Near Space Helium Balloon

S11D336B

Hey Guys,
I'm developing a near space helium balloon (weather balloon) in my spare time (with some friends of mine). I wanted to share my experience with the Propeller community (as I will be using the Parallax Propeller to implement the Telemetry/Recovery systems).

Other projects which have done something similar:
http://natrium42.com/halo/flight2/
http://www.w6xe.net/~jmeehan/balloon/

rules, etc:
http://www.eoss.org/pubs/faqloon.htm

1. Telemetry
Obviously to find this thing once it comes back down, I'm going to need some way to track / locate it. After doing some research and looking at various xBee devices, I'm starting to lean toward leveraging SMS messages on a cell phone network. There are obvious advantages/disadvantages to this. Firstly, modern cell networks are ALMOST everywhere. Meaning just about no matter where I land (crash land), I'll be able to receive position reports over SMS. I've already been able to send SMS messages from my computer using my personal cell phone. AT Command Set reference was quite useful.http://www.smssolutions.net/tutorials/gsm/sendsmsat/

2. Recovery
I've seen some projects that use a parachute that kind of auto deploys when the balloon pops. I don't like this kind of system as the payload is significantly slowed during the whole course of it's descent which can allow the payload to drift many many miles. Because of this, I'd like to design a system which will deploy a parachute when the payload is descending and has reached an altitude of < 2000ft.

Here are some parts I have picked out so far for this development.

Propeller Backpack (because of it's small size)
http://www.parallax.com/Store/Microcontrollers/PropellerDevelopmentBoards/tabid/514/CategoryID/73/List/0/SortField/0/Level/a/ProductID/602/Default.aspx

Altimeter Module (for pressure and temperature)
http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/pressure/List/0/SortField/4/ProductID/780/Default.aspx

For the Telemetry system using SMS I'm looking at several pay as you go type cell phones. I liked this one the best so far because of the price.
http://www.walmart.com/ip/AT-T-GoPhone-Prepaid-Samsung-A107-Cell-Phone-Silver/15421486

At&t looks like the way to go for doing this because they offer unlimited everything for $2 per day of use. Meaning I only pay when I use SMS and I get that whole day for $2.

I haven't figured out how I am going to connect the Cell phone to the micro controller. I did find this cable.
http://bestcelldist.com/samsung_sgh_a107_serial_data_cable.html
But after a search on RS232 I found that RS232 can actually have a negative voltage. I don't believe the propeller can handle negative voltages on it's pins.
http://en.wikipedia.org/wiki/RS-232#Voltage_levels

In any case, I'm open to any comments or suggestions you guys have especially on connecting the cell phone to the Propeller.


Non-functional objectives (what we want to achieve):
1. Record high altitude video
2. Log atmospheric parameters at various altitudes
3. Expand our knowledge and experience in building autonomous and robotic systems


Functional objectives (what it does)
1. Records video using a camera (go Pro)
2. Reports it's GPS coordinates over SMS (using a cell phone and GPS)
3. Can cut away from the helium balloon (either with a timeout or by SMS command)
4. Can automatically deploy a recovery parachute
5. Records atmospheric and location parameters
6. Logs mission and flight time
7. Regulates the internal temperature of the payload
8. Emits loud buzzing noise for easier recovery
9. Payload should be modular and assembled with connectors for easy maintenance.

S11D336B

Connecting the cell phone to the Propeller:

I was looking at this IC
http://search.digikey.com/us/en/products/MAX232CPE%2B/MAX232CPE%2B-ND/947834
Which could convert RS232 to TTL for the microcontroller.

Which could connect to this cable:
http://bestcelldist.com/samsung_sgh_a107_serial_data_cable.html

However, when reading the product description it says that the RS232 cable converts the phones TTL to RS232. So, if I could find a pinout for the cell phone, I could probably just hook the propeller directly to the cell phone's serial port instead of going from TTL to RS232 back to TTL.

Any thoughts?

Thanks,
George

Circuitsoft

You probably can, but there's no way to know where in the cable they put the TTL/232 chip. So, for now, get the cable, cut it in half, plug it into your PC and see what the signal levels are.

S11D336B

Not sure what happened, but it looks like my first post disappeared. Anyway to get that back?

S11D336B

Not sure why, but the first post keeps getting removed when I edit it. . . .Perhaps it has to go back for moderator approval?

S11D336B

Looks like its back. At this point I'm posting just to get my post count up . More info tomorrow.

Moderator Monkey

S11D336B wrote: »

Not sure why, but the first post keeps getting removed when I edit it. . . .Perhaps it has to go back for moderator approval?

Salutations,
That is precisely what is happening. For reasons unknown to me your posts kept getting trapped in the spam-filter. I asked one of the other monkies to look into the issue and they assured me that this shouldn't be a problem anymore. Sorry for any inconvenience or confusion this may have caused.

S11D336B

Makes sense, but if I can avoid buying a $40 cable, I'd like to. Are there any sites that anyone knows of that would have the pinout of that phone? a Google search didn't reveal much.

For that matter, any cheap phone anyone knows of that has a pinout.

Circuitsoft wrote: »

You probably can, but there's no way to know where in the cable they put the TTL/232 chip. So, for now, get the cable, cut it in half, plug it into your PC and see what the signal levels are.

S11D336B

No problem. Thanks for taking care of it so quickly. You guys are like lightening.

Moderator Monkey wrote: »

Salutations,
That is precisely what is happening. For reasons unknown to me your posts kept getting trapped in the spam-filter. I asked one of the other monkies to look into the issue and they assured me that this shouldn't be a problem anymore. Sorry for any inconvenience or confusion this may have caused.

Tubular

The prop can handle a negative voltage if you use a big enough series resistor, to limit the current to 500uA (as per the datasheet).

For -12v this equates to 24k. Often the RS232 negative voltage is more like -5~-6 volts. The resistor may cause problems with really fast baudrates, as it introduces an RC filter, but you'll probably be fine. You just need to try it.

The serial objects have an 'invert RX' option which might be required.

S11D336B

That is a good idea. I'll try that. I did go ahead and purchase the RS232 cable. I also was able to pickup that phone (Samsung A107) at Walmart. I tried first to hack the charging plug. I was able to get the plastic case off, but only the + and - charging pins were populated on the connector. Also, the connector on the PCB (phone side) has too tight of a pitch for me to realistically hand solder a wire to it. If I had the pinout I might try it, but with the cable on the way I'll just wait. I'll post pictures later.

Tubular wrote: »

The prop can handle a negative voltage if you use a big enough series resistor, to limit the current to 500uA (as per the datasheet).

For -12v this equates to 24k. Often the RS232 negative voltage is more like -5~-6 volts. The resistor may cause problems with really fast baudrates, as it introduces an RC filter, but you'll probably be fine. You just need to try it.

The serial objects have an 'invert RX' option which might be required.

prof_braino

Have you looked at the Prop Android Bridge from MK Borri?

http://forums.parallax.com/showthread.php?130380-Android-Debug-Bridge-on-a-prop

If I understand correctly, it allows terminal type access to the Android device. The Android can provide terminal, storage, processing, and communications services, and the prop can provide interface to the sensors and actuators.

I recently received my first android device, so I should be looking into the android bridge soon. If you pursue this option, maybe we can collaborate.

S11D336B

I had not seen this yet. Thanks for bringing it to my attention. It looks like a very useful library. The original plan (before I posted) was to use a spare Droid I had sitting around the office. However, I found that I couldn't get a carrier to activate this phone without also signing up for a $30+ per month data plan (+ 9.95 for another line + 5 for text package). I didn't want to spend $45 a month just to get telemetry running so I ended up going with the Samsung a107 (which I can get unlimited use out of for $2 a day on the days I use it).

If you know of a way to get an a android phone up and running on the cheap, I'd love to hear about it.

thanks,
George

prof_braino wrote: »

Have you looked at the Prop Android Bridge from MK Borri?

http://forums.parallax.com/showthread.php?130380-Android-Debug-Bridge-on-a-prop

If I understand correctly, it allows terminal type access to the Android device. The Android can provide terminal, storage, processing, and communications services, and the prop can provide interface to the sensors and actuators.

I recently received my first android device, so I should be looking into the android bridge soon. If you pursue this option, maybe we can collaborate.

prof_braino

Once I get the phone talking to the prop, I will work on connecting to WiFi in the lab, then I will mess with getting the phone to work. I think there might be a way to swap in a SIM card from another phone and just get the phone part working. It might not send real time video streams, but it might be able to phone home.

S11D336B

Cool. Let me know how it goes. My Droid is CDMA. . . So, I can't do any trickery with the sim card.

prof_braino wrote: »

Once I get the phone talking to the prop, I will work on connecting to WiFi in the lab, then I will mess with getting the phone to work. I think there might be a way to swap in a SIM card from another phone and just get the phone part working. It might not send real time video streams, but it might be able to phone home.

eiplanner

@ S11D336B

Not sure if this option is too pricey for the project but I was just browsing through posts last night for fun and ran across someone who put up this link and it looks like a very interesting device to maybe have in ones toolbox just for fun:

https://store.diydrones.com/DroneCell_p/br-dronecell-01.htm

I also saw a page for sim cards (can't remember the link now) that was thru T-mobile that had a text only plan (no data) for like $4.99/mo for 30 or fewer SMS's up to $9.99/mo for a couple hundred SMS's.

I don't know anything about making it work with the Prop; I just figured I'd post because it seems like something that could fit into your project.

S11D336B

Looks like a nice option. I'll save it in case the GoPhone I have doesn't work out.

I also updated the first post with some requirements we determined.

eiplanner wrote: »

@ S11D336B

Not sure if this option is too pricey for the project but I was just browsing through posts last night for fun and ran across someone who put up this link and it looks like a very interesting device to maybe have in ones toolbox just for fun:

https://store.diydrones.com/DroneCell_p/br-dronecell-01.htm

I also saw a page for sim cards (can't remember the link now) that was thru T-mobile that had a text only plan (no data) for like $4.99/mo for 30 or fewer SMS's up to $9.99/mo for a couple hundred SMS's.

I don't know anything about making it work with the Prop; I just figured I'd post because it seems like something that could fit into your project.

Dave Hein

Have you considered using an APRS transmitter instead of a cell phone? APRS will provide telemetry throughout the entire flight. A cell phone will just provide telemetry at the beginning and end of the flight. Which GPS module are you using? You should use one that works above 50,000 feet.

For recovery, I suggest using a parachute that will open when the payload begins to descend. The descent from 100,000 feet will take about a half hour or less. Even with the chute open the payload will fall at a rate of several hundred MPH at high altitudes because of the thin air. It will slow down as the air gets denser closer to the ground.

Make sure you use a battery that will last for the duration of the flight. You don't want the battery to die before the payload lands, or it will be difficult to find it. The battery should last for 3 or 4 hours to give you enough margin.

S11D336B

I looked into APRS a a little bit. I understand that a cell phone probably won't work (optimistically) above 3000' because of the directional nature of cell phone towers. I had considered supplementing the cell phone reporting system with some other transmitter (like APRS/Packet Radio). The only concern I have with such a solution is that I haven't found one that was affordable and versatile.

I want to eventually be able to not only have the payload report it's position, but be able to send commands (like cutdown the payload, etc).

To achieve maximum versatility, I was looking for some solution like this

Payload: 2m radio - modem - micro controller.

Ground Station: 2m radio - modem - laptop

Meaning that each would be a discrete component I could interface with.

I still have a bit of research do to in understanding packet radio, but I was hoping to start with something like this
http://www.gigaparts.com/store.php?action=profile&sku=ZAL-DJ-175T
and interface the micro controller with it.

If any of your guys have links to tutorials about setting up packet radio / APRS I would appreciate them.

Thanks,
George

Dave Hein wrote: »

Have you considered using an APRS transmitter instead of a cell phone? APRS will provide telemetry throughout the entire flight. A cell phone will just provide telemetry at the beginning and end of the flight. Which GPS module are you using? You should use one that works above 50,000 feet.

For recovery, I suggest using a parachute that will open when the payload begins to descend. The descent from 100,000 feet will take about a half hour or less. Even with the chute open the payload will fall at a rate of several hundred MPH at high altitudes because of the thin air. It will slow down as the air gets denser closer to the ground.

Make sure you use a battery that will last for the duration of the flight. You don't want the battery to die before the payload lands, or it will be difficult to find it. The battery should last for 3 or 4 hours to give you enough margin.