Sunday 26 May 2013

Hardware prototype version 6 ready

After a few months of messing about with the hardware design I have settled on the final design for prototype version 6. There are a few new features, the look is more polished, and the usability has been improved.

The image above shows the final assembled prototype (on the right). I plan to ship the prototypes in a package that includes the circuit board in heat shrink (as shown on the left) and the case in component form. For version six the final assembly will be left to you. This saves me time, the postage cost is less to many destinations, and it will fill in five minutes on a quiet evening. This video shows the process for final assembly and testing.

Upgrades from earlier versions

There are a lot of little tweaks. Here are the highlights:
  • Integrated Hardware Audio. I spoke about this in an earlier blog post. I pretty much did what I said in that post. When I started the BlueFlyVario journey I was initially resistant to do anything on the device except send pressure data to a phone. However, after tinkering with the hardware audio I realised it was a feature that everyone had to have. Integrated audio makes the vario much more versatile, for the addition of only about $3 of additional components. At some point I might write a blog post that describes all of the audio settings that you can adjust on the hardware via the connected app. 
  • Heatshrink. The effect of a small piece of 43mm clear PVC heatshink makes the device feel much more robust. The heatshrink protects the components and helps hold the battery in place. The device is about 11mm thick in the heatshrink. I suspect that some users will just leave the BlueFlyVario like this, and will not bother putting it in the perspex prototype case. Especially if they are going to put it under the padding in their helmet. The PCB mounting holes can be used as tie down points. 
  • Pressure Sensor cover. The pressure sensor is really sensitive to sunlight. This meant that users of earlier versions had to hide the device away in flightdecks and pockets. A small piece of 3mm neoprene allows air pressure through but blocks sunlight completely. This is very effective and even dampens wind noise a little. I left the white cover on the neoprene to make it easier to put the heat shrink over it. Beware that pressing on the neoprene does affect the pressure so you should mount the device in a spot where it is not going to be pushed in and out often. 
  • New PCB layout. The PCB layout needed to be pushed around to incorporate the audio circuitry. Also all LED's, resistors and capacitors were changed to 0603 size, and some values were altered to optimise the design. The circuit schematic and PCB layout below shows the new design. Despite R8 being listed as a 10 ohm resistor, I am actually using a 0 ohm resistor in the final design. It makes the audio louder and does not increase current consumption much. 

So now I am planning to start churning these out at cost for collaborative hardware developers. I have made a small batch and have the parts for the next batch on order. I have put the plans for prototype version 6a (the experimenters version) on hold until I see what the initial interest is like.