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app-dat/home-plant-dat/ph-tester-dat/ph-tester-dat.md
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@@ -8,6 +8,7 @@
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![](2026-01-25-18-25-51.png)
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+![](2026-01-25-18-46-21.png)
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- [[display-dat]] and [[mcu-dat]] == [[stm8-dat]]
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@@ -15,8 +16,18 @@
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- [[OP-amp-dat]]
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+the control board
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+
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![](2026-01-25-18-26-02.png)
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+![](2026-01-25-18-46-06.png)
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+
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+![](2026-01-25-18-46-38.png)
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+
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+the sense board
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+
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+![](2026-01-25-18-45-50.png)
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+
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[[OP-amp-dat]] for [[ph-tester-dat]]
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@@ -26,13 +37,13 @@ You need an **electrometer-grade or FET-input op-amp**.
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### Suitable op-amps for pH measurement
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-| Op-amp | Input bias current |
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-| ------------- | --------------------- |
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-| [[LMP7721-dat]] | 3 fA |
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-| [[LMC6001-dat]] | 25 fA |
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+| Op-amp | Input bias current |
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+| ----------------------------- | --------------------- |
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+| [[LMP7721-dat]] | 3 fA |
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+| [[LMC6001-dat]] | 25 fA |
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| [[TL072-dat]] / [[TL082-dat]] | ~65 pA *(borderline)* |
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-| [[OPA129-dat]] | 75 fA |
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-| [[AD8605-dat]] | 1 pA |
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+| [[OPA129-dat]] | 75 fA |
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+| [[AD8605-dat]] | 1 pA |
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> **Rule of thumb:**
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> Input bias current should be **< 1/1000 of electrode current**
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@@ -66,3 +77,5 @@ Typical pH front-end architecture
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- Ibias >50 pA → no
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+## ref
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+