Posted on Feb 5, 2014

Aquaponics systems need a good water quality, and one of the parameters is pH value, which needs to be within a certain range in order for the fish and plants to thrive. This is of course also true for fish-only aquariums, but since I have an aquaponics system set up already, this is what I`ll focus on. There are a few pictures of the system in th

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is blog post: Debian on NSLU2 With USB Hard Disk and Homeplug Network (I`m using a Debian NSLU2 but it should be possible to use an Unslung NSLU2 too). The small NSLU2 computer has a USB connector and with a DS9490R1-Wire to USB adapter it`s easy to collect data from a 1-Wire unit onto a hard disk. Then I just need a pH-to-1-Wire adapter, which is what I want to build and describe in the upcoming blog posts. A 1-Wire bus has a much longer reach than a USB bus and that is very convenient for many purposes. The pH probe that is supposed to be connected to the voltage amplifier only sends out 0. 059 V per pH unit and using a coax cable will keep out noise. Coax cable naturally terminates in a BNC connector. The voltage signal coming from the pH probe is both positive (pH < 7) and negative (pH > 7). Since the power supply for the circuit is from an ordinary 12 VDC mains adapter and the signal is going to an A/D converter, the ground reference for the voltage amplifier is raised to ensure positive voltages only for the converter, assuming that a normal one is only able to handle positive voltages. I can`t help checking the uptime when I log in. I`m still amazed by how little maintenance this small NSLU2 computer requires. This is usually the case with Linux servers, but on top of that is has low power consumption and small form factor I almost forget that it`s there. Generation of graphs happens automatically so before making...

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