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Arduino Based SWR/PWR Meter – The Board

I recently posted about a small analog SWR/Power meter I got from eBay, and figured it needed some improvement.

After some web searching I located a project by ON7EQ, an Arduino sketch to read SWR & RF power from any SWR bridge.
The Arduino code is on the original author’s page above, his copyright restrictions forbid me to reproduce it here.

I have also noticed a small glitch in the code when it is flashed to a blank arduino: The display will show scrambled characters as if it has crashed. However pushing the buttons a few times & rebooting the Arduino seems to fix this. I think it’s related to the EEPROM being blank on a new Arduino board.

I have run a board up in Eagle for testing, shown below is the layout:

SWR Meter SCH
SWR Meter SCH

The Schematic is the same as is given on ON7EQ’s site.
Update: ON7EQ has kindly let me know I’ve mixed up R6 & R7, so make sure they’re switched round when the board is built ;). Fitting the resistors the wrong way around may damage the µC with overvoltage.

SWR Meter PCB
SWR Meter PCB

Here’s the PCB layout. I’ve kept it as simple as possible with only a single link on the top side of the board.

PCB Top
PCB Top

Here’s the freshly completed PCB ready to rock. Arduino Pro mini sits in the center doing all the work.
The link over to A5 on the arduino can be seen here, this allows the code to detect the supply voltage, useful for battery operation.
On the right hand edge of the PCB are the pair of SMA connectors to interface with the SWR bridge. Some RF filtering is provided on the inputs.

PCB Bottom
PCB Bottom

Trackside view of the PCB. This was etched using my tweaked toner transfer method.

LCD Fitted
LCD Fitted

Here the board has it’s 16×2 LCD module.

Online
Online

Board powered & working. Here it’s set to the 70cm band. The pair of buttons on the bottom edge of the board change bands & operating modes.
As usual, the Eagle layout files are available below, along with the libraries I use.

[download id=”5585″]

[download id=”5573″]

More to come on this when some components arrive to interface this board with the SWR bridge in the eBay meter.

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LM386 Stereo Audio Amplifier

The quickest project from inception to working PCB yet:

From inception to a working PCB took only 4 hours!

LM386 Amplifier
LM386 Amplifier

This is a miniature stereo audio amplifier, 0.5W per channel, that can be run from any voltage between 4-12v DC.

As usual, all the Eagle project files are available for download below & kits/bare PCBs will be available for sale for those that cannot etch boards.

In Operation
In Operation

Here is the circuit driving a pair of 3W 8Ω speakers from a line level audio source. The gain of this circuit is set at 50 with the components specified.

 

Schematic
Schematic

As can be seen from the schematic, this is a pair of single LM386 ICs for each channel.

Gain can be set by altering R3 & R4

[download id=”5566″]

Buy Kits Here £9.50:
[wp_cart_button name=”LM386 Stereo Audio Amplifier Kit” price=”9.50″]

Buy bare PCBs here £5:
[wp_cart_button name=”LM386 Stereo Audio Amplifier PCB” price=”5″]

PCBs are etched on FR4 laminate with 8oz copper with top component silkscreen.