I build myself a BITX 20, which can run up to 7W, and for that purpose I needed a small QRP SWR meter.
I decided to build one myself, so I took a visit to my god friend Google.
There are a lot of good ideas, and I ended up with a Arduino NANO and a 16x4 display, because I already had those parts.

KN9B had laid up a sketch, which I changed a bit from LCD 20x4 to 16x4 and direct connection of the display instead of using IC2, (there are plenty free pins on the NANO, so no problem).
Because it is a rather small program, you can use a 168 NANO, which are cheaper than a 328.
The bridge I am using is a Stockton bridge. (fig 1)

Fig 1

Normally the Stockton bridge uses two coils, but to minimize space I decided to try with a multi-aperture core from an old wideband power amp.

Connecting the bridge to the Arduino is just 2 wires and ground, so it is easy done, only problem is if the wires has been switched, but it is easy to see when the meter is running.
After putting everything together, the big moment came, would it work?
Yes, it acted precise as I wish. The size of the meter is 12 x 6 x 4 cm, which is pretty nice.

I have no switch on/off button on it because I drive it with the power to the radio.
If one wants to use it on higher power, the resistors R1 to R4 must be at least 2W each.
The two resistors in parallel are at 100 ohm each, to obtain 50 ohm.

The way I have put the pins between display and NONO is caused by the needs I had to put it all together in the box, and can be changed in the sketch if needed.
The same goes for the wires to A6 and A7, but do not use A4 and A5

The sketch can be downloaded from here: oz6yk16x4

 

Sources:

https://www.giangrandi.org/electronics/lw-swr/lw-swr.shtml

https://sites.google.com/view/kn9b/digital-swr-meter