Hardware Reference
In-Depth Information
This program can be tested on the Dragon12-Plus demo board by rotating the poten-
tiometer. The circuit shown in Figure 12.18 contains a signal-conditioning circuit which
consists of two Op-Amps (741), five resistors, and three different power supplies (25 V,
212 V, and 12 V). This circuit allows the user to utilize the whole dynamic range of the
HCS12 ADC. However, adding a signal-conditioning circuit adds cost to the resultant
product. It should be used sparingly. By setting the
V
RH
input to 1.8 V, the designer can
eliminate the use of the signal conditioning circuit shown in Figure 12.18. After changing
the circuit, the designer will need to change the formula for translating the ADC result
back to the temperature reading. This change is straightforward and hence is left as an
exercise problem.
The IH-3605 is a humidity sensor made by Honeywell. It provides a linear output from 0.8
to 3.9 V in the full range of 0 to 100 percent
relative humidity
(RH) when powered by a 5-V
power supply. It can operate in a range of 0 to 100 percent RH, 240
o
to 185
o
F. The pins of the
IH-3605 are shown in Figure 12.19. The specifications are listed in Table 12.10. The IH-3605 is
light sensitive and should be shielded from bright light for best results.
Specification
Description
Total accuracy
Interchangeability
Operating temperature
Storage temperature
Linearity
Repeatability
Humidity stability
Temp. effect on 0% RH voltage
Temp. effect on 100% RH voltage
Output voltage
±2% RH, 0%-100% TH @ 25°C
±5% RH up to 60% RH, ±8% RH at 90% RH
-40° to 85°C (-40° to 185°F)
-51° to 110°C (-60° to 223°F)
±0.5% RH typical
±0.5% RH
±1% RH typical at 50% RH in 5 years
±0.007% RH/°C (negligible)
-0.22% RH/°C
V
OUT
= (
V
S
)(0.16 to 0.78) nominal relative to
supply voltage for 0%-100% RH; i.e., 1-4.9 V
for 6.3-V supply; 0.8-3.9 V for 5-V supply; sink
capability 50 A; drive capability 5 A typical; low-
pass 1 kHz filter required. Turn on time < 0.1 s
to full output.
4 to 9 V, regulated or use output/supply ratio;
calibrated at 5 V
200 A typical @ 5 V, increased to 2 mA at 9 V
IH-3605
VS supply requirement
GND
V
OUT
V
S
Current requirement
Figure 12.19
■
Honeywell
IH-3605 humidity sensor
Table 12.10
■
Specifications of IH-3605
The IH-3605 can resist contaminant vapors, such as organic solvents, chlorine, and
ammonia. It is unaffected by water condensate as well. Because of this capability, the
IH-3605 has been used in refrigeration, drying, instrumentation, meteorology and many
other applications.
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