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Simple 12-bit ADC datalogger with PC printer port interface

for research, teaching and hobby: temperature logging, electrocardiography, pletismography, light intensity monitoring, battery charging.
Suitable where signals with a DC component must be measured - a problem that can't be solved using a PC's sound card.

The design is similar to PICOTECH and uses a 12-bit analog to digital converter chip from a chip family made by MAXIM .
Thanks to the company MAXIM for donating free samples of their chips to everyone upon request!!! That allows to make an ADC for tight buget projects.


Single-channel dataloggers
The circuit is assembled inside a printer connector casing. This is a simplified version of data logger made by company PICO. It uses MAX1285 with 3.3 V power and 2.5 V internal reference. Input resistor divider increases the input range to the interval 0...+20 V (range suitable for car mechanics).  Power for the device 3.3 V is obtained from the LPT data lines and no external power is necessary.

2 up to 8 channels
More than one channel allows to record x-y plots and observe one signal influence on another. External power needed (for mobile applications can use USB or 5V available at the keyboard connector). Input range 0...5 V or -10...+10 V (based on MAX1270, MAX186).

The data acquisition program contains simple Qbasic code. Sampling rate is up to 100 Hz and could be increased to about 15 kHz using a compiled program.Time is recorded along with the data in a spreadsheet file. The Qbasic program does not work with Win XP that does not allow direct access to ports and it is apparently time to change to Delphi, Matlab, etc programming environments.

Here is a zip file with documentation for those who have more time than money. Similar ADC kit costs about 60 USD from and fully functional modules can be bought for about 200 USD from Swedish electronics re-saler ELFA . Another option for logging slowly varying signals is to use a digital pocket-size multimeter with RS232 interface.

Best wishes from Riga, Latvia!
a l n i s @ l a t n e t . l v