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Ultralight SWR indicator?


Thanks Martin. Unfortunately the somewhat critical Kingbright LEDs are not available from Mouser. I started creating a Mouser project (http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=7968437adc) to make it easy for folks to order a kit of parts but it lacks the Kingbright LEDs (and the enameled wire).


Thanks! As for the LEDs: Maybe other 2mA LEDs will work as well if they have similar forward voltage and a sufficient brightness at low currents.


What did not work well were these:

I think that for my first variants, I used very unspecific “bulk” red LEDs and that worked quite okay.

The replacement should have a forwards voltage of typical 1.7, max 2.0V.

I would search for 2mA versions. Maybe the following ones will work:


I would order a few types and try.


Thanks Martin. I’ve updated the Mouser project at http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=7968437adc to include 3 different types of red LEDs for experimenting. The project is complete except for the enameled wire, which Mouser doesn’t sell in small quantities. The other thing folks will need, besides the PCB, is a method of connection for RF IN/OUT. I guess some thought should also be given to whether to enclose it or not, i.e. how to make it more physically/mechanically robust to survive field activations.


Thanks, Barry! I added a link to your Mouser BOM list to the GitHub repository.

Builders from Germany will very likely get all the parts from Reichelt. If you anybody does so, it would be kind to create a respective list and share it (which can be done via the MyReichelt link on the top of the page).



I added 50-ohm and 100-ohm 5W resistors to the project - for calibration at SWR 1:1 and to see what is displayed at SWR 2:1


Thanks Martin and Barry for links and all that work.
Parts ordered here to build my version. I’ll give a feedback whenever assembled and tested!



Martin, the link up at GitHub to the Mouser project is wrong. It should be https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=7968437adc and it shows something else.

73, Barry N1EU


Dear Barry,
thanks for spotting! I just fixed it.
By the way, I got my PCBs from OSH Park a few days ago, but I did not yet find the time to try them out.
73 de Martin, DK3IT


My boards (from Osh Park) came in Saturday and the Mouser order arrived a few days ago. I bought the parts using the list. Hopefully I used the right list. I haven’t had a chance to assemble or test it. I hope it works :slight_smile:

73 NE5U



I assembled a first prototype of the new PCB over the weekend - it is complete except for the trimpot, which arrived today. I won’t have time to test the entire design until next weekend, so if anybody else was already successful, I would appreciate a short post. I would be very surprised if the new PCB had any errors due to the ERC check, but you never know.

Martin, DK3IT


I just built two of the Tiny SWR boards. I gave one to a friend of mine otherwise I would have built all 3. Except winding the toroid. As near as I can tell 0.2mm magnet wire is equivalent to 32 AWG. I have 30AWG on hand. I have 32 AWG ordered and it will be here tomorrow. Almost there :slight_smile:




Thanks, Mike!
I added the trimpot to my first attempt of the new TinySWR PCB. I only had a few minutes to test this before leaving for a business trip. During that quick test, I could not get the display below two LEDs against a 50 Ohm dummy. I will have to investigate this; it might just be sloppy winding of the toroid or a minor flaw in the PCB, or a misplaced component.

I will post my results as soon as I got the time to analyze this. Should there be a mistake in the PCB layout, it cannot be major and should be fixable with ease, but for the moment, I assume I just misplaced a component.

73 de Martin, DK3IT


Hi Mike, all:

There is indeed a small problem with the V2 PCB: The GND signal between the actual circuit and the antenna / rig connectors is not connected (because that missing link was hidden behind a junction in the schematic, so the ERC/DRC did not spot this).

I think that adding a short wire from the ANT GND (the rectangular pads) to any of the other pins that should carry GND (e.g. GND side of R3, R4, R5; cathode pins of SWR3 or RF1, or anode of D3) should do the trick.

Will try when back.

Sorry for the inconvenience!

73 de Martin, DK3IT


Ok, I think I fixed this with a new version of the PCB, which is available from OSH Park at

The Github repository is also now up to date:

I have not yet been able to test the fix I described, but I am pretty optimistic that a single jumper wire from GND to the GND side of the SWR detector circuit will fix the problem.

The new version includes a few additional improvements (10mil instead of 6mil where space permitted, connecting the third pad of the trimpot, etc.). The schematic is unchanged except for cosmetics. The BOM is also unaffected.

73 de Martin, DK3IT (currently in SV5 land)


Ok, I have been able to confirm my suspicion: Indeed, there is a missing link from the GND net of all the components to the GND of the ANT/RIG connectors. Fortunately, there is an easy fix for this:

The recommended solution is a short wire from ANT GND to the rectangular pad of the yellow LED labeled RF1. The picture below shows this modification. Be careful not to shorten the “RIG” GND pin with the RIG signal pin.

One surprising thing with this version of the prototype is the fact that the minimum (all LEDs off) is in the middle of the trimmer potentiometer, not on one end. It may be that the windings on my toroid are a bit sloppy.

But anyway, the indicator works as intended with this modification.

Once the PCBs for the third revision will arrive, I will build another prototype.

73 de Martin, DK3IT


Hi Barry. I got the PCB and the parts from Mouser.
Today I started building up and I miss one component!

Diode D1 is listed as SMD 2115 / 0805 - Red, Forward Voltage min: 1.7, max 2.2, typ 1.8 V - MPN: OSRAM OPTO LS M67K-H2L1-1-Z in the listing created by Martin.

Nevertheless, the parts I got from Mouser are all but this component. Did you updated the listing with it later, after the start of the project?

i think I’ll get it from Reichelt now… Look forward to finish soon…

Thanks, 73 de Ignacio

Ps: It is really tiny!!!


Hi Ignacio,
as far as I can see, Barry’s BOM includes the diode for D1. The Mouser part number is


It is the 5th line in Barry’s list at Mouser’s.

If you miss it, you could try any other 0805 red LED, it could still work. Or try to squeeze in a standard 3 mm THT LED in red; that should have a better match wrt to its forward voltage.

Best wishes



PS: Do not forget to add the missing connection to fix the bug in the 1.1 release of the PCB, i.e. that the connection between the ground of antenna and rig on one hand and the SWR circuit is missing. Adding a short wire from the ANT GND (the rectangular pads) to any of the other pins that should carry GND (e.g. GND side of R3, R4, R5; cathode pins of SWR3 or RF1, or anode of D3) should do the trick.


Thanks Martin,
yes I’ll fix the bug on the PCB. It looks very nice,

Excuse me Barry, I just double checked and found the M67K on the box!!!
Now I can finish the assy.

I’ll give feedback here whenever I can put In / Out connectors and test it .

73 de Ignacio