If you think that Humidity and Temperature Sensors are good business for you then I can help you learn and build this at very low investment. Invest and buy 100 Humidity Sensors (HS1101 wwww.sensorstechnology.com/industrial.html or www.humirel.com) for only US$500 and buy 100 NTC thermisters for another US$500 and then you can build 100 temperature and humidity transmitters with display for about US$25 each. This will be industril grade with market value of about US$100 (normally US$250) range. You can have 300% margin above investment. Considering other costs involved. 100% profit is very likely.
Investing 10000 US$ should be ideal to get another US$10000 as profit. If you can manufacture and sell 3000 such instruments per year then your benefit will be about US$30000 per year. If you wish to take an advantage then try out the idea. Complete design is available as technology transfer under agreement and sensors under special discount price for small industry manufacturer support program.

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Prof. (Dr.) Shyam, Managing Director for Sensors Technology Private Limited. Gwalior, MP474001, India.