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Hi Scott, Looking at the layout I have created a basic simulation model (see below). I am not sure what the turns ratio is, it looks to be more than 10, so I have assumed 12 for now. The schematic for the sbitx v2 shows a turns ratio of 15. I have used what diodes (Schottky) were available in the simulation tool.
To limit the voltage to no more than the PIC VCC (3V3), there should be a potential divider on the output of the SWR bridge. The table shows the results with 47k series and 33k to ground for 100W.  For 40W, you could try 22k and 22k, but not the on-board 22k as it currently is connected. I am assuming that the PIC code is using the VCC (3V3) as the reference voltage option for the ADC. 
The sbitx V2 bridge is probably okay without a potential divider at RF power levels up to 40W.
As Steve said it may be easier to measure the voltages out of your bridge and then adjust the resistors accordingly. It is probably best to try and achieve the full swing for your desired operating power levels, but they should not exceed the 3V3 VCC for the PIC.
It may also be necessary to add a capacitor on the potentiometer output (e.g. 0.1uF) at the PIC end to suppress any stray RF pickup. You make have to experiment with the placement of the potential divider, it may be best to have it at the PIC end, but this will depend on the ground noise etc.
73, Dave
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Hi Steve,
Again, thanks for the feedback.? I appreciate the notes.
I was going to build an external voltage divider but I hadn't figured out the values, yet.? I really like your suggestion to use a potentiometer.? There's no current to worry about so why not?? It's an excellent solution and I can probably dial it in closely.? I have a box of various sizes and chunks of PCB I can use to mount it.? Yeah, it will be a bit of a kludge but who cares?? As long as it works, right?
Thanks again and more later, Scott??
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Hi Dave,
Thank you very much for the study.? You guys are my heroes!
I'll cobble together your suggestions (along with Steve's notes) and report my findings in the next day or two.
Thank you again, Scott??
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On Sun, May 14, 2023 at 01:23 PM, Dave (G8PTN) wrote:
it looks to be more than 10, so I have assumed 12 for now
-20 dB isolation so 10, correct?
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Steve,?
How did you manage to compile. Im having problems problems with the wire library.
Juan
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Juan - are you using the ATTinyCore board support package from Spence Konde?
73; Steve, N3SB
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Hi Gary, Yes, I noticed the advert said -20dB coupling which would equate to 10 turns, but the 7V DC for 100W did not match, it would be closer to 10V and there looked to be more than 10 turns on the example shown. Provided the turns ratios match on both sides, Scott should be able to calibrate the bridge with a known power source/meter.
It seemed a bit odd that 50 Ohms was fitted on the FWD side (100//100) and 51 Ohms on the REV side. I assume it is to reduce the FWD resistor power dissipation under normal low SWR conditions, although the PCB would allow for 100//100 on both sides.
73, Dave
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Hi Dave , My bridge has single 51 ohm resistors on both sides. ?The picture I originally sent was a stock picture from their web site. I wrote and heard back from 60dbm.com. ?Paul Glazunov (UU0JR) is the engineer. ?He said there are 15 turns and simply said that I’d have to change some of the resistors. ?He really did not ?comment otherwise. He sent this schematic:  I'm going to respin my ATtiny85 circuit board to include voltage dividers and 0.1uf caps as suggested.? Adding the divider seems a bunch easier than trying to change the bridge components.? Plus, if I use pots, I should be able to "tweak" the range pretty easily. More later, Scott
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Thanks Steve! That did the trick.? Now its working.   Juan
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Juan - nice work. Congrats!
Did you use Farhan's circuit, or develop something of your own?
This is really begging for someone to develop a circuit board in KiCad so that there's a nice solution for all of us DE owners. Since the protocol is I2C, it would also work with the uBitx radios; possibly with a few more turns on the toroids because of the lower power output.
73, Steve, N3SB
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Steve,? It's the same circuit from the sbitx v2 schematic. Only difference is that I used 120ohm resistors because is what I had.  Juan?
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On Sun, May 14, 2023 at 12:41 PM, Scott KE8KYP wrote:
Hi Steve,
Yes.? And for the record, I feel kind of stupid for not verifying the input tolerence of the ATtiny 85 beforehand.? You even advised me that I might need to make adjustments.??
At 5 watts, I get 1.5V.
At 10 watts, I get 2.4V.
At 15W, I get 3.1V.
At 20W, I get 3.5V.
All measurements taken at the ATtiny 85 with an RMS meter on the FWD input, sBitx in CW mode at 7035MHz on dummy load.
The bridge output seems approximately double of what it should be for a 40W machine.? My thought is to adjust the 1K/22K voltage divider output of the bridge to about 22k/22k of half of the bridge output.
What do you think?
Hi Scott, I don't know what you mean by "RMS meter on the FWD input"? FWD is an output and voltage should be DC. How did you measure the power?? If I divide your stated power numbers by sqrt(2), then your DC voltages at FWD fit. e.g. 20W is really 14.1W.? 14.1W is 41.5 dBm.? With a 10 turn -20 dB coupling,? Vpeak is 3.76V? - ~0.25V* of the 1N5711 is 3.51V *The Vf of the diode is going to vary over the 90 uA to 170 uA range and very temperature dependent. ? 5W --> 3.5W = 1.63V 10W --> 7.1W = 2.41V 15W --> 10.6W = 3.01V 20W --> 14.1W = 3.51V You have the board, you can count the turns. Rgds, Gary
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Hi Gary,
There are 15 turns (confirmed by 60dbm.com).
My previous measurements were taken of the FWD and REV signals to the tiny 85 at the tiny 85.? I was making sure the 100W SWR bridge output wasn't overvolting the tiny 85.? It was exceeding Vcc if I operated into the 20W+ range.? That made sense since 60dbm.com's spec is the bridge will output approximately 7VDC at 100W.? The reason I took these measurements was to develop a external voltage divider to reduce the bridge's DC output to the PIC. My hope was to replicate approximately the same DC voltage range to the PIC as Ashhar's design.?
I fashioned two 100K pots at the tiny 85 to divide the incoming FWD and REV voltages.? I can now calibrate the watt meter in the sBitx but the SWR meter is pegged at 10.0 on a dummy load.? As I'm going through all this, I'm not exactly sure how the SWR function calculated.? My guess is the power calculation is taken from the FWD input to the PIC and SWR is a calculation of both FWD and REV.? Ideally I would think FWD minus REV equals the ratio but I know it can't be that simple.? If it is that simple then I might be able to adjust the REV pot to match SWR indicated with an external meter.
Does that make sense?? Am I lost?? Close?? What do you think?
Cheers, Scott??
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60dbm.com 100W SWR bridge interface to sBitx DE  100W SWR bridge schematic 
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Here is the VSWR formula:
VSWR=Vfwd+VrefVfwd?Vref
Where
Vfwd = the forward voltage reading
Vref = the reflected voltage reading
73
Evan
AC9TU
ere?
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That did not paste properly.? Try again ;-)
VSWR = (Vfwd + Vref) / (Vfwd - Vref)
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Hi Scott;
When the sbitx software sees a reflected voltage that is higher than the forward voltage, it will display a full scale SWR.
After you get the first pot adjusted so that the displayed power is correct, use your Ohm meter to measure the resistance from wiper to one end, then adjust the second pot for the same resistance. That should get you pretty close, assuming the sensor provides the same voltage levels for power in each direction.
73; Steve, N3SB
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Hi Steve,
That's just about what I was going to try.? I was thinking I could adjust the second pot to obtain the SWR indicated on my external meter but I think I'll start setting the two pots the same.? I'll then tweak as needed and check at different power levels.? My fear is, to your point, the two sensors will not equal.? It is always something.
Thanks, Scott?
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Hi Guys,
Well, I finally got it working.? I'm not exactly sure why this worked but when I accidentally reversed the FWD and REV connections at the ATtiny 85 interface, I got good power and SWR indications.
I checked and triple checked my wiring.? There are no mistakes. Unless the schematic for the V2 ATtiny 85 inputs are reversed (pins 2 and 3) or the outputs of the 60dbm.com 100W SWR Bridge are miss-marked, I'm at a loss.? Perhaps something with the way the coil of the bridge is wound?? I'm just not sure.
Anyway, it works great.? Thanks to Steve, Dave, Gary and everyone for their help. I learned a lot.
Thanks again, Scott
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Scott - This is excellent news! Congrats on getting the Power/SWR Sensor functionality added to the DE sBitx!
This now makes you an -EXPERT- in bringing this V2 functionality to the DE. I'm sure that Farhan is smiling with your closing statement: "I learned a lot."?
Fantastic!? Happy Dance!!
73; Steve, N3SB
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