensor

The board has a BMP085 barometric sensor, 662K voltage regulator (3.3 volts) and two 4.7K resistors. It has three other components that I have not identified. I presume the resistors act as pull-ups on the SDA and SCL lines for connection to the I2C bus.

I have tested the breakout board using 3.3V and 5V power supplies. I used an Arduino sketch to scan the I2C bus and found the pressure sensor at 0×77. I tried the Adafruit BMP085 driver and it appeared to function correctly.

  • VCC – 3V3 or 5V
  • SDA – Arduino analog 4
  • SCL – Arduino analog 5
  • XCLR – (no connection)
  • EOC – (no connection)
  • GND – ground

GY-65 BMP085 pressure sensors are available on eBay for less than 3 GBP including delivery.


Oct 182013

I bought three EM-152 stepper motors for use in a small project that will eventually have an X-Y-Z table. By examination and testing I have found the following information:

  • motor type = 5-wire unipolar stepper motor
  • step angle = 3.75 degrees
  • steps per revolution = 96
  • resistance = 52 ohms



Oct 032013

I just installed Ubuntu One and found that it crashed every time it was launched. For reference I am using Ubuntu 12.04 LTS and the error message was “IPC Error”.

Fortunately there is a very easy fix for this problem. All I had to do was create this file and then restart the program:


The config file now contains the following info:

autoconnect = True
share_autosubscribe = False
udf_autosubscribe = False

show_all_notifications = True

read_limit = -1
write_limit = -1
on = False
Oct 012013

I use Gnome Classic desktop on Ubuntu 12.04 LTS (64-bit) and the Alt+Tab keyboard shortcut was not working as expected: it did not switch windows. The following notes show how I fixed it.

  • sudo apt-get install compizconfig-settings-manager
  • System Tools > Preferences > CompizConfig Settings Manager
  • Category > Window Management
  • Static application switcher (selected)


Sep 242013

These step-by-step instructions show you how to add an application (program) shortcut to the panel (toolbar) on a computer running Ubuntu with the Gnome desktop environment.

Press Windows + Alt


and then right-click the panel. Select Add to Panel…

Add application to Gnome panel

If you want to copy an application shortcut that is already in the menu, select Application Launcher… and then click Forward.


Browse for the required application shortcut and then click Add.


The shortcut should then appear on the Panel.