7 posts • joined 14 Dec 2011
The watch batteries don't have the capacity to power all the electronics. The GPS pulls about 25ma under acquire dropping to about 5ma once it gets into power saving mode. The only battery we recommend people use for this are the Energizer Ultimate Lithium's which are 1200mAH for the AAA and 3000mAH for the AA's and are known to work below -40'C. The watch battery is 24mAH so you can see the issue :)
For the record the tracker uses about 40-45mAH which is low, there are some inefficiencies in the step up convertor. The hardware in theory can squeeze more out of the battery as I can switch the GPS off entirely from the microcontroller but I've not coded this yet.
For this flight the 7.6g AAA will be fine gives over 26 hours. For the record nothing touches the L91 and L92 Energizer Lithiums for the weight vs capacity.
Re: Mechanism for emergency mission abort?
The loss of the payload last time was due to some dodgy weather data, we have a plan to verify the data prior to the launch this time (a smaller balloon going up a hour or so before).
Autonomous flight termination is possible and yes we have code to geofence an area and take appropriate action should we leave that area.
Due to the radio laws in the UK remote termination of the flight is possible but quite complex and a bit hit and miss, I doubt we have the time to implement this. You can use a Rockblock to do this but we lost the one they gave us :/
Yes there will be a live feed and yes I will remember to take my 3G SIM this time.
Re: 70cm Links
We use the license exempt 70cms band to transmit RTTY at 10mW. You don't need a license to do this and it is permitted for airborne usage. The APRS was transmitted on 144.800Mhz but to comply with the legislation in the UK the transmitter wasn't enabled until it left UK airspace. There are other European countries where its not permitted so the code had geofences in to disable the APRS to comply with the local laws.
Additionally the code prefixed my call sign with the correct ITU prefix i.e DL/M0UPU. The law is a little silly in this respect as the transmissions were received by UK stations and igated whilst the payload was over the Netherlands/ Germany.
Re: Warning on Iridium...
We've not had any issues with the Iridium in testing but for safely the GPS antennas is as far from the Iridium one as possible.
Re: Vias in Pads
You're entirely correct however I think the scanner just picked up the marks where the solder had been deposited, making it look like vias in all the pads. Just to confirm there are no vias in pads on the board at all.
It burst earlier this morning and splashed down in the Med shortly before 09:50. Good effort to all involved and especially the APRS operators in the Azores without whom we'd have probably lost it.