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USB Long-Term Weather Logger

Using I2C sensors for atmospheric pressure, temperature and humidity

USB Long-Term Weather Logger
This stand-alone data logger displays pressure, temperature and humidity readings generated by I2C bus sensors on an LCD panel, and can run for six to eight weeks on three AA batteries. The stored readings can be read out over USB and plotted on a PC using gnuplot. Digital sensor modules keep the hardware simple and no calibration is required.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Extra info / Update

- Accurate measurement of atmospheric pressure, temperature and humidity without calibration
- Store up to six records (each containing pressure, temperature and humidity readings) per hour
- Non-volatile storage for 8191 data records
- Up to eight weeks’ stand-alone operation from three AA cells
- Calibrated sensor modules with digital outputs for pressure, temperature and humidity
- Data can be read out over a USB interface



Issued: August 17, 2011.

The schematic as printed in the September 2011 edition needs complementing with two 3.3 kohm pull-up resistors, R6 and R7, as follows:


R6 between SDA (Pin 27/IC2) and VCC;

R7 between SCL (Pin 28/IC2) and VCC.


This correction does not affect the circuit boards supplied by Elektor, or the PCB artwork files that may be downloaded from this page.

A corrected schematic is included in the software download file for the project, # 100888-11.zip.


Issued: October 18, 2011.

In tbe parts list, the value of R5 should read 3.3 kOhm, not 1.3kOhm.

Download the BOM list
The BOM (Bill of Materials) is the technically exhaustive listing of parts and other hardware items used to produce the working and tested prototype of any Elektor Labs project. The BOM file contains deeper information than the Component List published for the same project in Elektor Magazine. If required the BOM gets updated directly by our lab engineers. As a reader, you can download the list here.
Want to learn more about our BOM list? Read the BOM list article for extra information.
Component list

R1 = 220kOhm
R2 = 33kOhm
R3 = 10MOhm
R4 = 10kOhm
R5,R6,R7 = 3.3kOhm

C1, C2 = 47pF
C3 = 10nF

C4,C5,C9,C10 = 100nF
C6 = 1µF MKT 5mm lead pitch
C7 = 470nF
D1,D2 = BAT42
T1 = BS170
IC1 = 24AA512
IC2 = ATMEGA88-20PU, programmed, Elektor # 100888-41
IC3 = LP2950-3.3 or -3.0
S1,S2,S3 = 6mm switch, PCB mount
S4 = single-pole switch
X1 = 32.768-kHz quartz crystal
LCD1 = DOGM162W-A (Electronic Assembly)
Mod1 = BOB-FT232R-V2.20 (Elektor # 110553-91)
Mod2 = humidity sensor HH10D (Hope RF, Elektor # 100888-71)
Mod3 = pressure sensor HP03S (Hope RF, Elektor # 100888-72)
K1 = 6-pin (2x3) pinheader (optional for ISP interface)
20-way socket strip SIL for LCD1
18-way (2x9) socket strip for MOD1
5-way socket strip for MOD2
IC socket for IC1 (8-way) and IC2 (28-way)
PCB, Elektor # 100888-1
Printed circuit board: order code 100888-1
Ready-programmed microcontroller: order code 100888-41
BOB-FT232R V2.20 serial-to-USB module: order code 110533-91
HH10D humidity sensor: order code 100888-71
HP03S atmospheric pressure sensor: order code 100888-72
Project software: file # 100888-11 (free download)

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