[KD8CEC] Creating a simple S-Meter Sensor for uBITX (LM358 Version)

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KD8CEC Amateur Radio

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Creating a simple S-Meter Sensor for uBITX (LM358 Version)

Posted: 27 Jun 2018 06:41 AM PDT
http://www.hamskey.com/2018/06/creating-simple-s-meter-sensor-for.html

Creating a simple S-Meter Sensor for uBITX (LM358 Version)
If you are already using S-Meter, you do not need to view this document.
This document is for those who do not have an S-Meter Sensor or want to use
some of the features using S-Meter on the Nextion LCD. 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.

uBITX Firmware CEC version is based on unmodified uBITX. However, to see
the strength of the received signal, you have to attach the sensor. Of
course, there is no problem in using CEC firmware without a signal meter
sensor. Most people I know have not installed an S-meter yet.



I was suggested to make an S-Meter Sensor using the LM358 which is a bit
cheaper than the LM386. This circuit is a modification of the basic form of
the OP-amp, which is very common. This model set the offset voltage to
0Volt. (The previous version using LM386 was 2.5~3Volt), So one more part
was added and five were used.

1. Parts list
LM358 * 1
1n4148 * 1
Resistor 1K * 1
Resistor 10K * 1
Capacitor 1.5nF ~ 40nF
(I recommended 1.5nF ~ 3nF if you use Nextion (or TJC) LCD )

2.Schematic
The LM358 has been rotated 90 degrees. attention to the Pin number.



3.Wire UP
The figure below is 'uBITX Wire UP' at hfsignals.com. I added a number to
connect to it. (Red color number)

http://www.hfsignals.com/index.php/ubitx-wire-up/

4.Test

I made it again with IC Socket.


Connect 1N4148 to pin 1
Connect 10k to Pin2 and Pin1
The pin numbers of the LM358 are shown in red.


Connect 1k to Pin2 and GnD
Connect C1 to GND and 1N4148


I have made it possible to replace the capacitors as shown below to do some
experiments.


It is the final finished.


5.Conclusion
Maybe if you use C1 at 1.5nF, the S-Meter may not be accurate.
In this case, if you replace C1 a little bigger, it will probably work
stably.
However, if you are using Nextion LCD or TJC LCD, we recommend 1.5nF. In
the next beta version, I will introduce some fun features using this
S-Meter.

My plan is to introduce one or two different versions of S-Meter in the
future.
It costs maybe $ 3 to $ 9, but it is not expected to be so difficult to
make.