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Creating a simple S-Meter Sensor for uBITX

Creating a simple S-Meter Sensor for uBITX

There are various ways to attach S.Meter to uBITX. You can find things on the Internet that are far superior to what I have created.

1.Parts list
1N4148 * 1
LM386  * 1
Capacitor (1nF ~ 40nF) * 1
  (Marked : 1nF : 102, 1.5nF : 152, 40nF:403)
  I Used : 1.5nF (152)

Resistor (4.7k ~ 20k ) * 1
  I Used : 4.7K

Capacitor 10uF * 1 : Option
  (I did not use it to use minimum parts, but if you have an extra 10uF, please use it.)

Capacitor and Resistor have different display type of S.Meter depending on values.
The larger the capacity of the capacitor, the slower the S.Meter moves from High to Low. I used 1.5nF (152) because I need to move quickly for testing.

It is the simplest model of the LM386.

The reason for choosing the LM386 is because it is cheap and the operation is reliable.
You will be able to buy at an internet shopping mall for less than $ 0.2.

Maybe you can find some of them around you. I was able to find some around after ordering the LM386 to Aliexpress.

I did not use a PCB because it was a simple circuit.
It is decided to attach directly to IC socket.

Minimal operation is possible by attaching only two parts like this.

Finally, one resistor is added. S.Meter sensor make is over.
Is it too simple?

This is my final project. (bottom side)

I installed the LM386. (top side)

Now you can mount it in uBITX.
There are several places to connect GND to 5Volt.

Pin 3 (Green Line) is 5 volts at the Raduino connector.
Pin 4 (Yellow Line) is GND at the Raduino connector.
Pin 1 (Purple Line) is A7 at the Raduino connector.

Pin 4 (Yellow Line) is VOL_HIGH at the Audio connector (on uBITX Main board)

It is better to refer to below.

After all connections are completed, set the following.

It is the simplest model of the LM386.

The following is recommended for the LM386 circuit with a 10uF capacitor added.

There are many ways to create S.Meter sensors. Posting here is just an example I used.
In uBITX, the voice signal is more than 0Volt, so the number of parts is reduced.
You can add your own parts to this circuit.
Note that the Arduino should have enough current to use the ADC. 


  1. Where can I download uBitx manager V1.05, and firmware V1.074

    73 Philip G7JUR

  2. Very good job Ian!
    Thank you!

    Paolo IW6BET

    1. Paolo

      Thank you for your attention.

      Ian KD8CEC

  3. Hi Ian.
    S-Meter now calibrated from S4 to S9+20 in 10dB steps.
    Using my own AGC circuit, ADC values 0 at S4 thought to 98 at S9+10. S9 being 73dBM.
    Great work, thank you.

    73 Philip G7JUR.

    1. Philip

      Thank you for test.
      I have not installed the AGC yet, but I am going to install the ND6T AGC.

      Ian KD8CEC

  4. This comment has been removed by the author.

    1. Hi~ KD8CEC

      Very simple

      Thank you

      Keydalee DS2BXI 73..

  5. This comment has been removed by the author.

  6. My S Meter is done and working. Used an LM386 module from
    Greg KG4GEK

    1. Thanks for good information.
      if using lm386 module, perhap we very simple added S-Meter to uBITX.
      this is very easy way.

      Ian KD8CEC

    2. Here is what I used. I ordered it on amazon, 5 pieces. Giving a couple to friends that are building.


  7. Where do you guys get parts from for these little projects?

  8. Thank you so much for sharing these modifications. I saw you latest blog on making an S-Meter and you had mentioned using the LM386 and I was hoping you would share that information. Didn't know you had done one. I plan on making one here as soon as I get my enclosure completed. Again thanks for all the great things are doing with the uBitx!!

  9. i want to use arduino to measure the swr but in tx mode the bargraph gets locked please help

  10. how about connecting A7 from any AGC

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