Wednesday 6 June 2012

A year of developments

After returning home from almost a year away on a work assignment I now have a little time to continue with my BlueFlyVario project. I have had a lot of success, but that is for the next post. In this post I will provide an update of what has changed over the past year. The bottom line is that the concept I first had some years ago, then started developing in earnest about 18 months ago, remains a worthwhile pursuit.

There has been a little movement in the availability and price of some of my chosen components. The RN42 Bluetooth module has come down in price a little, it is still the cheapest one available and now appears to be more widely used. Microchip has recently bought Roving Networks so I expect that their marketing might will make it even more available in a few months time. The Microchip PIC's are cheaper, as are the batteries and most of the passive components.

The MS5611, the key pressure sensor module I selected, has been used by a range of hobbyists. The Arduino microcopter folks have successfully integrated it. The module is now available in hobby quantities on at least a few specialist websites ( for example). You can also get the sensors on breakout boards on ebay occasionally. I got my hands on a few samples from a friend, and ordered got some breakout boards from ebay while I was away. Moreover, there is at least one commercial vario using the MS5611, the Flytepark microvario ( This is the culmination of Hari Nair's work and I once more congratulate him, not only for this vario, but his ongoing commitment to share his work with an open design.

I am not the only one looking at a bluetooth vario and over the past year others have got similar products to market and further discussed them on forums. The FlyNet vario is one example of something very similar to what I want to build ( It is more expensive than I am targeting (over $200) and it seems like the application and design are not open. However, the interface protocol is. I am considering using the same interface protocol as it is very similar to what I am currently using. For me to change will only take a few lines of code. I would add semi regular (once every few seconds) temperature updates, but I am less keen to allow users to change the device name.

Android, the target platform, has continued to get stronger and there are now a wider range of much more capable devices. Importantly, it is easy to pick up a cheap second hand 'old' android phone that should work really well as a front end for the vario. A few recent Android devices now have integrated pressure sensors, but I am unsure if it is possible right now to use these sensors as the basis of a sensitive vario. I think not from my initial research. The sensors are either not sensitive enough (like 30 cm RMS at best) and in many cases the operating system will not return measurements faster than a few Hz. I am aiming for 10cm RMS measurements at 50Hz. There is a discussion about this on pgforum.

Based on all of that I recommenced the hardware prototype development with the aim of integrating the MS5611...