Talk:PH Meter
Question : in the large circuit schematic, there seems to be a contradiction. The configuration table for the 14V version shows R1/R5/R6 as 10/10/12k respectively. It states on the right-hand side that the schematic itself is for the 14V version, but the schematic shows the other values.
I assume the schematic is correct and the column headers in the table are swapped. Please confirm ?
- i believe you're right. The circuit seems to be for 14v output but the table's values are swaped.. u_u sry. Don't have the program installed atm to edit it, will need to do so later unless maybe can photoshop it.. eris
Question: Is the pin numbering wrong on the TL062 chip? there is a ping 11? should'nt that bee pin 8? And if you look in the datasheet http://www.datasheetcatalog.org/datasheet/stmicroelectronics/2294.pdf
The voltage is swapped. pin 8 is Vcc+ and pin 4 is Vcc-
2009/03/23 - The above mentioned images have been corrected, and a capacitor was added to improve stability in noisy environments. :D
- I cant seem to get this to work on 0-14 or 0-5v. The readings will not go low enough.
op-amp: http://www.datasheetcatalog.org/datasheet/stmicroelectronics/2294.pdf
hmm, will it read but just not entirely to 0? Have you adjusted vr2 ? You may try changing the values of one of the two resistors r5 or r6..
Cheap commercial meters
You can get a PH meter at the garden shop for $15 or so like the Rapitest that seem to use the dissimilar metals method. It clearly works (the needle moves) but I have no idea how accurate or reproducible it is. There's no way to calibrate it. You're just supposed to clean one of the probes with the included piece of scotch brite, take a little of your soil and mix it with distilled water into a nice mud, stick the probe in and take the reading from the needle.
Has anyone tested one of these to see of they are worth hacking? Janus303 15:06, 14 June 2011 (EDT)
the glass probe
I've found a little "glass probe" into an old pen-style pH meter. That consist into a glass bowl with inside a silver wire submerged of liquid, the wire is isolated to come outside the glass.
I was wondering if i can try to use this probe, or if the probe need 2 connections wire (to connect to the ground to probe like that seems to be in schematic diagram).
thx for sharing all that very usefull things ;).
