MAXREFDES300

The MAXREFDES300 needs only a simple setup to start logging the temperature.

Hardware Requirements

Package contents:

• MAXREFDES300 board
• MAX32625PICO board
• 10-pin ribbon cable
• Micro USB cable

Other requirements:

• Either A76/LR44 battery or external power supply (required, but not included)
• EPC Gen2 UHF/RAIN protocol-based reader (optional, if host machine is available)
• Host machine with COM terminal program (optional, if RAIN reader is available)

Recommended RAIN reader:

Figure 2 shows the CS108 reader by Convergence Systems Limited, which is the recommended reader to wirelessly read the data from the MAXREFDES300# board. It is available for purchase on the Axzon website.

Logging the Temperature

Insert the button cell battery, then press the PWR button on the board once to turn on the board and begin logging. It is loaded with firmware that measures and logs temperature every one minute for one hour. The alarm thresholds are set to +5°C and +20°C.

Press and hold the PWR button for 10 seconds to turn off the board.

Reading the Data

The data in Table 1 can be read from the RFM405 using an EPC Gen2 UHF/RAIN protocol-based reader. Each address contains a 16-bit value.

Modifying the Default Parameters

1. Power on the MAX32625PICO board by connecting the Micro USB cable to a host machine.
2. On the host machine, start a COM terminal program like PuTTY or Minicom at 115200 baud.
3. Connect the 10-pin ribbon cable between the MAXDAP adapter on the MAXREFDES300# and the MAX32625PICO board.
4. Power on the MAXREFDES300# board by inserting a A76/LR44 button cell battery or by applying an external power supply on the EXT+ and EXT- pins at 1.5VDC.
5. Once the datalogging has started, type any key on the COM terminal to enable an interactive terminal.

The following actions are available for the user:

• Change Log Interval – Modify the rate at which temperature is measured and logged.
• Change Log Duration – Modify the length of time for which datalogging should run.
• Change Alarm High Threshold – Modify the upper temperature threshold.
• Change Alarm Low Threshold – Modify the lower temperature threshold.
• Show Current Configuration – Display the current values of parameters.
• Start Logging – Begin datalogging.
• Print All Logs – Print all logs since power was applied to the board, if not already deleted by the user.
• Print Log Brief – Print maximum temperature, high temperature violations count, and low temperature violations count for all available logs since power was applied to the board, if not already deleted by the user.

Things to Remember:

• Start Logging must be selected by the user to apply the changes.
• When Start Logging is selected, the user may choose to delete previously recorded logs.


1. When prompted, enter ‘y’ or ‘Y’ to delete all previous logs or enter ‘n’ or ‘N’ to keep previous logs.
2. If ‘n’ or ‘N’ is selected, a log entry with Time = 0 and Temperature = 0 is created to differentiate between changing parameters.


• When the interactive terminal is enabled and no user interaction occurs for 60 seconds, the system will return to logging mode and all recent user changes will be discarded.
• If power is disconnected from and reconnected to the board, all of the user’s changes will be lost and default values will be restored.

The MAXREFDES300 reference design showcases the capabilities of the MAX32660 microcontroller in low-power mode to log the temperature measured by the Xerxes RFM405 passive sensor.

The MAX32660 is an ultra-low power Arm® Cortex® M4 with FPU-based microcontroller with the biggest memory in its class. It supports wearable-grade power technologies and is designed especially for IoT applications where power, performance, size, and cost are all equally important.

The RFM405 is a wireless temperature sensor IC. Smart Passive Sensing™ technology enables battery-free and maintenance-free sensing. An antenna accompanies the sensor for complete operation, and a RAIN/UHF reader can be used to read it.

The MAX20310 is a compact PMIC that manages the power on the board. It is a SIMO design where a single inductor can provide two programmable voltage rails, making it an ideal choice for space-constrained, battery-powered applications.

MAXREFDES300 operates on one button cell (LR44) battery and has a power button to turn on or off the board. A folded dipole antenna allows UHF communication with the RFM405 sensor.

A 10-pin, Arm Cortex debug connector on the board can be used to connect to a host machine through a MAX32625PICO board with a similar connector. The MAX32625PICO board is a tiny development platform that can be used as a debug adapter or as a target platform.

Block Diagram