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I would need some directions on how to build a simple circuit with a temperature sensor.

OBJECTIVE: The device measures the time between two temperature values. The values are read from a sensor on the circuit every minute. The device starts measuring the time interval at 10C (or lower) and stops measuring at 20C (or higher). If the temperature has not reached 20C in 5min the LED starts blinking. When the LED starts/stops blinking a notification is sent over bluetooth4 to a remote device (if any).

NOTES: The device should use a coin battery which should last for >=1 year (as little processing as possible).

QUESTIONS: - Doable? - What components are you proposing?

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  • \$\begingroup\$ Doable if the LED is low power SMD and this case happens VERY rarely. The chip proposed by @HL-SDK should be able to get your battery lasting that long if you are smart with the sleep modes. Also, you should find a temperature sensor that can be configured to wake up the chip at defined temperature readings. \$\endgroup\$ – chwi Feb 24 '14 at 8:58
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I propose you use a nordic nRF51822 chip that includes the temperature information in advertisement data with an advertisement period of 1 to 2 seconds. Use connectable undirected advertisements. If something wishes to connect to the temperature monitor, implement an appropriate temperature characteristic.

Bluetooth SIG Temperature measurement characteristic

Do not include a LED, this will ruin your battery life. Is the LED REALLY needed? Do all the data processing on the host side.

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  • \$\begingroup\$ Thanks for the proposal. Unfortunately the LED is required and the processing should be done localy. Any other ideas? \$\endgroup\$ – xpepermint Nov 12 '13 at 8:11
  • \$\begingroup\$ Why, and why? FWIW you'll probably get 100 feet out of bluetooth low energy. \$\endgroup\$ – HL-SDK Nov 12 '13 at 16:10

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