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Capacitor Selection and Application of S-Meter in uBITX with Nextion LCD (Version 1.095 Improvements)

Capacitor Selection and Application of S-Meter in uBITX with Nextion LCD

This document is intended to illustrate some of the features added in CEC Firmware Version 1.095, Version 1.095 has been released. (
Several features have been added in Version 1.095, Most of the improvements will be covered in the deployment article.

1.S-Meter and uBITX Firmware CEC Version
uBITX CEC firmware is based on uBITX, which has not been modified.
but, In order to view signals from Character LCD or Nextion LCD, Signal Meter Sensor must be installed.
Of course, CEC Firmware operates normally even if S-meter sensor is not installed.

The S-Meter sensor is optional.

There are many ways to create S-Meter sensors. And most S-Meter sensors are compatible with CEC Firmware. Please refer to the link below for instructions.

uBITX CEC firmware must set values for S-Meter in uBITX Manager.
This is the method for using most S-Meter sensors.

2.Selecting a Capacitor for Use with the S-Meter
I posted how to make an S-Meter sensor using the LM358.

I wanted to make fun with S-Meter which can make 5 parts.
Most of these functions are only for Nextion LCD (include TJC LCD).

The basic structure of the S-Meter is to charge the capacitor with electricity and read the charged amount from the ADC.

I will explain how to select Capacito in S-Meter and the functions added in Version 1.095.

I made the capacitor as replaceable as shown in the picture below and observed the operation according to the capacitor.

To observe the variation of the ADC, we use ADC Monitor which is supported from Version 1.094.
Touch the 'CW Information Panel'

Touch the 'ADC Monitoring'

The figure below shows a graph using a 100nF capacitor (marked 104)
We can see that the discharge is slow even after the signal disappears.

The figure below shows a graph using a 10nF capacitor (marked 103)
Is there a difference from 100nF?

The figure below shows the graph when 0.3nF (marked 301)is used.  0.3nF may not be stable.

If it is used below 0.2nF, normal measurement may not be possible.

I decided to use 0.3nF on uBITX with Nextion LCD

3.Multi Band Scan
It is a function to scan the ham bands quickly. This makes it a little more convenient to find Active Frequency.
I do not know if this is useful, but it's fun.

Touch the S-Meter Graph

The following screen appears, this screen is band scan.
There are four buttons at the bottom of the screen.
If you want to scan 3Mhz, 7Mhz, 14Mhz, touch the first button. Or if you want to scan 7Mhz, 14Mhz, 21Mhz, touch the 3rd button.

There are three buttons on the right.
Press the button marked 'Exit' to return to the main screen

scan 7Mhz, 10Mhz, and 14Mhz for the experiment.
Touch the '7,10,14' button

After a while, the graph will be displayed as shown below.

It took me about 0.7 seconds to scan a ham band when I experimented. So I made it three scans per band. 

Let's check the scan results based on 14MHz.

In the figure above, there is a signal in the red squares

You can directly receive the frequency from this screen.
Touch the check box on the right (14Mhz Band)

The screen will change as shown below.

Try moving the slide
when the slide moves the frequency bar will move together, The frequency on the right will also change

You can receive the signal by moving the bar to the part where the signal is as shown below.

At this time, pressing the Apply button will set the received frequency to the current frequency and return to the Main screen

3.Spectrum Scan
This function is to scan adjacent areas based on current frequency
I'm not sure if this is useful either, but it's fun.

Touch the 'CW Information Panel'
Touch the 'Spectrum scan' button

You will see the following screen, This screen is Spectrum scan.
The current frequency is displayed at the top center of the screen
1397745 on the left is the starting frequency for scanning, You can see that the range is quite wide

Because the 1397745Mhz is not a ham band, the scan results will be useless
Let's move the center frequency a little bit.

You can move the center frequency by moving the slider in the upper right corner

If you set the desired frequency range as below, touch the Spectrum button

You can see the progress as below.

When all the scans are completed, the following graph will be displayed

You can listen to the measured frequency directly by moving the slide below.
Press the 'Apply & Home' button to return to the main screen after the currently received frequency is applied

The video below is an image taken to create this document. All examples are included

If you have an S-Meter sensor, please wait a day or two, Version 1.095 will be released.

Thanks for reading


  1. Thank you lan!
    You're doing such a great job. Your ideas and their implementation are always amazing. You are living the idea of beeing an HAM like it should be.
    73, Peter

    1. DerWossi

      thank you. The idea comes from other cool HAMs. I have not even heard of the Nextion LCD a few months ago :)

      Ian KD8CEC

  2. You are doing a great job. I did notice while reading, you repeat 100nf for both pictures, but the one picture (2nd one) shows actually 10nf capacitor. Just thought I would let you know for both pictures in the text you say 100nf. I can't wait to build my S-Meter circuit!! Again thanks for all this development you are doing and sharing with us. Juddie WD8WV

    1. Juddie

      Thanks for finding my mistake. 10nF is right as you confirmed.
      I hope your S-Meter will be completed successfully this weekend.

      Ian Kd8CEC

  3. HI ,
    What is that large yellow piece of shrink stuff you used to wrap around the entire s-meter device ?
    kevin rea
    lancaster, calif

    1. Kevin

      It's Heat Shirink Tube.
      Because it is used in many things, it can be easily obtained.

      Ian KD8CEC

  4. Ian,

    I'm a bit late, but built the S-meter/op-amp sensor. I think it works very well. But when I feed a signal from my old Rohde&Schwartz generator, the maximum ADC value I get is only 570.
    I never get more than 8 S-units on the Nextion display.

    Today I increased the op amp gain by changing 1 k resistor to 500 ohms (soldering another one parallel) and now the max ADC is 750, which I also put in Ubitx Manager's highest value box.

    What would the right way to get a +20 dB signal to deflect the s-meter to maximum?

    Thanks in advance.



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