Simple and cheap temperature logger: v2.1 [UPDATE: EEPROM in BOM corrected (SST25WF080) ]

Hi everyone!

It’s been too long since the last update. But it’s there! The last version of the temperature logger, the hardware and the source code.



The changes since the last version:


  • New footprint for the PIC18F26J50, easier to solder.
  • Only 0603 or bigger resistors/capacitors.
  • The serial EEPROM is now a SST25WF080, still 8Mb, but easier to source.
  • Some components price-optimized (USB connector, switch, 3.3V reg).


  • Each logger can get a number, shown in the mass storage device drive name: simply add an asterisk (*) followed by the number you want to assign to the logger (between 0 and 65535) in the config.txt file (after the logging period), save the file and format the logger.
  • Bug fixes in the FAT12 functions, but the logging space is still limited to the half of the EEPROM.
  • Other bug fixes (month and year change, added robustness). The memory and the EEPROM are now scanned when you plug the logger back, to get the last data and reconstruct the filesystem in the case of a battery failure.

Temperature Logger 2.1: Schematics and basic BOM

The Altium files

The source code (based on Microchip Applications libraries -Device – Mass Storage – SD Card data logger- MPLABX)

I also made a program/debug adapter (especially useful for debugging):


USB-Temperature-Logger-Programming-tool1This is the “office” version of my previous peg-adapter 😉

A lot of people were asking me if I was selling these loggers. Unfortunately, no. The design and functionalities are sexy, but I don’t have the capacity to launch a production on my own. And if I had do make only a small batch, the price would be totally uncompetitive.

A big thanks for all the people who donated a little something to motivate me!! (or to help me be more ashamed of the lack of updates)

All the contents (except the parts of Microchip’s code in the source) are under the Creative commons license, Attribution – Share Alike – Non Commercial.

Creative Commons License
Simple temperature logger: v2.1 by Jean Wlodarski is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

Simple and cheap temperature logger: New update coming

I’m working on a new revision of the temperature logger: new PCB and new firmware. It’s easier to solder, as the resistors/caps are now 0603 instead of 0402 and the PIC package is now a SSOP28 (instead of QFN).
The sleep current is smaller than 10uA and below 1mA when measuring the temperature (plus a few mA every 20-or-so logs, when writing to EEPROM).

The EEPROM is a SST25WF080 (still 1,8V 8Mb), as the previous Atmel memory is not available any more.

Some 3D renderings of the PCB:

Simple and cheap temperature logger 2.1

The USB connector is a Multicomp MC32604, cheaper than the previous MCKUSBX-SMT2AP1S-W30. (I couldn’t find a suitable 3D model for the PCB rendering)

The ISCP connector for programming the firmware  is SMT but fits the Microchip’s ICD header:

The new firmware has functions for the new EEPROM, a low battery indication, more robust logging and USB update capabilities. Plus a lot of bugfixes and optimizations.

Now, to complete the firmware, I have to build at least one logger, which means ordering the PCB and the components. That’s why I added a “donate” button to this blog (on the top right side of the page, just under the title), especially I don’t earn any money with this blog and content is free (and will stay free, of course).

If my work helped you, if you find it interesting, if you want more articles and more projects, dropping a few coins will motivate me and help me to materialize all the projects waiting in my head. 🙂

Stay tuned for more!