Analogue S-meter using a VU meter and driver module

Jean-Luc F6HOY added an analog s meter to his first BITx40 with a simple circuit on an audio line and a 500 microA vu-meter.  All was fine except that without any AGC it only provided an indication of the signal level.

Jean-Luc added a Chinese Audio Vu-meter that is much better on his µBITx.
For around 15€ he received a circuit module and 2 vu-meters.   Only one vu-meter is used of course.   The circuit board functions as an AGC, and for an extra bit of fun he has a nice warm light in the shack from the yellow light of the VU meter.

You can get this kit from several shops in China (one such  example).


Simulated S-Meter and SWR meter on small OLED display





Duwayne KV4QB has been playing with an Arduino Pro Mini and a small OLED display to use as a stand alone replacement for a analog meter.  The existing Raduino in the µBITx does not have sufficinet spare analog input pins to provide everything that Duwayne wanted to measure.

More information can be found on his blog at:

He is also working on a small board to provide forward and reflected power readings for SWR metering and power measurement.

This has created a bit of interest on the list, and represents an interesting idea that is potentially adaptable to other projects and use cases.


Using 2nd channel of TDA2822 for S-meter

John VK2ETA suggests using a section of the original AGC circuit of the µBITx (design by Ashhar Farhan VU2ESE) for generating a signal for an S-meter so that this can be used by his modified software.

This was part of the pre-production uBitx diagram but was not implemented in the production version.

The 2N7002 is used as an automatic gain control and can be used or not for that application.   The circuit has limitations since it was not included in the production version.

You would need to insert a trim-potentiometer (10K ohms is good) between pin 6 of the TDA2822 and the VOL-H connection to adjust the sensitivity, plus (VERY IMPORTANT) a voltage divider, between the cathode of the diode and the ground, to limit the voltage to under 5VDC for the analogue input of the Raduino.

John would use 330K ohm in series with 100K ohm to the ground, and connect A7 to the junction of the two resistors.

Further adjustments are available in the software if required as we define the 9 stages of the S-meter display (first stage is zero, then 6 stages for growing bars, 1 stage showing “+” and one stage showing the custom “++” symbol). In ubitx_20.ino it shows as:

int sMeterLevels[] = {0, 5, 17, 41, 74, 140, 255, 365, 470};

The values in the array are the measured values on the analogue input (defined as A7 above) at which we step into a higher “stage” and can go from zero for zero volts to 1023 for a 5V DC value.