Re: BITX QSO Night, Sunday, June 11, 7pm Local Time, 7277 kHz in North America, 7177 kHz elsewhere
N9ARZ was 59 here in Coralville, IA but didn't hear me. Maybe next time.
John AD0RW
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The relays are polarized type, they have a magnet inside to reduce operating current.
They wont operate with reversed voltage.
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At 12-06-2017, you wrote: The NPN's powered from the "TX" 12v rail do not get power unless the PTT switch is pressed to transmit.
I suggest you concentrate on the receiver first.
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Colour TFT + Touch controlled VFO/BFO
I have put preliminary information on my cheap Mcufriend 2.4" TFT based VFO/BFO with touch controls at vu2spf.blogspot.com
More pictures and program to follow. Soon I will be uploading its video too.
73
VU2SPF
SP Bhatnagar
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Re: Calling West Coast BITX operators
I had a QSO with Don ND6T in California about half
an hour early... my first one with someone using a
BITX40! I'm still waiting for my BITX40, so I was
running 100W. Don was fairly weak... about 43.
I later heard K7RTV, KG7UMW and N6QW although I
thought I heard him saying he was not QRP. I heard
ND6T again in a QSO during which he peaked up to 59.
There were quite a few weaker stations whose call
signs I couldn't copy.
--
73 Keith VE7GDH
CN88
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Reverse polarity protection is a must. I have always put a diode in my designs. Does not cost much.
First thing I did before powering up the BITX40!
Raj
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At 11-06-2017, you wrote: My curiosity overcame me. Pulled the LM7805 from my Raduino (so I was sure I was working with the same manufacturer that hfsigs uses) and verified proper operation with 12v in, saw 5v out. Reversed the 12v leads into the LM7805, put on the safety goggles, and powered up. Was powering from a 2.5 amp 12v supply. The reversed LM7805 was sucking enough current to pull down my 12v switcher to -5v going into the LM7805, saw -2v going out of the LM805. Could well be more than -2v going out if I had used a beefier 12v supply. Regardless, -2v is sufficient to damage some parts behind the LM7805. After a few seconds the LM7805 got hot enough to vent and stink up the room.
So, the LM78** parts offer little to no protection from reversed power supply leads. Not surprising, they were designed 40 years ago when such niceties would have been too expensive to include. A reversed power supply to the rig could easily blow the Nano on the Raduino. The Nano has an internal 3.3v regulator that may or may not save the Si5351, but no guarantees. The LM78L09 powering the analog VFO and LM78L05 for the IRF510 bias likely have the same issue.
The LM2940* family of regulators does offer reverse polarity protection and has a lower dropout voltage. However it is twice as expensive ($1.00 vs $0.50 from mouser for 10), they recommend at least 22uf on the LM2940* output to maintain stability. As mentioned previously, having an LM2940-12 at the main Bitx40 supply going into the board would protect us from reversed power leads, and also avoid trouble from supplies that exceed 12v such as a stack of 4 lithium batteries. The IRF510 should be powered separately, as we may want considerably higher voltages and currents there and the IRF510 is plenty cheap.
I am left very curious if Matt's Raduino is still functional. Does the display come up if you apply 12v to it?
Jerry, KE7ER
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Please see the link given below
Thank you 73 Ameer Khan VU3SQM
On 12-Jun-2017 7:42 AM, "John Smith via Groups.Io" <johnlinux77= [email protected]> wrote: Does anyone know if those cheap Usb sound card adapters offer any isolation between PC and radio? I plan to try out these things with my isolated interface for digital modes. The plan is to use an Usb to serial adapter for the PTT, and one of these sound card dongles for audio, and a Usb to DIP adapter (exposed PCB) to pick up power for a 5V relay module with opto isolation. All on a 4 way Usb hub. The object is to have one connection to PC. And just hoping I can get away without the audio transformers for the lines in and out.
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Re: BITX QSO Night, Sunday, June 11, 7pm Local Time, 7277 kHz in North America, 7177 kHz elsewhere
After weeks of trying I finally had some success! First QSO with Rick WB0NPM then Don ND6T. I also hear a few others but can't make them out. Rick mentioned an early net 8AM on 7186, may give that a try.
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I had one that looked similar to your Ebay post and it didn't have any isolation between the computer ground and the audio in and out ground. I did the VOX interface as well. I intend my Bitx to be mostly portable so I skipped the transformers in this one to save space and just added a resister and some caps to get some DC isolation. We will see if that was a mistake but it seems to be working fine as of now.
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I have worked with a lot of cheapy ones from aliexpress they wont have any isolation. I use a vox interface just for that. It does add more cables to the mess but it works.
Gl
73
David
N8DAH
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Does anyone know if those cheap Usb sound card adapters offer any isolation between PC and radio? I plan to try out these things with my isolated interface for digital modes. The plan is to use an Usb to serial adapter for the PTT, and one of these sound card dongles for audio, and a Usb to DIP adapter (exposed PCB) to pick up power for a 5V relay module with opto isolation. All on a 4 way Usb hub. The object is to have one connection to PC. And just hoping I can get away without the audio transformers for the lines in and out.
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Re: BITX QSO Night, Sunday, June 11, 7pm Local Time, 7277 kHz in North America, 7177 kHz elsewhere
I heard KD9CYF calling several times. I did not get a response.
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Re: BITX QSO Night, Sunday, June 11, 7pm Local Time, 7277 kHz in North America, 7177 kHz elsewhere
No joy here. ?Lots of noise.?
Doug?
KD9CYF?
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Re: BITX QSO Night, Sunday, June 11, 7pm Local Time, 7277 kHz in North America, 7177 kHz elsewhere
HAHAH - one of my two QSOs was you!
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Re: BITX QSO Night, Sunday, June 11, 7pm Local Time, 7277 kHz in North America, 7177 kHz elsewhere
It were noisy.
I, too, was late to the party - around 7:45 CDT.
I caught two:?
KG5KYJ - SIG 58 or so, BitX to BitX QSO! about 00:45 GMT
KF4WBJ - SIG 54 - could be incorrect, but I *think* that was the call about 00:50 GMT
Wish I'd gotten there earlier, but got busy.
I'll be there with bells on next week.
?
73
Mike Yancey, KM5Z
Dallas, Texas
On Sun, Jun 11, 2017 at 05:43 pm, John Smith wrote:
Well, I am late to the party but I was listening on 7.277 an came running to receive QRM on 7.276. Did we ever agree on a secondary? And I just heard W1LY LOUD and CLEAR trying to contact the QRM in progress. And they moved. de KG5KYJ.
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Re: BITX QSO Night, Sunday, June 11, 7pm Local Time, 7277 kHz in North America, 7177 kHz elsewhere
I heard KG5KYJ in MI but you did not hear me.
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OK, that last post does overstate it a bit.
Dropout through an LM2940* is not zero, it's around 0.130mv at the 150ma draw of the Bitx40 (excluding the IRF510)
With schottky power diodes, drop through a bridge rectifier might get down towards a half volt.
But I think the LM2940* is a win, especially since it limits the voltage to 12v and offers some over-current protection.
Yet another trick is the NDT2955 enhancement mode PFET that Steve Webber uses on the MTR series rigs.
Power from battery goes in on the drain, out on the source to the rig, a 5v zener from source to gate, a resistor from gate to ground.
The PFET's substrate diode conducts when power is first turned on, when there is 5v across the zener the transistor turns on
and does away with the voltage drop across the substrate diode. ?But nothing happens if battery leads are swapped.
More than you wanted to know.
Jerry
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On Sun, Jun 11, 2017 at 05:49 pm, Jerry Gaffke wrote:
With the bridge rectifier, you have two unnecessary diode drops. ?So a 12v battery might only deliver 10.5 volts or so to the rig.
The diode and fuse trick avoids the voltage drop, but is a rather brutal approach.
The LM2940* simply shuts down if battery is reversed with no voltage drop penalty, and provides over-voltage protection as well.
?
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With the bridge rectifier, you have two unnecessary diode drops. ?So a 12v battery might only deliver 10.5 volts or so to the rig.
The diode and fuse trick avoids the voltage drop, but is a rather brutal approach.
The LM2940* simply shuts down if battery is reversed with no voltage drop penalty, and provides over-voltage protection as well.
Jerry
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On Sun, Jun 11, 2017 at 05:25 pm, Dr Fred Hambrecht wrote:
Even better go through a fuse and have a standard diode between the fuse output and ground. If reversed the diode causes the fuse to blow. Another cure is to feed the input to a bridge rectifier and now it doesn¡¯t matter how you hook it up. I tend to use the bridge approach as the fuse seems to be blow right after the most expensive component in a circuit.
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Re: VK and ZL group buy of Jack W8TEE VFO boards
Count me in on 2 please
Regards martin? VK6FEEE
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Re: BITX QSO Night, Sunday, June 11, 7pm Local Time, 7277 kHz in North America, 7177 kHz elsewhere
Well, I am late to the party but I was listening on 7.277 an came running to receive QRM on 7.276. Did we ever agree on a secondary? And I just heard W1LY LOUD and CLEAR trying to contact the QRM in progress. And they moved. de KG5KYJ.
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I looked at figure 15 of the LM340 datasheet,
the "shorted input protection diode" is in parallel with the regulator, not in series with it.
The diode addresses a weakness of the LM340: ?if the input of the LM340 suddenly drops to zero
then the output filter caps will discharge through the LM340 to the grounded input pin, with possibly enough current
to destroy the LM340. ?I have not seen that recommended on any modern linear regulators, and doubt it is needed.
Likewise most regulators don't need a protection diode across the output as shown in fig 26
(Though I suppose it could help if the battery leads are reversed, and the regulator does not block reverse voltages
like the LM2940* does, and the diode is big enough to not burn out.)
However, "a 1N400x in series?with the regulator input" as Arv describes it is a very good idea if you can tolerate the diode drop.
That will protect the regulator and everything behind it from reversed battery leads.
Or you could use an LM2940* (pin compatible with the LM7805), which has reverse protection built in,?
but does not pay for it with a significant voltage drop across the device.
Jerry, KE7ER
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On Sun, Jun 11, 2017 at 10:28 am, Arv Evans wrote:
45 years ago in the LM340 regulator days it was conventional to always put a 1N400x in series
with the regulator input.? The problem of shorted regulators passing full voltage through them was
well known and accounted for with the series diode.? Somehow we seem to have forgotten that
knowledge over the intervening 40+ years.? Doing this means that you have to account for the
additional 0.65 volts of diode voltage drop, but it is a small price to pay for the added security.
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The datasheet also shows the shorted-input protection diode across the regulator device (Fig. 15)
and a protection diode across the output (Fig. 26).
Arv K7HKL
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Raj vu2zap
SP Bhatnagar
Jeff
N8DAH