Book Analog Interfacing to Embedded Microprocessors
• Noise that would be introduced on an analog signal sent down a long
cable may be eliminated by transmitting a logic-level frequency signal
instead.
• Measuring frequency instead of analog values may allow a simpler micro-
processor to be used, since an ADC is not required.
In many cases, you can convert an analog input, such as temperature, to a
time-based signal that can be measured with a microprocessor. An IC that can
do this is the Maxim MAX6576 (and a related part, the MAX6577). The
MAX6576 is a 6-pin surface-mount (SOT-23) device that converts tempera-
ture to a square-wave output. The period of the output signal is proportional
to temperature. The MAX6576 has two pins that are tied high or low to select
an output range of 10, 40, 160, or 640 ms per °K.
Using frequency in this way permits a microprocessor to measure temper-
ature with a single pin. The microprocessor software can perform this mea-
surement in several ways.
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