Data Logger with Serial Interface

Posted on Feb 7, 2014

The data logger consists of a simple op-amp amplifier circuit that amplifies the signal and sends it to be digitized by a PIC16F688 microcontroller, serialized, and sent to the computer`s serial port via a MAX232 serial driver: I guess you are already wondering about some of the unusual arrangmenents in the analog part in the schematic diagram abo

Data Logger with Serial Interface
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ve. Part of it is because of the voltage differences between the analog and digital part: the op-amps work on 12V while the microcontroller and the serial driver require 5V. Part of it is to make the different kind of sensors I plan to use easier to connect. Finally, this is partly because I`m really lazy and when I got the things to work to my satisfaction I refused to change anything. The point is - unusual or not, it works. IN1 is a DC-input with a range of 1-11V. Whatever voltage is applied to IN1 is directly passed to the amplifier. Try to keep the voltage centered around the 6V point for best results. IN2 is an AC (self-centering) input with a range of ±5V. The trimmer potentiometer R1 connected to this input centers the signal at 6V when the sensor signal is not changing. Switching between inputs is done by shorting the JP1 jumper. You can either use a switch there and do this manually, or wire JP1 into the connectors you use to plug-in your sensors (which is the way I did it). Before finishing with the input part, notice the optional amplifier OP2 in the lower part of the diagram. Some sensors based on a voltage divider work best when the voltage is split close to the half point - in other words, if you have a resistor/photoresistor bridge and in the particular conditions the photoresistor has 10k resistance, the signal will be stronger if the other resistor in the bridge is also around 10k. Use the trimmer...

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