I work in a Chemistry Lab and have zero background in electronics/electrical engineering. My aim is to better control and document the calibration of tests so, I wish to design a system in which user inputs a value to the system and the provided value of fluids flows out of the pipe. For the purpose; I imagine I would have to use a solenoid fluid control valve, a raspberry pi keyboard module with a display and a flowmeter to save the total fluid fed to the outlet in a file on the SD Card.

To this extent, I have a working setup to calculate total fluid outlet using the flowmeter and a separate setup to control a solenoid switch. But I do not know how to relate it. Because the level in the tank and thus pressure can't be pre-decided, I cannot just open the solenoid valve for an x amount of time to dose water to the system. I realize that I would have to control the valve somehow with the flowmeter where the flow sensor cuts off the solenoid at the value of user's input.

I want to know how many Raspberry PIs I need for the job. Since my sensor and solenoid valve both require a 5V pin and pi only has 1, I am confused and also, I want to know if I can control the solenoid valve with values from the flowmeter using the pi computer.

  • On the basis of no apparent research you have decided Pi is the solution to your problem?
    – Milliways
    Feb 16, 2022 at 22:56
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    I did my research when trying to get a modbus device output to display to a screen. I used Raspberry Pi for it. Then I bought a small flow sensor and used Raspberry pi to get its output. Then I bought a solenoid switch and used raspberry pi to control it. Since it could do things individually, I assumed it'd be the right tool for the job Feb 17, 2022 at 3:18
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    If you had a Pi you must realise it has 2 5V pins (not that this is relevant). See Tour to see how this site works. and How do I ask a good question?
    – Milliways
    Feb 17, 2022 at 5:07
  • It is good that you have this experience, but I feel your question needs more focus. It reads as if you want someone to detail a complete design for you - that was my first impression. Your comment revealed that was not necessarily the case, but my suggestion is this: Break your problem down into smaller pieces, and consider making each "piece" a separate question. For example, concentrate on the flowmeter first: Show your setup & wiring, give your component P/Ns, run a test, show your results, describe the issues & ask a specific question about that. Rinse & repeat as they say.
    – Seamus
    Feb 17, 2022 at 7:13
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    Welcome -- but I think the question here is really about how to deal with calculating or otherwise dealing with the variable liquid pressure in the tank, with regard to which the Pi is tangential. That question is more appropriate to our larger site, Electrical Engineering.
    – goldilocks
    Feb 17, 2022 at 16:08

1 Answer 1


The Raspberry pi is more than adequate to do what you want. I will take a SWAG on the rest: For the 5V input it was addressed many times on this forum, this link should give you the information you want. The sensor output is more then likely a switch contact. GPIO to detect if external 5v source is turned on or off? For the solonoid you can use a relay module. They are readily available and not very expensive.

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