Next stop: 18x13x6mm. 35nA (0.000035mA) sleep current.

A project log for micropower micrologger [mPmL]

A set-and-forget I2C/digital datalogger. Size: 25.3x 18x 10mm incl. battery. Runtime: > 1year

JanJan 02/25/2019 at 18:120 Comments

The micropower micrologger project is not dead. Quite the contrary is true. I've been testing this even smaller logger for a while now, in a basic (not fully assembled) variant:

It is working well. Power source is a CR1225 (on the back of the PCB). The timing is not done with an RTC but an TPL5110 nanopower timer. The next version will be even smaller, as I found a smaller battery holder from Linx Technology. The reset button will be removed as well.

The board uses 35nA in shutdown mode. The TPL5110 is activated at a set intervall and powers up the whole board. The Atmega does its job and sends an signal to turn off to the TPL5110 chip, when done.

Timing is only accurate to a few seconds (details see the datasheet!) due to being set by a resistor. But for this type of logger, the exact time is not critical.

The EEPROM will be a 2Mbit one, the sensor is the really small TMP112. Just recently @Edward Mallon posted a guide to use an onboard crystal/oscillator to measure temperatures. For this small logger this looks like an cool approach to save some money on the sensor (around 90 cents). But it needs per-logger adjustments, so I am not sure yet...