Measure humidity and temperature on one TTL line

Posted on Jun 6, 2012

By combining the responses of an Analog Devices ( AD590 temperature sensor and a Humirel ( HS1101 humidity sensor, you can generate a single TTL-level signal containing information from both sensors (Figure 1). This design uses a 74HC123 monostable multivibrator, IC1, to form a free-running oscillator. The AD590 current source (1 µA/K), IC2, and a fixed 1-nF capacitor, C1, control the timing of the first monostable multivibrator in the 74HC123.

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