Book Analog Interfacing to Embedded Microprocessors
between 4v and 20v, and produce a voltage output that directly corresponds
to voltage. The LM35 produces a voltage of 500 mv at 50°C, with an additional
10 mv for every additional °C increase. The LM34 is calibrated for Fahrenheit
temperatures, and the LM35 for Centigrade. The outputs of the LM34/LM35
can be connected directly to an ADC or to a comparator.
Figure 3.5
LM335.
58 Analog Interfacing to Embedded Microprocessors
The National LM74 measures temperatures between -55°C and +150°C
and communicates with a microprocessor via the serial SPI/Microwire inter-
face. The LM74 output is a 13-bit signed value. The part contains a tempera-
ture sensor and a sigma-delta converter. It is available in either 3.3v or 5v
versions and comes in an 8-pin SMT package.
The National LM75 is similar to the LM74, but uses the I2C interface. The
LM75 has a narrower operating temperature range: -55°C to +125°C. The
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