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Unnecessarily high QCX Brown-out reset voltage? #qcx

Torbjorn Skauli
 

Hans, here is a narrow-interest request that you can read when you have time:

In my compact 3D-printed QCX cabinet, I would like to switch off the GPS while keeping the processor running. This is very useful because it allows to get WSPR locator/time/frequency by moving the QCX temporarily to a location with good GPS reception, perhaps with practice mode on, and then to turn off only GPS and move the transceiver into the shack or wherever it needs to be, where lack of GPS reception may prevent WSPR from working. The way I have designed the power control, this would require a make-before-break DPTT switch, which appears difficult to find in a suitable size.

An alternative solution would be to put a millifarad or two across the 5V to keep the processor alive during the switch changeover. However the processor resets after only a small voltage drop, therefore I need more capacitance than I can fit in the tight space I have. As I understand, this indicates that the BODLEVEL brown-out reset fuse in the processor is set for the highest voltage: My QCX resets if the 5V line drops below about 4.3V, consistent with the highest reset voltage setting (BODLEVEL fuses set at 100). This is fair for a processor that runs off a 5V regulator, of course. On the other hand, I suppose it would not hurt much to reduce it?

So Hans, if you can find the time to create a QCX firmware update with a lower brown-out reset voltage then I would be happy to buy a new processor. (And as a bonus I would be happy to print you the parts for a cabinet, if you wish :-)

There may be alternative ways to solve the problem, of course. I am interested if anyone have suggestions that can work within the format of the compact cabinet.

73 de Torbjorn, LA4ZCA

Arv Evans
 

Torbjorn

A single Li-ion cell could provide 3.2 to 4.0 volts (depends on charge state) for powering the GPS receiver
part.  Very small 1S Li-ion charger boards are available from Ebay suppliers and could be used to keep the
Li-ion cell charged during normal use. 


Arv
_._


On Sun, Jun 30, 2019 at 2:46 PM Torbjorn Skauli <tskauli@...> wrote:
Hans, here is a narrow-interest request that you can read when you have time:

In my compact 3D-printed QCX cabinet, I would like to switch off the GPS while keeping the processor running. This is very useful because it allows to get WSPR locator/time/frequency by moving the QCX temporarily to a location with good GPS reception, perhaps with practice mode on, and then to turn off only GPS and move the transceiver into the shack or wherever it needs to be, where lack of GPS reception may prevent WSPR from working. The way I have designed the power control, this would require a make-before-break DPTT switch, which appears difficult to find in a suitable size.

An alternative solution would be to put a millifarad or two across the 5V to keep the processor alive during the switch changeover. However the processor resets after only a small voltage drop, therefore I need more capacitance than I can fit in the tight space I have. As I understand, this indicates that the BODLEVEL brown-out reset fuse in the processor is set for the highest voltage: My QCX resets if the 5V line drops below about 4.3V, consistent with the highest reset voltage setting (BODLEVEL fuses set at 100). This is fair for a processor that runs off a 5V regulator, of course. On the other hand, I suppose it would not hurt much to reduce it?

So Hans, if you can find the time to create a QCX firmware update with a lower brown-out reset voltage then I would be happy to buy a new processor. (And as a bonus I would be happy to print you the parts for a cabinet, if you wish :-)

There may be alternative ways to solve the problem, of course. I am interested if anyone have suggestions that can work within the format of the compact cabinet.

73 de Torbjorn, LA4ZCA

Hans Summers
 

Hi Torbjorn

I'd be happy to program a chip for you with a lower brownout fuse setting. Available values are 4.3V, 2.7V, 1.8V. If you order a chip from the shop please make a note on the order, or send me an email, so I can make sure it is programmed correctly with the fuse values for lower brownout. 

I'm not completely convinced it solves your problem but it may. Other issues could arise for example the LCD module could have some voltage threshold below which it corrupts whats on the display. Anyway you can give it a try!

73 Hans G0UPL

On Sun, Jun 30, 2019 at 11:46 PM Torbjorn Skauli <tskauli@...> wrote:
Hans, here is a narrow-interest request that you can read when you have time:

In my compact 3D-printed QCX cabinet, I would like to switch off the GPS while keeping the processor running. This is very useful because it allows to get WSPR locator/time/frequency by moving the QCX temporarily to a location with good GPS reception, perhaps with practice mode on, and then to turn off only GPS and move the transceiver into the shack or wherever it needs to be, where lack of GPS reception may prevent WSPR from working. The way I have designed the power control, this would require a make-before-break DPTT switch, which appears difficult to find in a suitable size.

An alternative solution would be to put a millifarad or two across the 5V to keep the processor alive during the switch changeover. However the processor resets after only a small voltage drop, therefore I need more capacitance than I can fit in the tight space I have. As I understand, this indicates that the BODLEVEL brown-out reset fuse in the processor is set for the highest voltage: My QCX resets if the 5V line drops below about 4.3V, consistent with the highest reset voltage setting (BODLEVEL fuses set at 100). This is fair for a processor that runs off a 5V regulator, of course. On the other hand, I suppose it would not hurt much to reduce it?

So Hans, if you can find the time to create a QCX firmware update with a lower brown-out reset voltage then I would be happy to buy a new processor. (And as a bonus I would be happy to print you the parts for a cabinet, if you wish :-)

There may be alternative ways to solve the problem, of course. I am interested if anyone have suggestions that can work within the format of the compact cabinet.

73 de Torbjorn, LA4ZCA

DL8LRZ
 

Hi Torbjorn
When reducing the threshold voltage of the Brown-Out-Dedektor, it should be noted that the safety of the EEPROM depends on it (see Datasheet ATMEGA328P). No specific voltage value is mentioned in the datasheet, but referenced to the dependence on the clock frequency.

Example: The Brown Out detector of the ATMEGA of my QCX was (for whatever reason) switched off in its original state. Between 10 to 40 on / off switching operations, the error "select band" (re-entry of all user values required) or "USE ORIGINAL CHIP" (reprogramming EEPROM required)
After properly programming the fuse of the Brown-Out Dedector, these errors were eliminated.
73 Reiner DL8LRZ

Torbjorn Skauli
 

Thanks a lot, Hans. I have just placed an order with a comment to get the lowest brownout voltage.

I will report back here what I find out.

73 de Torbjorn, LA4ZCA

Torbjorn Skauli
 

Reiner,

As far as I can see, there should be no EEPROM write activity initiated by the processor, except just after a WSPR transmission where the GPS is read. By avoiding a switchover or switch-off at that particular time, both EEPROM and processor state should be preserved. The ATMEGA datasheet specifies that devices are tested down to the lowest BOD level. We will see what mileage I get.

73 de Torbjörn

Hans Summers
 

Ok Torbjorn

In will sort it all out but it will have to wait until I'm home on 17th July.

73 Hans G0UPL 


On Mon, Jul 1, 2019, 22:41 Torbjorn Skauli <tskauli@...> wrote:
Thanks a lot, Hans. I have just placed an order with a comment to get the lowest brownout voltage.

I will report back here what I find out.

73 de Torbjorn, LA4ZCA

Torbjorn Skauli
 

No problem. And no hurry. Have a nice summer, hopefully including some vacation ;-)

Torbjorn

Torbjorn Skauli
 

I finally installed the new chip with lower brown-out voltage threshold today. At the same time I installed a 2200 uF/6.4V capacitor across the output of the 5 volt regulator into my 3D printed QCX cabinet (filling the last remaining volume in there: https://groups.io/g/QRPLabs/topic/31672996). This clearly has the desired effect: I can now rotate the break-before-make power switch to turn the GPS off while keeping the processor alive. This enables the following use case:
- Set up the QCX in a convenient indoor location with no GPS coverage
- Enable practice mode and WSPR beacon
- Disconnect from antenna temporarily and move the QCX in a location with GPS coverage
- Leave it on with GPS enabled until GPS PPS is flashing AND WSPR completes a cycle, so that time, frequency and locator are set automatically
- Turn the power switch one click to disable GPS
- Bring the QCX back indoors and connect the antenna
- Disable practice mode, and let WSPR run

It may look complicated, but is actually easy as long as the QCX is a complete unit with battery. This will surely help to get WSPR running correctly in new places without having to look up the right locator and get the clock set right manually. Not least, this is useful when showing off the magic of WSPR to other people, for example at exhibits of ham radio.

Thanks again, Hans.

  Torbjorn, LA4ZCA