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rupez1 avatar image

How do I use the digital inputs in cerbo GX

Community, I’ve installed a Cerbo GX. I think I’m happy with the relay functionality. 3v3 octocouple relay to allow power to a 12v fan. The digital inputs are a whole other issue and are doing my head in.
I’ve read the manual and some background stuff but I think I’m not getting it.

1. Are the inputs powered at 3v3? Do I just need to complete a circuit to change the input state, I.e. short across the digital inputs (I don’t think this is the case but I need to check)?

2. So what I‘d like is a digital signal when the bilge pump goes on. Here’s what I think I need to do… Put a relay across the pump power. Have that provide a 3v3 signal to the cerbo digital input. I’m aware that I need a diode or octocouple to protect the cerbo from inductive current/voltage due to the relay coil. The problem is I can’t find such a circuit anywhere.

3. Because I can’t find anything it makes me think I’m way off with my plan. Can you guys suggest a better way of getting an on/off output from the bilge pump?

Thanks in advance,

cerbo gxVenus GX - VGXsensor
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6 Answers
pwfarnell avatar image
pwfarnell answered ·

The inputs are powered and if you have a volt free switch connected between the digital input it will change state when the switch closes, shorting across the digital input. I have a couple of simple float switches connected like this in my bilges to indicate the bilge pumps are not emptying the bilge water.

You may be able to do other things by forcing a voltage on the input ( within limits) but i do not know the details.

I would also like to know when my bilge pump works but i have not solved that because my bilge pumps do not have float switches but inbuilt conductivity probes and I have no easy point to take a voltage signal from.

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jeffryk avatar image
jeffryk answered ·
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This was exactly what I was looking fo. Thanks very much, total legend.

randyb128 avatar image
randyb128 answered ·

To answer your exact questions:

1. From the Cerbo GX manual, the inputs are pulled up with a 10k resistor to 3v3 (3.3 volts). Yes, you can just complete a circuit to ground (common) and the input should trigger.

2. If you provide a dry (zero potential) N.O. (normally open) relay contact then you can just run a wire from common through the contact and back to one of the digital inputs of the Cerbo GX.

3. The method jeffryk is suggesting above is the correct way to do this. The solution is inexpensive and no relay is required. The optical isolator provides a noise free input for the processor. Running low voltage processor input wires more than very short distances is never a good idea. The isolator should be as close as feasible to the Cerbo GX. If you need any help wiring up the optoisolator, post on here and I should be able help you out. I did the same for both my bilge pump and a high level water proximity detector.

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Randy, This is vexing me a little. I’ve the noise free switch/ optical transistor/ optocoupler. (See below). I measure 3.2V across the cerbo inputs. I’ve connected 12V across the switch (to simulate a pump running) but I don’t know which of the three transistor terminals to use!!! VCC, OUT, or GND to connect to the cerbo. I’ve also tried just shorting the wire’s from the cerbo but no alarm. What am I missing?

18a6f79a-f89c-415d-9fa4-37f4611e7522.jpeg

jeffryk avatar image
jeffryk answered ·

I will see if I can find a pic from my test setup, I just left the boat a couple of hours ago and will be likely back in the morning. I have it working by the 12 volts connected to the side with 2 connections in your picture. the other side has the wires going to the cerbo connected to the ground and positive to the "out" port. When 12v is applied the red light on the optocoupler should light up. I did have to switch the digital setup in the cerbo to be inversed in the cerbo device setup.

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Thanks pal. I’ve the red led lit but haven’t reversed any cerbo settings although I’d still have expected it to work but in a reverse sense?

jeffryk avatar image
jeffryk answered ·

alarm-setup.png (16.4 KiB)
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jeffryk avatar image
jeffryk answered ·

Rupez1. In there Cerbo, do you have digital input that you are connected to in the Cerbo enabled located at Settings - I/I - Digital Inputs? Does the device show up on your devices pages and show connected? I sent you the setup page last night.

I have attached a pic of my test setup. I put in a simple toggle switch to simulate turning on and off the pump, but it should not matter, once 12v is connected to the other side the Cerbo should see the circuit as "open". My test setup for the wires going to the Cerbo use some extra wire with ferrule connectors that I had from other VE stuff I have bought. As long as the device shows connected in the cerbo then you know you have good connections in the proper ports. See pic attached and I hope this helps. Bilge pump test.jpg


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