I am developing IoT device using ESP32.
I am using ESP32 along with ADS1115 for voltage measurement of my equipment.

My electrical device operates with following parameter : ~0-5 V DC , 25 Amp with constant current mode adjustment prior to operation.

I want to measure this voltage change across my device. I am planning to use voltage divider to sense voltage.

1.Can I use configuration as per attached picture?

2. Do I need to isolate my device+ Voltage divider and ESP32+ADS1115 circuit ? If yes then how shall I isolate it?

 

hi B700
Welcome to AAC.
Have you considered using the ESP32 onboard 12Bit ADC.?
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hi B700
Welcome to AAC.
Have you considered using the ESP32 onboard 12Bit ADC.?
E

Thank you for reply.

ESP32 onboard ADC is not accurate and stable enough for my application.

With ESP32+ADS1115 I am getting 2 decimal point accuracy.

My question is about isolation. Since my electrical device and ESP32 are fed from different voltage sources, I am wondering if i need to isolate two circuit or not.

 

hi B,
Do all your devices share a common 0V line.?
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hi B,
Do all your devices share a common 0V line.?
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Red Block is fed by High current power supply.

Black block is Fed by battery.


Both are floating power supply.

 

Hi,
Is it like this.?
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Hi,
Is it like this.?
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View attachment 285433

Yes , this is what I am my planning.
I am planning connect both 0V.

is it advisable to do so ,. considering two different floating voltage sources?

 

hi,
So, providing all the devices share the same 0V/Common, the resistive divider will work.
What are the divider values.?
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hi,
So, providing all the devices share the same 0V/Common, the resistive divider will work.
What are the divider values.?
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Not yet decided. But somewhere around 10K and 19K to not to overshoot 3.3V at ADS1115.

 

hi,
Those values will OK,
Is the 5V under test electrically 'noisy'.? And can the voltage ever exceed say 5V
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hi,
Those values will OK,
Is the 5V under test electrically 'noisy'.? And can the voltage ever exceed say 5V
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Power supply in red box is harmonic noise free supply. I'll be putting over voltage diode protection.

 

With ESP32+ADS1115 I am getting 2 decimal point accuracy.

Then why is 12-bit, 3 digit+ accuracy not accurate enough?

 

Then why is 12-bit, 3 digit+ accuracy not accurate enough?

Thank you for your reply.
Hi I don't have problem with accuracy.

My question is , can I have common 0V line for both of my circuit? Or do I need to use isolator between 2 circuit.

 

Then why is 12-bit, 3 digit+ accuracy not accurate enough?

Read about the skewed voltage vs count of the ESP32 and you may understand. Also, the device the OP selected is 16-bit. So, if he specified it, paid for it, let's just assume he wants or needs 16-bit of reasonably linear resolution.

 

My question is , can I have common 0V line for both of my circuit? Or do I need to use isolator between 2 circuit.

Hi B,
I have already answered your question in post #6.

With ESP32+ADS1115 I am getting 2 decimal point accuracy.

16Bit resolution ie: decimal 65535 for a 5V conversion is 5/65535=78uV/Bit, do you really need to resolve to this value.?
A Resolution of 78uV does not mean an Accuracy of 78uV

E
BTW: Can you say what the Device is within the Red box.?

 

Hi B,
I have already answered your question in post #6.



16Bit resolution ie: decimal 65535 for a 5V conversion is 5/65535=78uV/Bit, do you really need to resolve to this value.?
A Resolution of 78uV does not mean an Accuracy of 78uV

E
BTW: Can you say what the Device is within the Red box.?

Yes , I am aware about difference between accuracy and resolution.

Device is some special kind of DC motor. I am also not fully aware about it as this is some kind of confidential device.

 

hi B,
Reason for asking about the 'Device' is it possible that the addition of your divider load, may affect the open circuit PD voltage of the device.?
For the resistive divider, it would be a good idea to change the 19K resistor in the Post #10 divider to a 18K and add a 2K, 20 turn trim pot.
I will be then possible to trim the output of the divider.
E