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<set_>
Oh and A-Okay...
<set_>
I am grounded, physically. So, there is still something I am missing. The board knows its GPIOs work (due to bbb people) and me testing it but...
<set_>
1) Either the logic is off (this and a number of other things). 2) The circuit is off. 3) Both...
<set_>
So, would using voltage divider circuit per GPIO be unheard of during Op-Amp testing for drivers?
<set_>
I got the GPIO pins that are available now in the source and still, just excited motors. No movement...
<set_>
Anyway, if one person gets time and can shed light here, yay! If not, okay too.
<set_>
tomllib and python3.11 and pyproject.toml easy ideas...
<set_>
It is like all three are working in cahoots to not be friendly to one another.
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<ds2>
what are you trying to do?
<ds2>
trying to understand why you are using voltage dividers on the GPIO
<ds2>
set_
<set_>
Right.
<set_>
for the LM358N OP-AMP.
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<set_>
ds2: If you understand the 3.3v to 1.65v for accessing the LM358N, I would guess you understand inverting and non-inverting signals too which is what I am dealing with currently.
<set_>
And I think I need to not use the enable signal on the driver via a second LM358N from GPIO on the beagley-Ai or BBB.
<set_>
excited yes but it still does not move.
<set_>
brb...I think I may be on to something.
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<set_>
I figured I needed to add some voltage to the non or inverting pins of the LM358N and then bring it to gnd.
<set_>
Then, the 3.3v bypasses the gnd and goes to the driver since my 1.65v is at GND.
<set_>
at least, this is what I thought would work...
<set_>
it does not.
<set_>
man, Debian and Python3 are complicated. It is like you need a build of Python3 on a home computer built to suit the needs of specific SBCs like the BBB and beagley-ai.
<set_>
ds2: I am trying to drive some inverting and non-inverting pins from the BBB/BeagleY-Ai to a driver for stepper movement.
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<ds2>
so you are trying to level shift from BBB (3.3V CMOS) to something else? like 5V TTL?
<ds2>
the LM358 is a linear op-amp so not sure what you are expecting from that
<ds2>
I don't know how fast you need this to go but there are simplier ways
<Shadyman>
didn't catch the first part of the conversation, but easiest would probably be the TXB or TXS0102 /0104 /0108. Cheapest would probably be a FET ala sparkfun or adafruit level conversion board, you can look at their schematics. really depends what levels you're trying to reach
zjason` is now known as zjason
<set_>
Oh.
<set_>
The only, I think now, 5v translation that needs to be made is on the "OPTO" line which is some PWR line on the DM332T driver.
<set_>
The other two lines can be controlled via 3.3v CMOS GPIO lines.
<set_>
There is an enable pin but it stays enabled from the get go... I may incorporate it or not. I have not made up my mind so far.
<ds2>
if the other side is 5V, use a bipolar transistor
<ds2>
2n2222, 2n3904, etc.... open collector and call it a day
<ds2>
those are easy to get and don't have gotcha parameters like with FET.... the TX* chips are nice but a bit overkill
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<ds2>
since you are going for 3.3 -> 5V, you cannot use a resistor network... HOWEVER since you are driving a device (vs reading from it) - check the datasheet
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<set_>
i did and I will keep reading it.
<ds2>
Look at the Vinh min parameter.... and check the TI335x Vouh min parameter... if the 335x's Vouthi min is higher or equal to the Vinhi min on the otherside, you are good...just make sure it is an input only pin on the device not a bidirectional pin
<set_>
Right.
<set_>
Thank you.
<ds2>
IIRC, if the other side is true TTL input, the 3.3V CMOS can drive directly
<set_>
I just do not want EMI or other drifts.
<set_>
Hence the network(s) of inversion.
<ds2>
though technically, you do loose noise margin for the low signals as CMOS should be 1/3 of 3.3V whereas TTL is a little bit lower
<ds2>
If it is really that critical, I'd just use an open collector bipolar and call it done
<set_>
I have 3.3v on inverting and 1.65v on non-inverting signals of the Driver.
<set_>
Right.
<ds2>
quick and cheap
<set_>
That is my drift.
<ds2>
don't use analog op-amps for this
<set_>
I get it. Easy-peasy.
<ds2>
between input offset and sometimes no rail to rail driving, you will be in a world hurt reading the fine print
<set_>
I saw one link listed from a ti e2e chat...
<ds2>
if you must, use a comparator like the old LM339 or a LM311
<set_>
2n7002
<ds2>
the reasons against fets (yes, you save 1 resistor but...) is you need to check parameters like Vth
<set_>
I thought of that idea with the square wave generator of the comparator types.
<set_>
I made it this difficult because of the parts I currently have in stock.
* set_
says being broke now is a lot of "fun!"
<ds2>
that is not guarantee to work per the specs
<set_>
Oh.
<set_>
So, jumping 1.65v into the opposing pin is neglect or not satisfactory with this specific op-amp?
<ds2>
going by memory (confirm in datasheet) if the 335x is 3.3V CMOS, high min is 2.2V.... Vth can be as high as 2.5V so the tranistor may not turn on
<set_>
Aw.
<ds2>
you want the opamp option? let me look... I was referring to the 2n7002
<set_>
Well...
<ds2>
what's the op-amp pn again?
<set_>
I do not currently have the 2n7002.
<set_>
LM358N
<set_>
ti chip.
<ds2>
how is it wired?
<ds2>
how is it powered?
<set_>
Let me double check.
<set_>
3.3v
<set_>
I have 3.3v powering two op-amps (LM358N) chips.
<set_>
I may have some BJTs.
<ds2>
from a quick read, I don't see anything about unipolar power supply nor do I see anything about rail to rail operation
<set_>
Hmm. So, what are you saying about the LM358N now?
<ds2>
nix that.... the N version did say it can run from unipolar down to 3V
<set_>
I need separate PWR supplies per chip?
<set_>
Right. I am with you...I can power the chip via CMOS.
<ds2>
okay, it won't work - max output is V+-1.5V
<ds2>
so you will not get a valid logic output even if you did wire it up as a comparator
<set_>
With the 2n7002, I can do it supposedly but I do not have that in stock.
<ds2>
that is not guaranteed to work per the datasheet
<set_>
Okay.
<ds2>
unless the 335x can guarantee a high is no lower then 2.5V.... AFAIK, it only guarantee it to 2.2V
<set_>
Hmm.
<ds2>
just get yourself a bag of 2N2222's
<set_>
I must have...ha. Okay.
<set_>
2n2222 got it.
<set_>
I will...
<ds2>
I have the circuits in my book... let me see if I can find the diagrams locally
<set_>
Okay. have at it...
<set_>
Nothing I am doing now works. So, any insight is good sight.
<set_>
I see the 2n2222 is not a ti part.
<set_>
Should this matter?
<ds2>
no... it is so generic
<set_>
Oh.
<set_>
I see OnSemi make them...
<ds2>
2N3904 also works
<ds2>
MMBT3904 or MMBT2222
<ds2>
I keep pile of them around.... if you have any small signal NPN transistors around, it'll probally work... .esp if it is a SOT-23 or a TO-92 case
<set_>
I got those!
<ds2>
TO-220 may even work but I'd waste time with a TO-3 styled one... power transistors tend to have a lower beta (gain)
<set_>
TO-92s.
<ds2>
TO-92 is just a package name
<ds2>
just make sure it is a NPN transistor
<set_>
I will need to rummage through some stuff but yep, I know they are somewhere.
<set_>
It is.
<set_>
NPN type.
<ds2>
if you are paranoid and have a DMM with a transistor check function, check the beta... >150 should be good
<set_>
Back to the old drawing board.
<set_>
I will check...
<set_>
I do not think my ohm function currently works.
<ds2>
Look at the section entitled "Open Collector Circuit".... the base resistor can be about 470ohm - 1K
<ds2>
just another domain
<set_>
I am paranoid. i cannot do it.
<set_>
I am sorry.
<ds2>
just read the P/N stamped on the transistor and look it up
<ds2>
I just mentioned the meter method in case you had a pile of old dead boards that you are desoldering parts from :D
<set_>
ha.
<set_>
Aw...
<ds2>
those parts are not always labeled
<set_>
Good idea.
<set_>
I have some new parts somewhere, i.e. hence rummage.
<set_>
I broke down about four years ago to get the bjt types.
<set_>
NPN.
<set_>
Now, did I need them at the time and got rerouted? Yes.
<set_>
Will it take too much time to research the whereabouts? yes.
<set_>
Locating them in swift timings...priceless.
<set_>
off to test my org. skills.
<set_>
brb
<ds2>
go SMT... they are easier to organize...esp if you get them in reels :D
<set_>
Boo-ya!
<set_>
BC547
<ds2>
that'll work just fine...just make sure you have 2 resistors...about 470-1K on the base .... the collector resistor depends on how fast you need it to go...
<set_>
You got me scared...
<set_>
Are you sure?
<ds2>
how so?
<set_>
The LM358N has been trying...right.
<set_>
So, trying some new hardware may not go right.
<ds2>
your call...
<set_>
So, the base goes to gnd right?
<ds2>
yeah
<set_>
Okay...
<set_>
I will get out the oscilloscope to test too.
<set_>
I do not need super powers yet.
<ds2>
no need...just learn on simple things like DMM's.... scopes are such a luxury item
<set_>
Luxury!
<set_>
Like an old, Lincoln TOwn car!
<ds2>
:D
<set_>
Man, I miss Licoln.
<set_>
They ended up odd...
<ds2>
anyways, enjoy... just look up open collector circuits.. it is an old concept so there are plenty of stuff on it
<set_>
I got one.
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<set_>
ds2: I got one of these too -> L293x Quadruple Half-H Drivers
<set_>
I was thinking I could map the output of the LM358N to the L293D.
<set_>
It takes TTL logic but...
<set_>
I can translate the output of the LM358N to be about 4.5v.
<ds2>
donno if it will even for that
<ds2>
if you power it from 5V, the high is taken care of but will it go down to 0? or is it min 1.5V out?
<set_>
Oh.
<set_>
Hmm.
<set_>
Probably, should be 4.5v to 3.3v.
<ds2>
TTL needs it to go down below 0.4V
<set_>
Oh.
<set_>
Blah again.
<set_>
I am scared to use the BJT.
<ds2>
at the least, you need rail to rail part
<set_>
I need to look up rail to rail. Brb.
<ds2>
look up "rail to rail op-amp"
<set_>
I did...
<set_>
It looks like a common rail input voltage is required. 3.3v.
<set_>
I am thinking now that I know too little to handle this CMOS chip and builds around it. Thank you?
<set_>
Ha.
<set_>
I will need to research more!
<set_>
I have some MOSFETs.
<set_>
That may be better for switching compared to the BJT.
<set_>
Oh well. Until another time? I am beat.
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