APPROACHING THE FINAL FRONTIER
■ BY L. PAUL VERHAGE
BALLOONSATS, PONGSATS, AND
THE IDAHO CLUSTER
THIS MONTH, I HAVE SEVERAL TOPICS to discuss.
The nice thing about them all is that they can be
expanded upon. So, expect to hear more about them
in the coming months.
■ FIGURE 1. Hobo Datalogger Controller.
I’ve used three forms of data loggers in near space. The first two use
the MAX186 and ADC0834 and are
components in the flight computers
I’ve designed. The third data logger
I’ve used is a Hobo (see Table 1).
When considered for their typical
application, each data logger is very
capable. For instance, the Hobo is outstanding for student BalloonSats. But it
does have a limited voltage range
(only 2. 5 volts). There are many sensors that require five volts to operate
and they produce an output voltage
that can span five volts.
How do you interface
a five volt sensor to a
2. 5 volt Hobo? The
easy answer is to
power the sensor with
a five volt voltage regu-
lator and send its output through a
voltage divider. Figure 2 shows the
Hobo datalogger converter I’ve
designed to do just this (see Table 2).
Since I like to use the Hobo with
four external channels, I designed the
converter to be used with four sensors.
The sensors plug into the input port of
the converter and are powered with a
low drop-out regulator, the LM2940T-
5. I selected this regulator because it
can operate with as little as 5. 3 volts.
The output voltage of each sensor is
divided in half with a high precision
voltage divider circuit. The sensor voltages are input to the Hobo with 3/32”
stereo jacks. The
Hobo uses stereo
jacks because it
power for the
into it. The tip is
the input voltage
Voltage Bits of Voltage
Range Resolution Resolution
4.096 12 1.0 mV
5.0 8 19. 6 mV
2. 5 8 9. 8 mV
■ TABLE 1
■ FIGURE 2
LM2940T- 5 low drop-out voltage regulator
High precision resistors (1K or larger)
22 µF electrolytic capacitor
Three pin receptacles
3/32 inch ( 2. 5 mm) stereo jacks
■ TABLE 2