It's about one year ago that I ordered the DHT11 low cost humidity and temperature sensor. Now I found some time to make something useful with it: A USB stick sensor node.
When plugged in, it provides a serial interface which outputs the data in a readable format once a second.
This project utilizes only an DHT11 1-wire sensor and the programmer ez430U, which comes with every ez430-Kit from Texas Instruments. The ez430U has a MSP430F1612 micro-controller on it accompanied with a TUSB3410 chip for serial to USB conversion.
To re-program the F1612 you need a grown-up (4-wire capable) JTAG tool and a connection to the RESET and JTAG pins of the device. For our all convenience TI prepared already the test points TP2 (reset) and TP4-7 (JTAG) for that and you only need to solder a 5-pin header to it.
The DHT11 uses a proprietary 1-wire protocol with a pulse width coding. I developed a full timer and interrupt based code to request and decode the sensor data from the DHT11 while the main controller is powered down. As the sensor should only be read-out once a second, the MSP430 sleeps also during this period.
I've uploaded the complete project with some extra functions to read and write the EEPROM for the USB controller to GitHub.
Have fun building your own.
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