Asynchronous and Pulse Inputs
Two headers (J7 and J8) are provided for
asynchronous inputs. Voltage to J7 is selectable at 5V or
3.3V using jumper JP2. J8 is fixed at 3.3V. We usually use
J7 for a GPS antenna module such as the Byonics
GPS5HAOEM.
If 5V is selected, be sure to use a 3.9K resistor for
R19 to limit current to the Propeller input pin. If 3.3V is
selected, a resistor is not needed and you can use a wire
jumper instead of a resistor at R19.
Either of these inputs can be used for many other
devices. On several flights, we used J8 to provide power
to and count pulses from the “MightyOhm” Geiger
counter (see Resources sidebar).
It has also hosted a prototype gamma ray scintillator
designed and built at UNH. J7 could be configured as an
output in the code, and used to drive an LCD.
Flight Enable Tab
The flight enable tab at JP1 is a jumper that is pulled
shortly before launch. It essentially means “committed to
launching.” Pulling the tab starts the main program loop
and initializes the mission clock. We attach a long piece
of brightly colored tape to the jumper which adds
visibility, grip, and more importantly some drama.
Relay Outputs
The relay outputs are both unpowered, and simply
provide a switch closure that can be used to trigger
various external devices such as cameras. Or, they could
be wired into a pull-up on another microcontroller such
as might be used for an independent student science
experiment.
BCD Input
For several years, we have been thinking about a way
to transmit commands up to the microcontroller from the
ground during flight. Suggested by our colleague, Lou
Broad at Timberlane Regional High School, a dual tone
multi-frequency (DTMF) signal can be generated by a
handheld radio on the ground and transmitted to the
balloon payload over a suitable amateur radio frequency.
June 2017 33
QTY NAME ORDER SCHEMATIC SYMBOL
2 0.1 μF ceramic capacitor, 0805 Mouser 81-GRM40X104K25L C1, C4
2 0.1 μF ceramic capacitor, through-hole Jameco 544921 C2, C3
1 Hirose DM3D Parallax 452-10017 Conn1
4 1N4001 diode, through-hole Jameco 35975 D1, D2, D3, D4
7 Two-pin header, Molex KK Jameco 232266 JP1, J5, J6, J11, J12, J13, J18
4 Three-pin header, Molex KK Jameco 232274 J7, J8, J9, J10
1 Four-pin header, Molex KK Jameco 232282 J14
2 Five-pin header, Molex KK Jameco 232291 J19, J20
2 30-pin header (cut to needed lengths) Jameco 103342 J1a, J3a, J2a, J4a, JP2, JP3
4 Green LED, rectangular through-hole Mouser 604-WP113GDT LED1
1 Red LED, rectangular through-hole Mouser 604-WP113HDT LED2, LED3, LED4, LED5
1 2N2222A transistor Jameco 38236 Q1
1 TIP120 power transistor Jameco 179291 Q2
1 10 KΩ, SIP- 6 bussed network Jameco 268032 RN1
4 100 Ω, 0805 Mouser 667-ERJ-6GEYJ101V R8, R10, R11, R13
1 180 Ω, 0805 Mouser 667-ERJ-6GEYJ181V R1
3 220 Ω, 0805 Mouser 677-ERJ-6GEYJ221V R21, R22, R23
1 10 KΩ, 0805 Mouser 667-ERJ-6GEYJ103V R2
3 220 Ω, through-hole Jameco 690700 R12, R6, R19
1 3. 9 KΩ, through-hole Jameco 691008 Alternate for R19
1 470 Ω, through-hole Jameco 690785 R9
1 1.1 KΩ, through-hole Jameco 690873 R18
1 3. 3 KΩ, through-hole Jameco 690988 R15
2 4. 7 KΩ, through-hole Jameco 691024 R17, R3
5 10 KΩ, through-hole Jameco 691104 R4, R5, R7, R14, R20
1 100 KΩ, through-hole Jameco 691340 R16
1 Relay, SPDT RadioShack 275-0005 RLY3
2 Relay PB1167-ND RLY1, RLY2
1 Piezo buzzer RadioShack 273-074 SPK1
2 Two-cond terminal block Pololu 2420 TB3, TB4
2 Two-cond terminal block Jameco 2094485 TB1, TB2
1 4N25 optoisolator, DIP- 6 Jameco 40985 U2
1 LM4040 voltage reference, 2.5V, SOT23 Mouser 926-LM4040CIM325NOPB U3
1 MCP3204 ADC, DIP- 14 Mouser 579-MCP3204-CI/P U1
PARTS
LIST