RP2040 Maximum Sample Rate Setting - Scoppy - Oscilloscope and Logic Analyzer.pdf

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22.07.2024, 13:28

RP2040 Maximum Sample Rate Setting | Scoppy - Oscilloscope and Logic Analyzer

Scoppy - Oscilloscope and Logic Analyzer

RP2040 Maximum Sample Rate

Setting

This feature is only available in version 1.030 (or higher) of the Scoppy Android app when

version 17 (or higher) of the firmware is installed. Version 1.030 of the Android app will be

available soon. The latest firmware can be found

here.

About

The RP2040 datasheet states that the clock source for the built-in ADC must be 48MHz and

that each ADC conversion takes 96 clock cycles. This gives a maximum sample rate of

500kS/s (ie. 48000000 / 96 = 500000). This in turn limits the maximum bandwidth achievable

by a Scoppy oscilloscope

However, if we ignore the datasheet and clock the ADC at a higher rate then we can achieve

sample rates of up to 2.0MS/s with negligible affects on performance. The setting described

here allows us to do just that.

The Scoppy Android app allows us to choose from 3 different values for the maximum

sample rate. They are:

500kS/s - The default - the ADC is clocked at 48MHz

1.3MS/s - The ADC is clocked at 125MHz

2.0MS/s - The ADC is clocked at 192MHz

How to access and modify the RP2040

Maximum Sample Rate setting

From the

tap the

SETTINGS

button and then tap

RP2040 SETTINGS

and then

Max.

Sample Rate.

Tap your desired setting and then OK. The new maximum sample rate setting will take effect

within a few seconds.

FAQ

https://oscilloscope.fhdm.xyz/app-help/rp2040-max-sample-rate-setting

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22.07.2024, 13:28

RP2040 Maximum Sample Rate Setting | Scoppy - Oscilloscope and Logic Analyzer

Does changing the maximum sample rate affect the

accuracy of the oscilloscope?

We have found very little difference between the 3 available sample rates. However,

performance may depend on the analog front-end used to drive the ADCs of the RP2040.

See results of our testing

here.

Will the ADC perform as per the RP2040 datasheet

specifications at the higher sample rates?

Unlikely. The higher sample rates are outside of the recommended range specified in the

RP2040 datasheet and so the specifications stated in the datasheet will not apply.

Does this setting affect the Logic Analyzer?

Changing the maximum sample rate to 1.3MS/s will not have any affect when using the Logic

Analyzer mode. The 2.0MS/s setting will increase the maximum Logic Analyzer sample rate

from 25MS/s to 38MS/s.

Is the setting stored on the RP2040 (flash) or the Android

app?

The setting is stored in the Android app and so it will need to be modified on each Android

device.

What is the maximum sample rate when two oscilloscope

channels are enabled?

When both channels are enabled the maximum sample rate is halved. The maximum sample

rates for the three possible settings are thus 250kS/s, 625kS/s and 1MS/s when using two

channels.

Footnotes

This

only applies when the Scoppy firmware is running on an RP2040 and is sampling using

the built in ADCs. Future versions of the firmware may become available that either use an

external ADC or target different MCUs.

RP2040 Maximum Sample Rate Setting - Scoppy - Oscilloscope and Logic Analyzer.pdf

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