Srinivasan M (Neutrino) is so fond of DIY electronics. His latest build is a cool one. A “smack to wake” digital contact thermometer with an OLED display and runs on a single coin cell. You turn on the device by giving it a gentle smack against your palm, reminiscent of how you would shake a Mercury thermometer. This is accomplished by integrating a Piezo-electric sensor. The temperature sensor used is a metal capsulated DS18B20 with 1-wire interface. The device has to run on a single CR2032 cell. This means every component must draw the least possible current from the battery. For this reason, Srinivasan carefully selected the components and optimized the configuration and code to use minimum current. The end result was an operating time of around 140 days on a coin cell. Impressive!
The microcontroller used in the project is the ATTiny85 in an SMD package. Interestingly, this tiny controller had everything to implement this project, including an I2C interface and analog input pin. Arduino IDE was used to develop and flash the firmware on the MCU. The entire circuit consumes an average of 3mA when working at 1MHz clock and only 58uA during deep sleep. The device enters into sleep mode after it is active for while.
Everything was nicely arranged on a piece of perfboard. Srinivasan designed a 3D printable enclosure for this. I especially like the design of it. Very clever indeed. Have a look at a few pictures of the completed build. He has also released a complete video tutorial giving a walkthrough the build process.
All of the design files and source code used to build this project are available for you to freely download. See his previous interesting builds by visiting his YouTube channel and the links below.
[All images were provided by Srinivasan]
- Instructables Tutorial – https://www.instructables.com/Contact-Digital-Thermometer-With-Deep-Sleep-Attiny/
- Hackster.io Tutorial – https://www.hackster.io/Neutrino-1/contact-digital-thermometer-with-deep-sleep-attiny85-8c93f8
- Github – https://github.com/Neutrino-1/digital_thermometer
- YouTube Video – https://youtu.be/o19y9fz3n2o
- Srinivasan’s Instagram – https://www.instagram.com/srinivasan2020/