Low voltage operation
- Thread starter TinkerJim
- Start date
The 08M runs quite happily on supplies from below 3V to ~5½ Volts. Although you won't "damage it", programs could freeze if the supply falls too low. Even then a BOD (Brown Out Disable) command can assist. Best you specify your application- I'd be more concerned with solar outputs that may surge above 5½ V.
I've run an 08M down to 1.1V before it died. It wasn't doing any heavy lifting though, just sleeping for ten seconds before waking up briefly to beep a piezo and go back to sleep again. I used the 'DisableBOD' command to get it down to that voltage without locking up though. I also ran it down at 31KHz, normal speeds would probably make it die sooner than that.
Pauldesign
Senior Member
Hey TinkerJim
Welcome to the PICAXE forum.
Bear in mind, low voltage below specs may also cause program codes corruptions and unstable or unreliable operation of the 08M or any embedded microcontroller.
Welcome to the PICAXE forum.
Bear in mind, low voltage below specs may also cause program codes corruptions and unstable or unreliable operation of the 08M or any embedded microcontroller.
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fernando_g
Senior Member
If the average current consumption is low, and the voltage will never be above 5.5 volts, a supercapacitor may be the answer.
TinkerJim's post implies that he isn't using it at night, as his low voltage concerns are for both morning and evening.
Thus the questions appear to be of the following nature, "what happens when the picaxe is being powered by lower voltages than it is designed to operate on?
Does it damage the chip?
Does it corrupt the program so it will not restart in the morning?
Will it start up properly from a very slow rise in input voltage, or might it lock up?
Thus the questions appear to be of the following nature, "what happens when the picaxe is being powered by lower voltages than it is designed to operate on?
Does it damage the chip?
Does it corrupt the program so it will not restart in the morning?
Will it start up properly from a very slow rise in input voltage, or might it lock up?
I thought it had been pretty well covered by Stan in Post2.
For a fuller answer some clarification is needed.
We maybe talking about POR as well as BOD/BOR....?
The whole point of designing a 'thing' is that it should behave predicatably.
A really slow Power Up may defeat the POR, for example.
I feel that disabling BOR in a battery powered circuit maybe asking for trouble.
So, are we talking about a solar-only-powered PICAXE?
Where, at the evening and morning (dusk and dawn) the power is a bit iffy and during the darkness it is definitely off?
This won't 'hurt' the micro but it's not a good way to run things.
Switching to battery + micropower mode , or, a micropower twilight switch is really the way to go. A small lithium could provide years of backup if designed correctly. A micropower op-amp +ref+switchfet could provide an easy twilight switch.
The bottom line is that you want CLEAN operation, not dithery. Dithery = unpredicatable.
A schematic would really help. Get into the habit of providing schematics or background.
PS. here's a little bed time reading...
http://ww1.microchip.com/downloads/en/AppNotes/00522e.pdf
For a fuller answer some clarification is needed.
We maybe talking about POR as well as BOD/BOR....?
The whole point of designing a 'thing' is that it should behave predicatably.
A really slow Power Up may defeat the POR, for example.
I feel that disabling BOR in a battery powered circuit maybe asking for trouble.
So, are we talking about a solar-only-powered PICAXE?
Where, at the evening and morning (dusk and dawn) the power is a bit iffy and during the darkness it is definitely off?
This won't 'hurt' the micro but it's not a good way to run things.
Switching to battery + micropower mode , or, a micropower twilight switch is really the way to go. A small lithium could provide years of backup if designed correctly. A micropower op-amp +ref+switchfet could provide an easy twilight switch.
The bottom line is that you want CLEAN operation, not dithery. Dithery = unpredicatable.
A schematic would really help. Get into the habit of providing schematics or background.
PS. here's a little bed time reading...
http://ww1.microchip.com/downloads/en/AppNotes/00522e.pdf
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TinkerJim
Member
More details on low voltage question.
Wow...thanks for all the replies! I am working on a solar only powered model car. The solar cells charge up a super cap, and when the voltage is 4V, the 08M turns on the motor via a transistor and it stays on until voltage drops to about 3.5V. Then the cap charges up again.
I breadboarded a circuit that works just perfect using a MAX 6018 as a voltage ref. (many thanks to NXTreme and kranenburg for recent posts on this). Now an S808 voltage detector driving a ZVN110A would be a proper way to power up the 08M in this circuit at around 3 or 3.3V. But I was wondering if the power-up circuit could be omitted without harm.
I had made a test circuit in the form of a low duty cycle flasher. A solar cell charges up a 1F cap and that powers the 08M with an LED off pin 2.
Here is the simple program:
Main:
High 2
Pause 20
Low 2
Disablebod
Sleep 2
Enablebod
GotoMain
In the morning, when the cap voltage reaches about 2.1V, the flasher starts working just fine. The blinking goes on into the night until charge gets too low. It's been working day to day fine this way for maybe a week.
That's the background to my original query.
Thanks again for all the useful comments!
Wow...thanks for all the replies! I am working on a solar only powered model car. The solar cells charge up a super cap, and when the voltage is 4V, the 08M turns on the motor via a transistor and it stays on until voltage drops to about 3.5V. Then the cap charges up again.
I breadboarded a circuit that works just perfect using a MAX 6018 as a voltage ref. (many thanks to NXTreme and kranenburg for recent posts on this). Now an S808 voltage detector driving a ZVN110A would be a proper way to power up the 08M in this circuit at around 3 or 3.3V. But I was wondering if the power-up circuit could be omitted without harm.
I had made a test circuit in the form of a low duty cycle flasher. A solar cell charges up a 1F cap and that powers the 08M with an LED off pin 2.
Here is the simple program:
Main:
High 2
Pause 20
Low 2
Disablebod
Sleep 2
Enablebod
GotoMain
In the morning, when the cap voltage reaches about 2.1V, the flasher starts working just fine. The blinking goes on into the night until charge gets too low. It's been working day to day fine this way for maybe a week.
That's the background to my original query.
Thanks again for all the useful comments!
It seems to me the point of designing a thing is that it should behave predictably when one wants it to behave predictably.
If there are times when keeping things predictable is not necessary, then a good design might save time and money by making things simpler, as long as no harm is done when the circuit behavior is unpredictable.
That appeared to be the nature of the question posed to us here.
Like Dippy, and most other good technical people I know, I personally like my electronic devices to operate reliably under all circumstances. (In fact, I'm well known and laughed at for heavily over-building just about all of my projects. Hi-Fi amp power supplies with 200,000 uF caps? Just about right. What can I say?)
But sometimes that's just not necessary or desired, and depending on the nature of the project, it may be entirely detrimental.
Good engineering practice boils down to understanding the desired result, and getting it simply, reliably and inexpensively, while ensuring that safety and other peripheral requirements have been attended to as well.
As with many of the other questions posed in the forum, our lack of knowledge of the specific intent of the questioner, the amount and type of their expertise and the exact details of the project, lend to our initially providing a variety of different answers, all appropriate and correct from different points of view and with different basic assumptions, none of which may match those of the questioner.
So we stumble along as we work our way through these threads, learning more and more about the exact nature of each project and its individual requirements, providing better (more appropriate for the user's goals) advice with each post.
I think we do a pretty good job of it by the time all is said and done.
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