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On 5/6/21 12:48 PM, jerry@... wrote:

On 2021-05-06 09:38, Bill Gunshannon wrote:

One small nit...? BAUDOT does not have upper and lower case.? Uperr
only.? The shift weas for non-alpha characters.

*** Yes, indeed.? I had forgotten, it was a long time ago.? Around 1970. ?I had a railroad surplus model 15. Which had no case.? To say it was loud would be an understatement.

I had a Lorenz LO-15 and really miss the sound. :-)

bill

On 2021-05-06 09:38, Bill Gunshannon wrote:

One small nit... BAUDOT does not have upper and lower case. Uperr
only. The shift weas for non-alpha characters.

*** Yes, indeed. I had forgotten, it was a long time ago. Around 1970. I had a railroad surplus model 15. Which had no case. To say it was loud would be an understatement.

- Jerry

bill

The failure mode on your RTTY terminal is similar to that of applying a signal in the threshold region?
to a logic gate:

> Some extremely high powered logic parts (74ASxxx family parts, I'm looking at you) can overheat
> and/or oscillate when an input signal is in the transition region between logic 1 and logic 0.? This is
> why it is good practice to tie unused logic inputs to a solid logic 1 or 0 (typically to ground).
> Many parts have some hysteresis designed into the input buffers, mostly avoiding this issue.

Typically an issue only on really high power parts,
careful design can usually avoid this.

Jerry, KE7ER

On 5/6/21 12:31 PM, jerry@... wrote:

All,
? Here's a real world example of damaging undervoltage:
I once built a RTTY TU ( Terminal Unit ).? The teletype had a "loop" consisting of a 120VDC power supply feeding a resistor and going to the selector magnets.
I used a high voltage transistor to switch the current on & off in time to the incoming baudot data.? Baudot is like ASCII, only older and more primitive - less bits, and a "shift" code to make the carriage hop into upper case.

One small nit... BAUDOT does not have upper and lower case. Uperr
only. The shift weas for non-alpha characters.

bill

All,

Here's a real world example of damaging undervoltage:

I once built a RTTY TU ( Terminal Unit ). The teletype had a "loop" consisting of a 120VDC power supply feeding a resistor and going to the selector magnets.

I used a high voltage transistor to switch the current on & off in time to the incoming baudot data. Baudot is like ASCII, only older and more primitive - less bits, and a "shift" code to make the carriage hop into upper case.

The transistor was safe as long as it was hard ON - zero voltage across it. OR hard OFF - zero current through it. Either one of these cases resulted in zero power dissipation.

IF OTOH you turned the transistor on just a little bit - say because of too low base voltage/current - that poor little transistor would let out its smoke with dispatch.

- Jerry KF6VB

CMOS input pins typically have on chip Schottky protection diodes to both the Vdd rail and to ground,
so any input signal above Vdd or below ground gets clipped by those diodes.
If the driver into that pin is limited to a few ma or if a series resistor is added to the signal trace,
the input buffers should be fine.

Here's the Nextion datasheet for a basic 5" unit:

It doesn't say much, but does say undervoltage can damage it.
This webpage hints that the backlight might be the issue:
? ??

As I said, I've never before run into an electronic component that warned of physical damage
due to undervoltage.? ?Very weird.

I am very curious if anybody knows more about this Nextion undervoltage issue,

Jerry, KE7ER

Indeed.
That's the power supply sequencing issue I mentioned in an earlier post.

Great to hear! Thanks, Dennis!


Reed

I'm still catching up on this thread.

Robert AG6LK wrote:
"I'm not sure why there could be damage to a display if the voltage dropped. On the enclosed paperwork, that came with the Nextion 5” display that I purchased, it said that there could be damage if the voltage dropped. They ?There was no explanation given why. They recommended a separate power supply."

That is not something I have ever seen in the documentation for an electronic component.
Could be something their lawyers thought was a good idea to put in there,
that way they can more easily insist the user goofed up when a part fries.

Or could be they actually see failures from too low of a voltage.
If so, that's a part I personally would avoid using.

Jerry, KE7ER

It may be possible to design a logic gate that works fine at 5v, and self destructs at 4v.
Such a product would not sell very many units.

A low power supply voltage can cause electronics to do unexpected things. but pretty much never
causes damage.? ?When bringing up a new board,? you are far more likely to cause damage by
bringing it to the target voltage suddenly instead of looking for trouble as the voltage is slowly increased.
Lots of things can kill a uBitx, but I wouldn't worry about operating at too low of a voltage.
Much more important to avoid over-voltage, watch for heat build up, and test with a good dummy load.

Reed is correct that writing to non-volatile memory with too low a power supply can cause corrupted data,
but if this happens we can simply reprogram the device.? A well designed device will lock out such writes
if the on chip voltage monitor shows the supply is too low.? A system that can't easily be fully reprogrammed
is a poorly designed system.?

It should be easier to save or record any critical EEPROM data on the uBitx.

The ATMega328P on the Nano? is spec'd to operate at a lower processor clock speed when operating
at 3.3v instead of 5.0v.? Operating the ATMega328P at 20mhz with a 3.3v clock can bring on
unexpected behavior, but would not damage the part.? As the gamers know, operating a high powered
processor clock speeds above the spec can cause the processor to overheat and do unexpected things,
but overheating is not an issue when operating at too low of a supply voltage.

I doubt there is much danger of damage to a CMOS output driver from a low power supply.
As Reed's Id vs Vds curves show, current through the device drops as either Vgs or Vds falls.
It can do unexpected things with a low supply, but it won't fry.
This applies to other push-pull drivers, such as the IRF510 final and the audio power amp.

I spent 40 years as a digital design engineer, sometimes bringing up boards with over a hundred IC's.
Sometimes just a few IC's, but with one or two being FPGA's with perhaps 1000 pins, a billion transistors,
and a half dozen different power supplies to sequence.? ?My preferred method of bringing up a new
design has been to power it from a bench supply with meters showing both voltage and current draw,
set the power supply's maximum current to a bit more than I expect the design to take, then very slowly
increase the voltage from zero volts with one hand while using the other hand to feel the board for
hot spots, checking any voltage regulators as they go into regulation.? ?I've seen plenty of smoke and
blown traces, but this has never been from a problem of feeding the board too low of a voltage.

Power supply sequencing is a whole other can of worms, something I was very careful to get right.
Occasionally I goofed and parts got warm, but never blew (they certainly could have blown).

Some extremely high powered logic parts (74ASxxx family parts, I'm looking at you) can overheat
and/or oscillate when an input signal is in the transition region between logic 1 and logic 0.? This is
why it is good practice to tie unused logic inputs to a solid logic 1 or 0 (typically to ground).
Many parts have some hysteresis designed into the input buffers, mostly avoiding this issue.

If the electronics is controlling a conveyor belt or an autonomous vehicle, this definitely must be?
designed in such a way that bad things don't happen when the electronics behaves in an
unexpected manner.? Fortunately, the uBitx does not fall into this category.

Often users here mention how the radio still seems to work with the power supply off, after
programming from a host computer over the USB port into the Nano.? In this case the 5v from
the USB cable is back-feeding through the LM7805 into the uBitx main board, which might be
seeing 4v or so.? ?Primary issue is you might burn something out on the Nano if the uBitx
main board draws too much current, I've added a 1n4007 diode in line between the 12v
line into the raduino and the LM7805 to prevent the USB port from powering the radio.

Jerry, KE7ER

It's already up to $52 plus shipping.

I have an untouched, unbuilt v3 still in the shipping box. Never opened, never touched by a soldering iron. What would be a fair price? Any interest here?

Clay NF7X

Anyone wanting the TSW Teensy 4.1 Raduino kit, they are still available.? We have located a source of 5351 clock/VFO chips and it turns out that Mouser electronics, at least, has over 700 Teensy 4.1's in stock so we are not dead in the water as first thought.

Details on the Raduino Clone kit that uses the Teensy 4.1 are on the TSW website, .

I have recently designed a chip test set for the Si5351a-b-gt and the Chinese version MS5351M and 100 percent test every 5351 chip we send out (already soldered on the PCB) for our T4.1 Raduino Clone kits.?

Take note, TSW sells these as a "you build it" kit only, for the uBITX V6,? they are NOT wired and tested units.? The kits come with the 5351 chip soldered in place, connections checked, and all other parts needed to build it LESS the Teensy 4.1 and the display. A NEXTION display WILL NOT work with this board as we designed it to use the original display from your V6 uBITX or an identical 2.8 inch ILI9341 Color TFT touch screen display from Amazon or other sources.

We have had several people not read the website info and think these T4.1 Raduino Clones were ready built and then got mad when they received kits.?

The pricing information on TSW's website is currently correct (kit is $35 plus shipping & handling).

Jim, W0EB
TSW Project Coordinator

Reed,
I want to thank you for the excellent job you did on the manual. It was easy to read and the steps for updating the firmware were easy to follow.
I ran into no hitches even though I had no previous experience with Arduino.

Over at /g/BITX20/topic/ubitx_v6_specifications/82557868 I saw some folks wondering how in the world something could be damaged by undervoltage, since as we all know, when things are turned off, they're at 0V. It's pretty obvious to most people that high voltage can cause all sorts of damage - sparks, heat, and the "magic smoke" - but the ways that undervoltage causes damage are a bit more subtle. In this rather lengthy post, I'll hopefully provide enough background to explain why undervoltage can be problematic, and give a couple scenarios where it could cause damage. While I do include a decent amount of detail, this is by no means meant to be a comprehensive guide.

TOO LONG; DIDN'T READ
Undervoltage can cause undefined behavior and partial-conductance, which can put your device in bad states and operating conditions, temporarily or permanently.

THE ANALOG NATURE OF DIGITAL LOGIC GATES
Digital logic assumes finite states, usually binary 0 or 1. In reality, all signals are actually analog approximation, usually with 0V for 0, and then some higher voltage for 1 - it could be 1.2V, 1.8V, 3.3V, 5V, etc., but let's assume in our system it's the Arduino 5V IO standard. With these two values in mind, consider an input voltage of 2.5V: is that a binary 0, or a binary 1? The answer, unsurprisingly, is "neither". However, that raises some serious questions. What should the system do if it encounters a 2.5V signal? The output needs to be a 0 or a 1, so we shouldn't output 2.5V, but picking 0V or 5V at random would mean our output data is random, which isn't what we want either. The only fool-proof solution is to "not do that" - don't ever send a signal that isn't a 0V or 5V. But if we're not allowed to send anything between 0V and 5V, then we'd never be able to change between 0V and 5V, since pesky physics says we can't instantaneously change voltage. Rather, we have to change over some (possibly very small but) non-zero amount of time. So if we want our system to be able to change (and thus actually do stuff), but we also don't want any voltage except 0V or 5V, then we need a way to ignore all the middle voltages, and only look at the 0V and 5V signal states. That's where propagation delay and clocks come in. The clock on a digital circuit provides a way to only look at the input voltages at certain times. As long as the time it takes to switch voltages from 0V to 5V and 5V to 0V are shorter than the clock period, we know that when the clock signal comes, our inputs will all look like either 0V or 5V, just like we wanted! Great!

Let's suppose the input signal to our system that is only 4.9V, not 5V. This could be due to a manufacturing defect, or some resistive loss on the input, but regardless, 4.9V looks a lot like 5V, so we probably want to interpret it as a binary 1, and output a 5V signal. But we said before that 2.5V is undecidable, so there's got to be some threshold at which we can confidently call a signal binary 1, and another threshold we can confidently call a signal binary 0. We call the highest voltage at which an input will definitely be considered a binary 0 "Voltage Input Low", often shortened to V_IL. We call the lowest voltage at which an input will definitely be considered a binary 1 "Voltage Input High", often shortened to V_IH. If we consider an inverter, the graph of inputs vs outputs usually looks something like this, assuming a fixed nominal system voltage:

You'll note that the V_IL and V_IH are somewhat conservative. This is intentional. We expect some process manufacturing variation, so we define V_IL and V_IH not so that they're mathematically the most pleasing (e.g. <2.5 is a 0, >2.5 is a 1), but rather so that in the worst case - if all our expected manufacturing variations all push the curve in the wrong direction - inputs at V_IH and V_IL will still produce the correct output signals. Cool! Our system now works nominally with 0V and 5V signals, but also tolerates some amount of "real life" variation.

UNDERCLOCKING
Next suppose you provide your system with 3.3V instead of 5V, not as the input, but as the supply voltage. Now none of the signals are 5V, so are they all binary 0's? Well obviously not - we can define 3.3V as the new value for binary 1, and we're happy, right? Not quite. Digital logic is actually a bunch of analog transistors running to saturation to produce those nice high 5V 1's and low 0V 0's. If we assume they are MOSFETs, then our logic gate's input voltage allows current to flow, which charges up the gate capacitance of the next logic gate. No problems so far, but unfortunately (in this case), transistors operate differently depending on their gate voltages and the difference between their drain and source voltages. You've probably seen a graph of gate voltage vs current that will pass through a MOSFET like this:

Why do we care? Because what it tells us is that if our system voltage is lower, both V_GS and V_DS will be lower, which per the graph means that our drive current will also be lower. The drive current is what determines the propagation delay between receiving a new input (V_GS) and achieving our desired output (now 0V or 3.3V), since we need to charge the next logic piece's gate capacitance. If we have less current, it takes longer to charge the next gate, so our propagation delay increases. If our propagation delay increases too much, we may take longer to achieve our desired output than it takes for the next clock signal to come! Note that there's an easy fix for this. If we increase our clock's period, decreasing it's frequency (known as underclocking), then we can give ourselves more time for the signal to propagate, and thus make sure we reach our desired output before the next clock signal arrives. Crisis averted! But do we actually have control over our clock speed? In a lot of cases, we do at design time, but not while operating. For instance, if we picked a 16MHz clock suitable for 5V, but then only provided 3.3V, then 16MHz may be faster than the system can actually propagate the full signal swings, so we may be stuck getting bad values at 3.3V.

WHAT'S THE WORST THAT COULD HAPPEN?
We've discussed some issues with signals being in mid-way points, and saw that it can make it difficult to decide on a "correct" output choice, but haven't examined what sorts of problems it can cause. For some applications, like in medical equipment or a guided missile, it's easy to understand that a single miscalculation could literally be life-and-death. Okay, fine. But we're dealing with hobby radio stuff, so what's the harm in a wrong bit from time to time? Just power cycle the radio and we're back to business, right? Often times, in practice, that's probably right. However, consider what it means to run a program. The processor is constantly changing many bits at once, and in most consumer and hobby grade devices, the processor assumes that every operation it does is done correctly every time. If a bit that is supposed to be a 1 isn't quite high enough (less than V_IH), or a 0 isn't quite low enough (more than V_IL), then what happens next is largely up to chance.

For instance, if the program counter reads a 1 where it was supposed to be a 0, then you've suddenly ended up at a random location in your code, and will start executing who knows what instructions, which will re-interpret your stack data in any sort of manner. Often times this will lead to invalid instructions being attempted and crash, but it could also end up being more subtle, where the program still runs, but is now operating on the wrong data. A mis-interpreted bit in a register could cause the program to activate some undesired behavior, like turning the transmitter circuit on when it shouldn't be, or cause us to save the wrong configuration data. Since we don't know which bits are more or less likely to fail first due to lower voltage, it's impossible to say exactly what failure mode we'd see.

In a lot of scenarios, turning the system fully off, then re-powering with sufficient voltage will recover. However, for systems with non-volatile memory (e.g. flash), an undervoltage system voltage can corrupt or destroy data, rendering the system inoperable or "bricked". Similar to our logic gates above, non-volatile memory requires certain electrical parameters in order to store values that are "definitely 0" and "definitely 1". If we apply insufficient voltages when writing to these memories, we can end up with bits stored as in-between states, that aren't clearly readable as 0 or 1. When reading back properly stored data, insufficient voltage can corrupt our read process, returning incorrect bits. If this memory happens to be our program data, then incorrect bits could make it impossible for us to successfully run our program or boot. In particular, if this program data was written by the factory, or happens to be one-time-programmable, and we don't have the ability to reprogram the memory from an external programmer, we may now have "bricked" our system for good.

Finally, to see some real potential for damage, let's consider a typical CMOS inverter gate:

When V_in is 0V or 5V, one of the FETs is fully on, and the other is fully off, so current can only flow to or from V_out. However, if our system voltage is too low, we can get into a state where both FETs are consistently partially-on, meaning there is a direct path from the system voltage, through the FETs, to ground. Depending on the nature of the FETs, the current flow could be enough to fry them, or the resistors or wires they're connected to. Even if the FETs themselves survive, with enough gates in these unstable states, our system could end up oscillating wildly from small system voltage fluctuations, and/or draw significantly more current than it would during normal voltage operation, potentially damaging other components, like the power supply, or even indirectly damaging adjacent parts due to excessive heat generation. Note that this particular problem is not specific to logic gates in a processor, but also applies to similarly-configured push-pull transistor setups, like H-bridges.

TURNING OFF AND ON
To power a device on or off, there must be some time during which the system voltage is greater than zero, but not yet in the "safe" area, so why don't digital devices corrupt, fail, or self-destruct constantly? There's no one single answer, because different devices have different solutions to this problem. Some devices have built-in circuits specifically designed to detect the supply voltage, and only enable themselves once the voltages are high enough to be safe. An example of this is the brown out detection system in the Arduino. Many devices have requirements for how long their supply voltages are allowed to take to transition from 0V to the target (e.g. 5V). Just like the propagation delay with periodic clocks, if the supply voltage comes up fast enough, all signals can be "locked in" to good states before any uncertain behavior regions have a chance to corrupt bits, or significant current can pass through the partially-on FETs. A related solution is to not provide the clock signal until the supply voltage has been up for a certain amount of time. This ensures that no logic gates are required to read input signals until those input signals have had time to stabilize.

For powering down, similar rules apply. The device might require voltage to drop from the nominal system voltage to 0V within a certain amount of time, or to stop the clock input prior to removing power. It may also require that potentially unsafe operations, like writing to non-volatile memory, be stopped some amount of time before removing power. In more complicated systems, we may need to remove power first from the "dangerous" parts, like the high voltage from a motor driver for an antenna rotator, or disabling writes to non-volatile memory, before removing power from the respective controller unit. In this way, while there may be a few mis-interpreted bits as the system powers down, they won't be able to cause dangerous or long-lasting behavior.

Hi all,

Thank you for all for your information and comments.

Bill,

I'm not sure why there could be damage to a display if the voltage dropped. On the enclosed paperwork, that came with the Nextion 5” display that I purchased, it said that there could be damage if the voltage dropped. They ?There was no explanation given why. They recommended a separate power supply.

Evan,?

Do you think that a Buck converter module would be a good to supply 5v for the Nextion. I'm not quite sure how to set up a power supply using the 7805 voltage regulator. That's why I thought the Buck converter would make a good choice, it's prebuilt. What do you or anyone else think? Thank you in advance,?

Bought a very nice chassis and ordered a ver 6 board. Looking to buy a 5" Nextion display....what is the best model number? I see a few choices on amazon.
Thank you - Mike