HAB balloon projects
OM3BC tracker info
Extended information about the OM3BC tracker: www.om3bc.com/docs/payload/payload_en
My aim with the Eagle files is to make a tracker that is as simple to build, cheap and light as possible. A fully assembled board should weigh about 1–1.3 grams, and a fully assembled board with solar cells and antenna about 3.5 grams.
I'm using 6 of the smallest available (19x39 mm) solar cells in series to power the board. It runs from and to a solar angle of 15–19°, depending on the GPS used.
After more than 25 launches over the years and probably more than 10 PCB revisions I have come to this final(?) design. The intention of this page is to ease building and configuring the OM3BC APRS / RTTY / CW tracker.
The rar file at the bottom of this section contains all files mentioned in this small write-up.
Firmware and parts
There are two firmware versions, depending on which GPS module you intend to use:
fw7.5 is for u-blox Max modules. I have so far only tested the Max7q and Max7c, both working well. The low-voltage "c" version gets a bit longer runtime because of its lower voltage demands. Max6 and Max8 should work just as well.
fw14 is for the ATGM336 GPS, a "new" cheap module that can be found for around $3 on AliExpress. No flight mode needs to be set on this module, and it has been tested to over 32000 m at the time of this write-up.
The rar also holds Eagle PCB files for two PIC footprints. I have tested both the L and LF versions of the PIC and could not see any advantage in the low-voltage (LF) version. All versions of the Si4x6x I have tried have worked well: so far SI4060, 4463 and 4063.
Fuse settings
The most important setting for reliable startup of the board is to enable the Watchdog Timer (WDT). Set everything to 1 as in the picture below. To do this, press "Configuration:" in the PICkit3 software before you program the board.
You can read about the fuses in pic18f26k22.pdf (in the rar).
Schematic
Settings I'm using
MYC SA6BSS-9 DEVIATION 425 POUT 8 (pout 100 using 4060; pout 8 = 25 mW on a 4x63) APRS on HOLD 2 TAIL on 2 INTEMP yes REF 19199985 UBLOX on (= atgm336) TTEXT RTTY 434.5/100b7n2 Temp:\W Gps:\B UNPROTO APRS V wide0-0 (= do not use digipeaters; leave unchanged if you want to use them) RFRQ 434500000 (puts the RTTY up in the ISM band)
I'm using the Termite terminal to set up the board. It is in the rar, as is the PICkit3 software. Termite also supports macros, so you don't have to enter every setting each time you set up a new board.
Programmer
To configure the board you have to use an RS232 programmer. The only type that has worked reliably so far is the one in the picture. Look for it on eBay or AliExpress; it should cost around $3–5. Note the DC jack, electrolytic caps and LEDs. The output voltage is 5 V. To reduce it, put 2 diodes in series on VCC, or preferably use a 3.3 V LDO.
PicoTracker
Help and hints to get the PicoTracker from hamshop.cz going.
What you need
A USBasp AVR programmer, which costs a couple of dollars on eBay. You will also need a 10-pin to 6-pin adapter.
Software: Arduino IDE 1.0.5-r2, plus some libraries and settings for the Arduino IDE: Arduino files.
Setting up the Arduino IDE
Place boards.txt and programmers.txt in the \arduino-1.0.5-r2\hardware\arduino folder, and place the folders rfm22 and TinyGPS in the \arduino-1.0.5-r2\libraries folder. Don't forget to restart the Arduino IDE so the changes take effect.
Open the Arduino IDE and go to Tools – Board. At the bottom you will see "Tracker Low Power (1.8V, 4 MHz) w/ ATmega328". Then open Tools – Programmer and select USBasp.
To avoid breaking the GPS chip with too high a voltage, I recommend desoldering the VCC pin on the 10-to-6 pin header, or putting a pin-header jumper there, and powering the tracker board from its own power source. This only applies to the MAX6, as the MAX7 and MAX8 GPS can handle 1.65–3.6 V.
Burning the bootloader and uploading
Burn the bootloader via Tools – Burn Bootloader. It is set with fuses that let the board run on an external crystal at low power; you can see the fuses in boards.txt. Read more about fuses at Fuses 1 and Fuses 2.
That's about it. Load the picotracker.ino code from GitHub (ok1cdj/Picotracker), set the frequency and baud rate in the code and choose File – Upload using programmer.
If all goes well it will start compiling and transfer the code to the tracker board. Never mind if it says something about COM1; the USBasp doesn't use COM ports. Make sure you put the 6-pin programming header on the right way round.
There is a lot of code besides OK1CDJ's that is compatible with this board; see the bottom section of this page.
Notes
Note 1: The tracker does not start if it can't talk to the GPS. A tip: fit all components except the GPS module and load CHEAPO, which works without the GPS module.
Note 2: There may be an error in the original 3.1 schematic for the 1.5 V – 1.8 V converter. It states R6 = 820 kΩ and R8 = 430 kΩ, but the correct values are the other way round: R6 = 430 kΩ and R8 = 820 kΩ. This is now corrected on GitHub. I also got R6 = 220 kΩ and R8 = 430 kΩ to work.
Finally, a big thanks to Ondrej, OK1CDJ, for making this available and maintaining and updating the GitHub files, and to all the other great HAB sources on GitHub.
My own home-brew tracker
This is my own 
project, using readily available modules from eBay, much like these projects: Tracker 1, Tracker 2, Tracker 3.
Update: I made one tracker this way but it died, probably from static electricity, and it was a pain to build. I abandoned the idea when I found a PCB maker that makes the boards for $1 a piece, which is much easier.
The PCB version
Some modifications to the original design made it about 5 grams lighter. First I got the PCB made at 0.8 mm thickness. I also removed the front part where the GPS chip antenna used to be, and made the GPS antenna pad a little bigger so I could solder on a 1/4-wave GPS antenna about 45 mm long.
The PCB maker I used is Dirty PCBs. It takes about 3 weeks for the PCBs to arrive. I got 14 PCBs for $14 including postage, but the board has to be under 5 cm long, so you have to modify it as I did.
