741 Based Light Sensor:  CdS photocell used for light/dark controlled relay

Circuitry for inexpensive Relative Humidity Measurement: National Semiconductor Application Notes,04-Nov-1995

Dual Comparators Stabilize Proximity Detector: 02/16/98 EDN-Design Ideas

Infrared Body heat Detector:

Low cost relative humidity transmitter uses single logic IC: 11/08/2001 EDN - Design Ideas /  The low-cost percentage-relative-humidity radio transmitter in Figure 1 operates in a cold-storage warehouse for vegetable storage at temperatures of 1 to 5 C. It is generally difficult to collect such data from a low-temperature area with high humidity and low illumination. The transmitter design is simple: It uses a readily available, capacitor-type percentage-relative-humidity se... .

Measure humidity and temperature on one TTL line: 08/30/2001 EDN - Design Ideas / By combining the responses of an Analog Devices (www.analog.com) AD590 temperature sensor and a Humirel (www.humirel.com) 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. .

Remote humidity sensor needs no battery: 04/04/2002  EDN - Design Ideas / Using ac-line power sources and batteries for remote humidity sensors is undesirable because these sources can be troublesome if you mount them in inaccessible points, such as smokestacks, cold-storage chambers, or darkrooms, where maintenance is difficult and inconvenient. Figure 1 shows a simple way to remove the power source from the humidity-sensor circuit. .

Signal Conditioning Precisely indicates Humidity: 02/02/98 EDN-Design Ideas

Simple Circuit Uses Optical Fiber To Send RelativeHumidity Data : 04/01/02 Electronic Design - Ideas for Design / The circuit shown in the figure measures relative humidity in air at the low temperatures found in applications like cold storage of food items and greenhouses. Instead of using electrical signal cables that...  

Tiny Dew Sensor:

Transmitter senses triple relative humidity figures: 09/26/2002  EDN - Design Ideas / The circuit in Figure 1 is a triple, relative-humidity sensor and radio transmitter. Sensors 1 and 2 form two gated oscillators with natural frequencies of 10 and 5 kHz, respectively, at relative humidity of 50%. The gated oscillators use variable resistances R2 and R3, respectively. Together, these two oscillators generate FSK-modulated outputs at output of IC1B, Pin 6..