Pico Trackers

Project Pico Trackers
Status	Abandoned
Contact	User:Bertrik_Sikken
Last Update	2019-07-14

Current status:

• software is basically ready
• pico tracker boards still have to be populated with actual electronic components

Intro

This page is about a so-called tracker for use with small ("pico") balloons, which is light-weight electronics board carried by a balloon and sends telemetry back to earth.

Software

The software of the payload tracker basically does the following:

• get position data from the GPS receiver
• get temperature and battery voltage (optionally barometric pressure)
• broadcast this data using a radio transmitter (RTTY, 70cm band, about 10 mW)
• repeat until battery is exhausted ...

The source code can be found at https://github.com/bertrik/picoballoon

It is based on the source of the pFalcon balloon by Nick Blommen.

To build it:

• install platformio
  • sudo apt-get install python-pip
  • sudo pip install platformio
• use platformio to compile it (libraries are downloaded automatically)
  • pio run

Special features:

• (runs the GPS in low-power mode for extra battery savings)
• resets the RFM22 radio every 8 cycles, in case it goes weird because of low temperature

Hardware

The hardware consists of a custom PCB, a uBlox6G GPS receiver, an RFM22B transmitter, all controlled by an ATMega328.

Power budget

To reduce the power consumption as much as possible, the board runs at a low voltage, 1.8V. The AVR clock frequency needs to be limited to 4 MHz, as this is the fastest the AVR can run at this voltage. See here for more information on running at low-voltage / low-frequency mode.

Current estimates:

Component	current	Remark
RFM22B	27 mA	27 mA @ +11 dBm transmit
uBlox 6G	12.2 mA	22 mW @ 1.8 V Power Save Mode (1 Hz)
AVR	1.7	active current, 4 MHz, 3V
Total	41 mA	current drawn from the 1.8V boosted voltage

Assuming 1.2V average battery voltage and adjusting for step-up ratio (1.8V / 1.2V) and voltage converter efficiency (60%), this means about 103 mA average current draw from the battery. An Energizer 1.5V primary lithium battery has a capacity of about 3000 mAh, so it is expected to last approximately 29 hours (3000 mAh / 103 mA).

Weight budget

Most commonly used for pico balloons seems to be the Qualatex 36 inch foil balloon, see [1]. This balloon weighs about 37g and has a volume of about 100 liter. See here for a graph of reachable height vs payload weight and maximum free lift to reduce the chance of bursting.

A possible alternative balloon is a Qualatex 36 inch latex balloon, weighs about 35 gram and a volume of about 400 liter (fully inflated).

Rough weight estimates:

Component	weight	Remark
Balloon	37 g	assuming Qualatex 36 inch latex
Battery	15 g	one 1.5V lithium AA (non-rechargable)
Enclosure	10 g	insulation to reduce RFM22B drift, "rope", etc.
PCB + components	5 g	rough guess
Miscellaneous	5 g	battery holder, wiring, antenna, etc.
Total	72 g	35 g excluding balloon

Schematic

Schematics:

• File:Picofalcon - Power.pdf
• File:Picofalcon - Top Level.pdf

Andere benodigde onderdelen

Designator	Description	Manufacturer	Manufacturer Part Number	Manufacturer series	Package	Value
ANT1	ANTENNA	Johanson Technology Inc	1575AT43A0040	GPS ANTENNA
C1	Capacitor - non polarized				0805	0.1uF
C2	Capacitor - non polarized				0805	0.1uF
C3	Capacitor - non polarized				0805	0.1uF
C4	Capacitor - non polarized				0805	0.1uF
C5	Capacitor - non polarized				0805	18pF
C6	Capacitor - non polarized				0805	18pF
C7	Capacitor - non polarized				0805	0.1uF
C8	Capacitor - non polarized				0805	0.1uF
C9	Capacitor - non polarized				1210	10uF
C10	Capacitor - non polarized				1210	10uF
C11	Capacitor - non polarized				0805	0.1uF
C12	Capacitor - non polarized				0805	1uF
CON2	6 pin 2.54mm Dual Row Pin Header
CON3	SMA	Emerson	142-0701-801	SMA (End-Launch)
CON4	CON JST BOX 2P	JST				JST 2P
CON5	3 pin 2.54mm Pin Header
FB1	Ferrite Bead 0805	Murata	BLM21BD102SN1D	EMIFIL		FB1
L1	SMD Shielded Tiny Power Inductor WE-TPC, L=2.5µH	Wurth	744031002	WE-TPC 3816		2.5 µH
LED1	Led				0603	2mA - 1.8V
LED2	Led				0603	2mA - 1.8V
R1	resistor				0805	2K2
R2	resistor				0805	2K2
R3	resistor				0805	10K
R4	resistor				0805	10K
R5	resistor				0805	1K6
R6	resistor				0805	1K6
R7	resistor				0805	10K
R8	resistor				0805	475K
R9	resistor				0805	182K
U1	GPS	UBlox	MAX-6G
U2	uC	Atmel	ATmega328P of [2]		ATMEGA328P-AU
U3	Tranceiver	HopeRF	RFM22B
U4	Pressure Sensor	Bosch	BMP085
U5	DC/DC Regulator	TI	TPS61200		tps61200drct
XTAL1	4Mhz Crystal	TXC CORPORATION	AT-4.000MAGE-T		HC49/US	4MHz

Parts Pricing

Upu's store

• Zo'n €33,- per setje (gps+antenne, 434MHz zender)

Farnell

• Om van alles één te hebben is het ongeveer 7,87 euro.