The block diagram above illustrates a data logger backup system using the MAX32625PICO and three  DS28EC20's, which are 2.5kB 1-wire EEPROMs.

The data logger of interest is DS1922L, which is a temperature logger with 8kB Data-Log Memory. The DS1922L is a rugged stand-alone temperature logger capable of storing temperature data for long periods of time (years!), making it suitable to be deployed in the fields. However, once the battery internally is depleted, all the data stored previously would be lost. The backup system powered by a single coin cell battery ensures that measurements logged by the iButton remain intact even if the battery of the iButton dies.

1. MAX32625 has a hardware 1-wire master that can be used to communicate with any 1-wire slave devices except EPROMs since the PICO is not equipped with a 12V programming pulse circuitry. 1-wire is useful as it only requires one wire for power and communication, and another for ground. Each 1-wire device is equipped with unique 64-bit ROM IDs so unlike I2C, multiple 1-wire slaves with the same part number can be placed on the same bus without needing to worry about address collision.

2. Three DS28EC20s, which can store 2.5kB each, are required to back up 8kB data.

3. The PICO board will fetch temperature measurements from the iButton periodically, and save them to the EEPROM. Firmware will need to be implemented. The OneWire library is available on mbed and will be used as the API to communicate with the data logger and the memories. https://os.mbed.com/teams/Maxim-Integrated/code/OneWire/

Note: Even though iButton was the data logger of interest, the data backup system can extend to any other sensors and data loggers with compatible interfaces to the PICO board (SPI, I2C, 1-wire). More 1-wire EEPROMs can be added on the 1-wire bus if more memory is required. Alternatively, there are also flash memories with SPI interface available.

For more information on 1-wire, please refer to https://www.maximintegrated.com/en/app-notes/index.mvp/id/1796

Datasheets can be found below:

MAX32625PICO: https://datasheets.maximintegrated.com/en/ds/MAX32625PICO.pdf

DS1922L: https://www.maximintegrated.com/en/products/digital/data-loggers/DS1922L.html

DS28EC20: https://datasheets.maximintegrated.com/en/ds/DS28EC20.pdf

MAX40200: https://datasheets.maximintegrated.com/en/ds/MAX40200.pdf