ADC speed?

vbastani
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Joined: Mon Jan 30, 2017 1:41 pm

ADC speed?

Postby vbastani » Mon Jan 30, 2017 2:17 pm

I am interested to know more about the ADC speed but I couldn't find it. I would like to know:
  • what is the maximum speed (sample per second) of the ADC? or what is the speed vs accuracy trade-off?
  • are the ADC channels synchronized?
  • is continuous ADC reading available in the API?

I would like to read some sensor values at relatively high speed (e.g. 40 Hz). the phase difference between the sensor's signals are important so the sampling should be synchronized. is it possible using ESP32?

Thanks

ESP_puff
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Joined: Tue Jan 10, 2017 8:34 am

Re: ADC speed?

Postby ESP_puff » Fri Feb 10, 2017 5:59 am

Hello vbastani,
The sample frequency is 6KHZ. We have 12-bit SAR ADC up to 18 channels.

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kolban
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Re: ADC speed?

Postby kolban » Fri Feb 10, 2017 4:06 pm

Howdy,
Many thanks for the response. Can I assume that by saying that the sample frequency is 6kHz then we sample ADC 6000 times a second? Does that mean that there are 6000 results a second? If i was to be a masochist, then the minimum time I should read new values is 1/6000th of a second?

Does the bit width of my ADC configuration change the number of samples?
Free book on ESP32 available here: https://leanpub.com/kolban-ESP32

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rudi ;-)
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Re: ADC speed?

Postby rudi ;-) » Fri Feb 10, 2017 4:21 pm

ESP_puff wrote:Hello vbastani,
The sample frequency is 6KHZ. We have 12-bit SAR ADC up to 18 channels.


txs
Interesting would be still, all channels share this frequency or applies to everyone
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BaartCM
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Joined: Tue Mar 13, 2018 11:55 am

Re: ADC speed?

Postby BaartCM » Tue Apr 17, 2018 7:46 am

Hi, I have a vibration analysis project. I have been using the stm32f103 which can get high sampling rates with analogRead() and even higher using DMA but I want to go wireless and the ESP32 seems the logical step forward.

Whilst 6 ksps is ok for most of my application, Lubrication deficiency shows up as a broad band increase between 5khz and 15 kHz in the FFT spectra so a sampling rate of 30-40 ksps would be nice. I’d rather pick up a lubrication problem that can be sorted with a shot of grease than wait for a full blown bearing fault to become evident lower down the frequency scale.

Could this rate be achievable using dma techniques and has anyone done any work on it?

Fingers crossed, Steve.

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luisonoff
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Re: ADC speed?

Postby luisonoff » Tue Apr 17, 2018 8:13 am

Recommendation: use ESP32 + external ADC IC that meets your requirement

BaartCM
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Re: ADC speed?

Postby BaartCM » Tue Apr 17, 2018 10:20 am

Yes, I know I could use an mcp3208 and get higher sampling rates, I designed and sold an 8 channel board for the raspberry pi on eBay and got 100ksps no problem. It’s an option of course but if there’s any way the internal ADC can get a higher sample rate, why waste money?

bobolink
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Joined: Mon Feb 26, 2018 4:17 pm

Re: ADC speed?

Postby bobolink » Tue Apr 17, 2018 11:42 am

There seems to be a number of audio projects that sample up to 44.1 Ksps
Here is one that samples at 40 Ksps and does an FFT which seems to be what you want.

https://github.com/G6EJD/ESP32-8-Octave ... lay_03.ino

I don’t know if this sampling is continuous or they sample for a while, do math, then start sampling again.

ESP_Sprite
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Re: ADC speed?

Postby ESP_Sprite » Wed Apr 18, 2018 2:18 am

FWIW, as I understand it the 6KHz my colleague posted is an analog bandwith number. You can sample way faster than that, but we don't guarantee all frequencies will make it unattenuated into the digital samples.

bobolink
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Re: ADC speed?

Postby bobolink » Wed Apr 18, 2018 2:34 am

Where is the 6 KHz analog filter?
Is that the “Low Noise Amplifier” in the manual?
Can’t that be switched out?

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