insideGadgets

A tiny temperature logger with minimal parts using the ATtiny13A/25 and a 512Kbit I2C EEPROM powered by a 3V CR1220 coin cell. Data logged can be extracted to a computer by using the A25TTL Reader module with a USB cable.

The A25TTL uses V-USB: http://www.obdev.at/vusb/

(Logger on the left and the Reader on the right. Please note that since I’ve hand cut the PCBs, they aren’t perfectly square and some may have the outside border silk screen still present.)

Features
– Compact design with temperature logging and USB transfer on separate PCBs. You can have multiple A25TTLs and only need a single A25TTL Reader.
– Low power consumption, at least 6 month battery life using 1 minute logging
– Measure temperature from -40C to 125C
– Uses an external 512Kbit I2C EEPROM which allows for 32,768 readings (2 byte values)
– Programmable logging delay time ranging from 1 second to 1 year in 1 second increments
– Easily transfer the logged data to your PC via USB using the A25TTL Reader which plugs into the A25TTL
Note: No information on time is recorded when logging.

Specifications
PCB Board: 17mm x 12mm (Logger), 31mm x 16mm (Reader)
Voltage: 1.8V to 5.5V
Current used when sleeping: 4uA
Current used when logging – thermistor on and write to EEPROM: 5mA (max), 3mA (average) for 28ms
Resolution of temperature (2 bytes): 0.16C (rounded up or down in 0.2C increments)
Accuracy of thermistor: within 1% -/+
Accuracy of timer: within 10% -/+
Operating temperature: -40C to 125C (Most CR1220 batteries only support -40C to 70C)

Download

The download file includes:
– Source code and compiled main.hex file
– Parts list, step by step guide and instructions on use (View it online here)
– PCB bottom ready for home etching
– PCB top ready for home etching (rotated horizontally)
– PCB Guide
– Schematic
– Example results
– Pictures of finished product

v2.0_Rev.2 (2 September 2015)
– Update A25TTL_Reader program to correct program delay bug

v2.0 Rev.1 (10 October 2014)
– Reduced code size to fit on an ATtiny13A
– Moved reader temperature conversion function to the a25ttl_transfer.exe program so now you can modify it easily without reprogramming the ATtiny

v1.1 Rev.1 (1 October 2014)
– Updated logger to work with any I2C EEPROM
– Updated reader temperature conversion function to use Beta parameters in order to use a new 1% thermistor
– Updated reader to allow for hot plugging in loggers

v1.0 (20 March 2013)
– Initial Release

Results

The graphs below show the results, you can also download the Excel files to see the raw data.

7 Loggers in room – Download

3 Loggers in freezer – Download

1 Logger under car hood – Download

Buy the Kit

To reduce shipping costs the kit is sent via the Airmail letter service for $3 and the usual delivery time is 7 – 12 working days (however it sometimes can take 20 working days depending on your location); we ship via Australia Post. Please note that since I’ve hand cut the PCBs, they aren’t perfectly square and some may have the outside border silk screen still present – this was done to reduce manufacturing costs.

A25TTL v2.0 Logger – pre-assembled – $11 [Discontinued as of 5 Jan 2016]
This item comes pre-assembled and ready for use. After adding this to the cart, remember to come back and add the A25TTL Reader to the cart too.

A25TTL v2.0 Logger – assembly required – $8 [Discontinued as of 5 Jan 2016]
This item requires assembly and soldering including soldering SMD parts – for this reason, this item is not recommended for beginners. After adding this to the cart, remember to come back and add the A25TTL Reader to the cart too.

A25TTL v2.0 Reader – $7 [Discontinued as of 5 Jan 2016]
This item requires assembly and soldering.

.

This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License.