pH sensor measurements unstable

[MisterF]

Hi,

So I've been working on a project for my fishtank. In the fishtank there is a temperature sensor and a pH sensor. These are connected to an arduino Uno WiFi board along with an RTC module, SSR and a nextion display. The following is connected to the SSR: lights, heater, pump (all for the fishtank).

When I'm measuring the pH in the calibration liquid, or any other liquid at all, I'm receiving stable readings. When I put the pH sensor in the fish tank and turn anything on (lights, heater or pump), the measurements starts to go up and down and isn't stable anymore. In the circuit there is also a 100 uF and 100 pF capacitor. Am I missing something or is there a way to prevent this from happening?

[DrDiettrich]

@MisterF

Am I missing something

Do you use analog or digital sensors?

If analog, what's your ADC reference voltage? It should be very stable, not depending on Vcc noise and fluctuations.

[Grumpy_Mike]

@MisterF

In the circuit there is also a 100 uF and 100 pF

That 100pF is going to do nothing it should be a 100nF ceramic capacitor, sometimes called a 0.1uF capacitor.
The long leads on the capacitor make them very much less affective. They should be placed on each module.

It is interference from your mains operated devices that is causing the problem. This is down to u tidy wiring and lack of noise suppression on these devices especially the motor,

[MisterF]

First of all, thanks for the response. Sorry, but I'm rather new with noise filtering etc.

@DrDiettrich

Do you use analog or digital sensors?

If analog, what's your ADC reference voltage? It should be very stable, not depending on Vcc noise and fluctuations.

The temperature sensor is digital, the pH sensor is analogue. The ADC reference voltage is 4.95V if I'm not mistaken.

@Grumpy_Mike

That 100pF is going to do nothing it should be a 100nF ceramic capacitor, sometimes called a 0.1uF capacitor.
The long leads on the capacitor make them very much less affective. They should be placed on each module.

It is interference from your mains operated devices that is causing the problem. This is down to u tidy wiring and lack of noise suppression on these devices especially the motor,

So if I'm reading correct, I should place multiple 100 nF ceramic capacitors? Should I place them between the VCC and GND or should I place them over the data line from sensor to the arduino? If I remember correctly, the ceramic capacitors should be placed closely to the arduino?

[DrDiettrich]

@MisterF

The temperature sensor is digital, the pH sensor is analogue. The ADC reference voltage is 4.95V if I'm not mistaken.

This means that the reference is Vcc, with all noise on that line. Use at least one of the more stable built-in references.

[Grumpy_Mike]

@MisterF

Should I place them between the VCC and GND

Yes.

@MisterF

should I place them over the data line from sensor to the arduino?

Only if you want to destroy the fast changes in a signal.

@MisterF

I remember correctly, the ceramic capacitors should be placed closely to the arduino?

Close to the components, that means sensors and other boards.

Electronics is a bit like using LEGO, when the build gets big you have to do extra things to make it stand up.

[MisterF]

In the new draft I changed the 100 pF with 0.1uF and added a couple to all the boards connected. Is this what you are suggesting?

[Grumpy_Mike]

@MisterF

Is this what you are suggesting?

Yes sort of. The use of solderless bread board does open up all sorts of problems as there are long sections of wires going nowhere, just picking up interference.