can i fit a nextion display to a v3 ubitx ?
73 pete G4HAK

thought this might be useful
have a ?ubitx v3 which was working great exept mic gain was v low. had a power mic DM510U handy so wired and connected it. put a 2mfd blocking cap in series with mic input line. works a treat and can control mic gain with var resistor already built into the mic. simples. and saved all those component changes!
all the best

Hello everyone.? I've assembled two uBitx v5's and was able to send and receive messages on JS8Call by putting a wire directly between the two.? I'm running the newest CEC firmware.? I also have CAT control and my audio interface is a simple USB sound card.

I purchased an antenna so I can try to receive messages in JS8Call from other hams.? The antenna is a Tram 3500 which is a CB antenna and should work fine for the 10 meter band based on my research.

I connected the shield of the antenna to the black wire, and the signal to the grey wire.? Loaded up JS8Call and nothing.? Maybe there's just nobody transmitting?

Unfortunately I don't have the second radio on hand to use for testing.

Then I disconnected the antenna and to my surprise there was no change on the waterfall.? I'm a beginner but that doesn't sound normal to me.? Here is a screenshot half of the waterfall is with the antenna plugged in and the other half is with the antenna unplugged.



I guess I have two questions.

Is there something wrong with my radio?

Are these not radio signals on the waterfall?? Is it just electrical noise?

Thanks!

Will definitely keep you in the loop with my progress.

Were you envisioning a dynamic mic with this, or electret?? I'm planning on putting together a little electret mic driver, but then I was thinking, could I just use the bias from the PTT circuit???? But I guess that would be a pretty low voltage (0.9V?) available there at the junction of R3 and D1, so probably not enough to drive the electret element...

/g/BITX20/files/V6_PCB_Photos/uBITX_v6_PCB.zip

^ There's a picture that was uploaded on another thread. Is that not precise enough for your needs?


Reed

Hi all, does anyone know the *exact* dimensions of the v6 board incl.?protrusions (for case selection ;-)?
Thanks to all!
KR Alfred

Hi Rob,

Yes regarding the blend control that was what I had in mind.

Regarding feeding 12V to the circuit and connecting the PTT via the diode it should work fine as the Arduino sketches I have seen use the digitalread function for the PTT (although it is an analog input) and therefore will read a logical zero for anything below 2.2V (at 5VDC supply).

BUT, if you feed the circuit from the boards' main supply I would decouple the DC biasing voltage very carefully with resistors and capacitors otherwise you could have bad feedback through the variations in supply voltage.

Personally I would stick with 5V (or anything regulated below your supply line voltage) and well decoupled. Remember the audio voltage to the mic input is normally in the tens of millivolts so a) you don't need more than say a volt to be quite safe from spurious diode conduction and b) small variations in supply voltage will happily feedback in your mic input signal. Just my 2 cents.

Happy home-brewing.

Let us know what you come up with please.

73, John (VK2ETA)

John,

Thanks for the schematic!? That all makes sense to me, and it matches the math in your previous post, so I appreciate putting a picture to the words.

I know in the past I have connected my sound card output directly to my mic input without a trim pot any sort.? But I also haven't done any of the TX preamp adjustments to my uBITX that I've seen, so perhaps my audio, even if higher than the mic, was still fine getting into the TX stages.

As far as (potentially... haven't made my mind up) removing R1/R2 and replacing D2 with a trimpot (essentially a blend control, is what I think you are proposing?), I'd actually considered using an op amp mixer to blend the two inputs.? Your version would certainly be simpler.

If I wanted to ensure I had headroom for higher amplitude audio signals, could I replace the +5V with +12V?? Here's my thought.? Down where you have the Mic PTT, of course switching that to ground is how the PTT would work.? But, I was thinking I could have a diode connected between the Raduino and the switch.? The cathode end would be connected to the top of the switch, as would the "Mic PTT" input in the schematic you created.? Voltage present when the switch is open (+12V I think) wouldn't exceed the reverse voltage of the diode.? When the switch is closed, that would ground out both the Raduino PTT pin (via the diode) as well as the Mic PTT line in the circuit above.? Forward voltage drop across the diode would still land me in logical-zero land for 5V logic.? ?I'm sure I'm missing something here, but it makes sense in my head...

Thanks again for putting this together!

Regards,
-Rob KC4UPR

Hello Rob,

Replying to your first question: a mic output is generally in the 10s of mV. On top of my head I have 50mv as a typical mic input voltage for radios, so 100mv was king of a safe value for a mic output.

This means you will have to reduce the audio voltage from your computer line out (a trim pot would be the easiest).

Here is a hand sketch based on you new requirements. Only difference in that circuit is that it will cut the computer audio when the mic PTT is pressed.

I think that is better as it prevents sound card noise and other feedback from the computer audio circuit.

If you want to mix the computer audio with the audio coming from the mic, remove R1, R2, substitute D2 by a resistor (100K trim pot?).

I haven't built that circuit yet, so it is purely theoretical at this point.

73, John (VK2ETA)

Hi,

There are several reverse polarity schemes that can protect the radio from damage in a reverse polarity episode. That is an episode of connecting DC power source with the positive and negative switched. Those are worthwhile to protect the radio gear. Any of us could do that at any time. That is not what fuses are for.

Reverse polarity is not the only thing that causes excessive current flow (shorts). The reverse polarity scheme is not going to keep an overload from burning your house down - maybe with you in it. An appropriate fuse will. They are cheap and easy. Cheap too, Easy too. Inexpensive, too. Uncomplicated, too. Is that clear enough? Please install fuses so we won't have to read about your untimely status as a silent key. Go ahead and operate without reverse polarity protection if you desire. It IS your gear.

73,

Bill KU8H

--
bark less - wag more

I would say the diodes you saw were to prevent any signals greater than the forward bias voltage, rather than signal routing.?
--
73
Dave

I have refined my requirements a little.

- The default input (enabled, even if neither PTT line is activated) is the computer line-in.? Why?? So that I can do PTT via CAT control if desired.
- However, the mic input can only be active if the mic PTT line is activated.
- I trust the computer to be quiet while the mic is in use.
- Mixing the two inputs may be desirable (i.e. if the mic PTT is being depressed, it might be desirable to also inject something via the computer line in).

Thus, the only input line I need to be able to switch is mic input, using the mic PTT.? While that input is enabled, the computer line in can also remain enabled.? I think this will greatly simplify the transistor/diode logic I need to implement...

Rob KC4UPR

John, you mentioned 100mv for the audio signals, is that ballpark for both computer audio and mic audio?? I guess I'd assumed it was around 1 V p-p or line level or somesuch.? But I haven't measured it.? Is +/- 100mv what I can expect for both sources?

开云体育

--

…_. _._

Ahem -- You can take Bill Cromwell's guidance to the bank.?

I used a 3amp fuse, and discarded the diode.? The way I figure it, every single power source in my house (and my zip code) has center pin positive (+) and the sleeve or shank or outside is negative (-).? So I have no fear of reversing the power.?

But I do have well founded fear of screwing things up, so the fuse is essential protection from fat fingering, lapse in judgement, intemperate decision making, lack of impulse control, or nature's choice of the moment to humiliate you (me).? If there is a wire or screwdriver or plug that can go where it shouldn't, then the cosmic forces of nature will ensure it goes there. It's like my daily dose of humiliation.?

So fuse up and get on the air.

By the way, when you get there, your uBITX is a perfect radio to send digital (sound card-based) modes. The native 10W will do wonders to get your around the world when conditions are good.

Don
km4udx

I will second Bill's assertion.? A fuse does not prevent the magic smoke from leaving your radio, though it's blowing "might" mitigate further damage if you're lucky.

A fuse keeps your house or car from suffering the same fate as whatever went wrong in your radio.? Period.? FWIW, I use a 4 amp in my field build and a 6 amp in the mobile [with 20 volts on the finals].

Ted
K3RTA

Rechecked and it will not work reliably.? Will need to look at it some more.? As stated, I just did a quick? sketch.

Sorry,
73
Evan
AC9TU

Rob,

I was following the examples in the attached.


Not sure if that will work moving both of the diodes to a single resistor to Vcc, however it is just slightly different from the 2 resistors with positive voltage switching.? Again, not sure if it will work, I would breadboard and try first.

73
Evan
AC9TU

Hey Evan, thanks for the quick response.? I follow the logic of the NAND gate, and also the forward biasing.? What I'm confused about is the reversing biasing, i.e. turning off a given input.? My thought is that when a given input is supposed to be off, the corresponding diode needs to be reverse biased, but I don't see that happening.? Or are you assuming that the forward voltage drop across the diode will be sufficient to block that input?

Thanks again!
-Rob KC4UPR