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Topic: Question regarding load switching (Read 297 times) previous topic - next topic

Klagemauer

Hello again, I just have a question regarding load switching.
I am trying to use a micro usb interface with different sensors.
some of the sensors need a +-3.3V output some need +-5V.
As I am using a differential signal, I am low on pins and
I do not have enough space to change the connector.

My question is if there is a method of switching the power rails
digitally, which does not create much distortion in the supply ?
Preferably in form of an IC.

Thank you in advance for your replies.

Klagemauer

I found the TPS22968 which is a dual load input switch which has a very low resistance when turned on.
I think I will try this.

wvmarle

Why not connect everything to the same power pins?
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

FredScuttle

Do you mean the sensors need different power AND logic voltages? Can you post a wiring diagram?
Awww! Who needs an instruction manual to use a simple chain sa......

Klagemauer

Thank you for your replies. I think I might have used the term "Load switching"
incorrectly. Please correct me if I did. What I meant was that I have multiple types of analog sensors
and I would like to use them on my data logger while being able to swap them.
However, some of them require +-3.3v and the others require +-5V. Initially I thought
about just connecting all of them to the interface and then wire up the respective power line on the
sensor's side but unfortunately I have not enough pins.


Why not connect everything to the same power pins?
I am unsure what you mean. With the digital switch I am tying to connect two power lines into one (one for +ve and one for -ve). So that I can switch between +5V & +3.3V on one while switching between -5V & -3.3V on the other.


 
Do you mean the sensors need different power AND logic voltages? Can you post a wiring diagram?
Yes, but unfortunately I do not have a the diagram available right now. So here please find attached a crude drawing of the idea.


wvmarle

I see two mistakes here.

First of all: there's no -3.3 and -5V available from the Arduino. Only +5V and +3.3V. I don't think I've ever encountered a sensor that needs a negative voltage anyway, so I'd be interested to know what special sensors you have that require a dual voltage supply.

Secondly: you don't run out of power pins, as there's nothing stopping you from connecting many devices to the same pin, provided that the total current they draw is what the Arduino can handle (which is not much, and also depends on how the Arduino itself is powered).
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Klagemauer

I see two mistakes here.

First of all: there's no -3.3 and -5V available from the Arduino. Only +5V and +3.3V. I don't think I've ever encountered a sensor that needs a negative voltage anyway, so I'd be interested to know what special sensors you have that require a dual voltage supply.
I am using an external power supply to allow me to reduce the noise.

Secondly: you don't run out of power pins, as there's nothing stopping you from connecting many devices to the same pin, provided that the total current they draw is what the Arduino can handle (which is not much, and also depends on how the Arduino itself is powered).
I am using an USB interface to connect the sensor to the ADC and since micro USB has only 5 pins I am limited to 2 power outputs 1 ground and 2 differential signal sources.

wvmarle

I am using an external power supply to allow me to reduce the noise.
And that's a dual power source? What do you use the negative side for?

Quote
I am using an USB interface to connect the sensor to the ADC and since micro USB has only 5 pins I am limited to 2 power outputs 1 ground and 2 differential signal sources.
This totally doesn't make sense. USB is a specific protocol, and it's definitely not analog.

Why don't you draw a complete schematic of what it is you're trying to do, plus a list of which sensors (with part numbers) you want to connect and how. There's less and less sense to this whole thing.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Klagemauer

This totally doesn't make sense. USB is a specific protocol, and it's definitely not analog.
I am just using the connector, not an actual USB protocol.



Why don't you draw a complete schematic of what it is you're trying to do, plus a list of which sensors (with part numbers) you want to connect and how. There's less and less sense to this whole thing.
Unfortunately I am currently not at home so I can't post it.

Wawa

#9
Jul 13, 2018, 05:40 am Last Edit: Jul 13, 2018, 05:42 am by Wawa
Seems OP is trying to design a shield for an stm32f103c8t6 with a MCP3903 A/D.
One of the cross-posts here.
Spreading a project across several threads only leads to confusion.
Leo..

MorganS

Run a higher voltage on the cable. 5V or 12V. The thin wires in many USB cables will give significant voltage drops. The higher voltage will reduce the current and the losses.

Then the different sensors can convert that voltage to their local requirements. +/-5V can be trivially generated from +5V.
"The problem is in the code you didn't post."

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