Hi James
Add on
If you are having trouble with getting LMC6482 you could try reversing the positions of the 3k3 and 10k divider resistors and using the LM393. That will get the pin 2 and 3 input down below the 393 upper input threshold. You could also increase the 3k3 to 4k7 which will put the inputs centred around 1V. That might work with the 393. If I get a chance will try later.
Cheers Bob
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Hi James
I finally had time to lay around with swapping the 3k3 and 10k resistor positions with an LM393.
This certainly moved the switching range down to within the 393 input limits but the hystereses didn’t like it too much. The descending switch point became far too low. I don’t think the hystereses circuit thought too much of being too close to ground (3k3) so I sort of discarded that idea.
I returned the ground side of the dividers to 10k and increased the top resistor value to get the reference to somewhere near 1V and keep the 393 input below the max (1V8) with max 4V2 at VSYS.
I have arrived at the following.
Original circuit with the following changes.
3k3Ω changes to 24kΩ
10kΩ remains as the ground side of the dividers.
100kΩ changes to 470k.
10kΩ resistor across LED to remove any effect on hystereses.
I have used a 3V2 lithium as 3V3
Actual measured results using the same multimeter throughout so any measurement errors will be the same way. Multicomp Pro MP730624.
3V3 measured 3V35
Reference Pin2 measured 0.989
Switches at VSYS voltage:
VSYS reducing 3V07
VSYS increasing 3V46
Switching without hystereses approx 3V35 both ways which one would expect.
The ICs I have are LM393-N and I have had for some time so a later build might work down to the quoted 2V . Probably is OK for a straight out comparator but when you start fiddling like adding hystereses it seems to be a bit fussy and like something like 5V to settle down.
While this experiment seems OK for your type of application at VCC 3V3 I would be much happier if I could give it 5V as at 3V3 it seems a bit more fussy about resistor values.
There are obviously other comparators and Rail to Rail Op Amps available if one searched but SMD components are fast becoming the norm and some types no longer manufacture through hole versions which are still the go to for breadboard use.
Jim I don’t think I can offer any more. My preference would be the LMC6482 as it does not suffer the same input restriction, it is actually VCC + 0.3V. Nothing above that though as it will stress the input protection diodes without a current limiting series resistor at the input. But that is not hard to arrange if the need arises.
Cheers and I hope I have been of assistance. Bob
PS I knew there was a reason I stay away from 3V3 unless I have to go that way.
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Hi Bob,
Thanks for what you have done and posting here, I will add to the documentation.
I haven’t tried a LMC6482 yet, other things have got in the way.
When the LM393 was designed 5V was the lower limit in most things. Using it at 3V3 is the edge of its designed operating range. Probably they came out with a low voltage version because of the shift to lower voltages for modern stuff and in a SMD footprint to fit the smaller size of devices.
Anyway, this has been an interesting experience and your help is much appreciated.
Thanks
Jim
Hi James
I think probably longer than that. It was around when +/- 12V RS232 was considered to be the be all to end all
I did not notice any through hole packages in that low voltage version you linked earlier.
From one of your earlier posts
So you see analog has it’s fun times also. In spades sometimes but I have found over the years that both disciplines very often overlap.
A modern example mostly not appreciated is the use of high speed data when long (ish) PCB tracks have to be used they are sometimes several wavelengths (analog jargon) long and are in fact transmission lines with a characteristic impedance. If not properly terminated echos and reflections can and will play merry hell with the data stream.
Anyway you are very welcome to any help I have been.
Cheers Bob
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Hi James
Just had a closer look at the lo voltage, ie; LMV393. It appears that the input voltage can range from 0V to VCC which removes the upper input voltage limit. It will also sink 23mA, up from the 16mA of the LM393.
I looked at the ON Semi data sheet and there is no mention of a through hole package.
Next point is where do you get it. Mouser, DigiKey and element 14 have them (surface mount package) but in all cases postage might be a killer. If you live anywhere Chester Hill, NSW, Element 14 have a sales counter (or used to)
Cheers Bob
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