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Re: Scope is working - isn't working - heck I don't know....

Stefan Trethan
 

On Fri, 05 May 2006 00:24:51 +0200, lcdpublishing <lcdpublishing@...> wrote:



The only thing I can think of is something I remember my father

doing years ago on a television set with a mechanical tuner. When

it wouldn't tune a channel, he would spray contact cleaner on the

tuner and life was good again. I am wondering if it is possible

that some of the quirks of this thing could be caused by dirty

contacts and such?


I don't have contact cleaner on hand, and I don't know enough about

this thing to start squirting chemicals in it to see if it helps or

not.

DON'T just put anything in there unless you KNOW it WILL do some good, because most likely otherwise it WILL do some DAMAGE.
Many contact cleaners are supposed to be removed again after application, so if you just spray it in there into places you will never be able to get access to without having to take the whole thing completely apart - which probably leaves you with a few boxes of spare components - you are gonna be in trouble.
Some of these circuits can be high impedance, so any leakage is BAD. I have been there, done that, with fluke multimeters. I thought it would be clever to spray some contact cleaner into the switch matrix that was acting up. Well, the whole thing leaked like a sieve after that (if that comparision is appropriate electrically), you guess how good that is with high impedance precision meter circuits. I ended up having to wash the thing several times with really hot water and detergents, and then alcohol, then bake dry it, to get things somewhat similar to normal again.

So if there is a bad pot or switch, get right in there to get it out or at least somehow separate it from the rest to service it. Because if you just spray in stuff from afar you are likely to have to take it all apart anyway and work on much more than only the faulty component.

If it is a bad contact you can identify it by wiggling at the attached knob, usually.


It is hard to say what exactly is wrong or right with the thing from afar, but doing some of the test procedures from the manual couldn't hurt?

ST
Re: RE : Scope is working - isn't working - heck I don't know....

 

Which two scopes do you have RObert?

I may be looking for one soon :-)


--- In Electronics_101@..., Robert Hedan
<robert.hedan@...> wrote:

A contact is a contact, it doesn't really matter where it is, you
KNOW it's
going to accumulate dirt, dust, debris and potatoe chips over time.

You think you're stupid, I've got 2 used scopes from EBay and they
both
work. D'uh...

I'd be hesitant about spraying stuff in the innards as well. But
I'm sure
that contact cleaner would do it some good, especially when the
units might
have done some duty in dirty shops. then a blast of fresh air in
there
would help get the grit out.

But best thing would be to replace the pots altogether. I've
never opened
mine(s), but I would bet they are modular and you can remove a
board for
service. They wouldn't provide those fancy-shmancy service
schematics if
technicians couldn't get to the components.

Robert
:)



-----Message d'origine-----
De : Electronics_101@...
[mailto:Electronics_101@...] De la part de
lcdpublishing
Envoy¨¦ : mai 4 2006 18:25
? : Electronics_101@...
Objet : [Electronics_101] Scope is working - isn't working -
heck I don't know....


Hi Guys,
...

The only thing I can think of is something I remember my father
doing years ago on a television set with a mechanical tuner.
When
it wouldn't tune a channel, he would spray contact cleaner on
the
tuner and life was good again. I am wondering if it is possible
that some of the quirks of this thing could be caused by dirty
contacts and such?
....

Chris
RE : Scope is working - isn't working - heck I don't know....

 

A contact is a contact, it doesn't really matter where it is, you KNOW it's
going to accumulate dirt, dust, debris and potatoe chips over time.

You think you're stupid, I've got 2 used scopes from EBay and they both
work. D'uh...

I'd be hesitant about spraying stuff in the innards as well. But I'm sure
that contact cleaner would do it some good, especially when the units might
have done some duty in dirty shops. then a blast of fresh air in there
would help get the grit out.

But best thing would be to replace the pots altogether. I've never opened
mine(s), but I would bet they are modular and you can remove a board for
service. They wouldn't provide those fancy-shmancy service schematics if
technicians couldn't get to the components.

Robert
:)

-----Message d'origine-----
De : Electronics_101@...
[mailto:Electronics_101@...] De la part de lcdpublishing
Envoy¨¦ : mai 4 2006 18:25
? : Electronics_101@...
Objet : [Electronics_101] Scope is working - isn't working -
heck I don't know....


Hi Guys,
...

The only thing I can think of is something I remember my father
doing years ago on a television set with a mechanical tuner. When
it wouldn't tune a channel, he would spray contact cleaner on the
tuner and life was good again. I am wondering if it is possible
that some of the quirks of this thing could be caused by dirty
contacts and such?
....

Chris
Scope is working - isn't working - heck I don't know....

 

Hi Guys,

A quick recap on my scope. I bought it off ebay last summer, used it
a couple times after fixing it. Don't panic, all I had to do was
make a know for the time/div switch.

Anyway, I can get the thing to calibrate and show me what I believe
to be a good signal. I have checked a few other things with it,
sometimes I get predictable results - what I believe to be a proper
series of dashes in the right places and for the right durations.

But, like today, I was looking at the serial output from the
max232. At 2400 baud, I could set the dials and see things they way
they should look. 4800 baud - good, 19200 baud - good, anything
above that and the signal lines either look like static or are so
hard to see I have to completely darkend the room I am in.

It also appears as though the triggering isn't always working
correctly. Sometimes it seems as though the traces are shown good,
then it seems to "Spaz out" for a while, then settles in again.

It also doesn't seem to repeat very well when I switch the time/div
dials and then come back to my original settings, often, I have to
wait a few seconds for it to get in "Synch" again, if it will at all.

Inside that thing is a "bazillion" gitzies, all of which scares the
crap out of me so working on it isn't really an option.

The only thing I can think of is something I remember my father
doing years ago on a television set with a mechanical tuner. When
it wouldn't tune a channel, he would spray contact cleaner on the
tuner and life was good again. I am wondering if it is possible
that some of the quirks of this thing could be caused by dirty
contacts and such?

I don't have contact cleaner on hand, and I don't know enough about
this thing to start squirting chemicals in it to see if it helps or
not.

I wouldn't mind selling it on E-bay as it certainly works better
than when I bought. But that takes me to the next step of getting
another one :-(

Chris
Re: Is there another type of... GRRRRRRRRRRRRRRRRR

 

I will be beating myself up over this for a long while - that was
just plain stupid! Especially for me who has a lot of experience
wiring up a whole variety of RS232 devices - GRRRRRRRRRRRRR!

ABout that scope, I am going to post another thread about it.

Thanks!
Chris



--- In Electronics_101@..., "Stefan Trethan"
<stefan_trethan@...> wrote:

Believe me you are not the first one to do this!

I spent much time of good hard thinking (and soldering) over that,
because
it can get really confusing with the what relative to what things.

I usually end up making a schematic with arrows ;-)

Anyway, it is working now, so stop hitting yourself, you fixed it!
Now wasn't that MUCH easier to figure out than even a tiny mistake
in
software? Thought so!

If your scope was operating(-ed) properly you'd see something
arriving at
the transmit pin of the avr when you send with the PC and start
scratching
your chin.

ST

On Thu, 04 May 2006 22:56:44 +0200, lcdpublishing
<lcdpublishing@...> wrote:

GRRRRRRRRRR. Stupid, Stupid, Stupid!


I see where I messed up and it is one of those "I couldn't be any

more stupid if I cut my head off" things!


I made the non-working board from the working circuit - copy and

paste and a little tweaking.


For the connection to the AVR I followed the legends on the
working

circuit board which has the two signals marked Tx and Rx. For
that

board, it was telling me what the pin does - relative to the
MAX232

not the AVR!
Re: Is there another type of... GRRRRRRRRRRRRRRRRR

Stefan Trethan
 

Believe me you are not the first one to do this!

I spent much time of good hard thinking (and soldering) over that, because it can get really confusing with the what relative to what things.

I usually end up making a schematic with arrows ;-)

Anyway, it is working now, so stop hitting yourself, you fixed it!
Now wasn't that MUCH easier to figure out than even a tiny mistake in software? Thought so!

If your scope was operating(-ed) properly you'd see something arriving at the transmit pin of the avr when you send with the PC and start scratching your chin.

ST

On Thu, 04 May 2006 22:56:44 +0200, lcdpublishing <lcdpublishing@...> wrote:

GRRRRRRRRRR. Stupid, Stupid, Stupid!


I see where I messed up and it is one of those "I couldn't be any

more stupid if I cut my head off" things!


I made the non-working board from the working circuit - copy and

paste and a little tweaking.


For the connection to the AVR I followed the legends on the working

circuit board which has the two signals marked Tx and Rx. For that

board, it was telling me what the pin does - relative to the MAX232

not the AVR!
Re: CLosed loop motor control ?

Stefan Trethan
 

On Thu, 04 May 2006 23:43:51 +0200, Peter Homann <groups@...> wrote:

Hi Stefan,


I think we are basically in agreement, and I am by no way a control loop

expert so I'm happy to be corrected.


The intent of my late night post (That's my excuse and I'm sticking to it)

was to make Chris aware that a lot of the text on the net covers position

control loops where the output signal is 0 when the desired position is

reached, whereas in a velocity control loop, this is not the case.


Cheers,


Peter.

Yes, we are somewhere in the same ballpark.
For the specific case we both agree the controller must look something like Vc=Vc + other components for this case of the spindle, while for a position the Vc would not be added. IMO those "other components" can still be PID, PD, or whatever, depending on situation, which didn't quite come out in your post as i understood it.
But as you say there is plenty on the web for those.


Anyway, it will be pretty obvious if one tries to use the wrong algorithm...

I personally am much more comfortable building control loops in hardware. But then, i'm much more comfortable with doing almost anything in hardware ;-)

ST
Re: CLosed loop motor control ?

 

Hi Stefan,

I think we are basically in agreement, and I am by no way a control loop
expert so I'm happy to be corrected.

The intent of my late night post (That's my excuse and I'm sticking to it)
was to make Chris aware that a lot of the text on the net covers position
control loops where the output signal is 0 when the desired position is
reached, whereas in a velocity control loop, this is not the case.

Cheers,

Peter.


Stefan Trethan said:

On Thu, 04 May 2006 22:38:08 +0200, Peter Homann
<groups@...> wrote:

Stefan,


It was late. The Kpd was my lazy way of writing (Kp*E + Kd*E)
I don't do digital controllers, only hardware, but this still doesn't seem
right to me since Kd would need to have a different effect to Kp, but
since this is not what we are discussing let's just ignore it and accept
there are P and D components in both cases, however they may be
implemented.



Basically in a velocity control loop, when the actual velocity is equal
to the

desired velocity, the control signal output is whatever value is
required to

maintain the current speed. (75% PWM for a speed of say 2000rpm)



In a position control loop the output signal is zero when the desired
position

is reached.


The I term is there to compensate for the drag in the system when the
control

voltage is very small as we are almost there. In this case the I term
winds up

(increases the control signal) until the desired position is reached as
the E

term is so small.


In a Velocity control system, this problem does not exist as the error
value

is always added to the current value of the control signal, effectively
doing

what the I term would do anyway.


If you write out the velocity algorithm fully you will find the the I
term is

redundant.


Cheers,


Peter

I see what you are saying now.
But i would still not agree 100%.
You basically differentiate "velocity" and "position" by the type of the
process (if it is a integrating process or a proportional one, in other
words "decrease-stay-increase" input versus "low-medium-high", both in a
linear fashion).
Both types of processes _can_ be controlled by PID, but if the process is
integrating you may not need a I term and it can lead to oscillations to
have one. That said, i still think there is a mixup in your original post:

you want to implementa velocity control loop, not position control loop.
Therefore you don't haveany I term, just P and D.
I think this statement above is wrong.
In the next statement you seem to have it right:


The difference is that in a velocity control system you are adding or
subtracting the error signal to the currently set control signal.
Vc = Vc + Kpd*E
Has I term, correct, but above you said it has not.

In a position control system the control signal is set to the value of
errorsignal.
Vc = Kpd*E
Has no I term.

So you see, there's at least a problem there. But really i disagree on the
more fundamental point that a integrating process never can/should have a
PID controller. For example if you imagine again the position control in
your head, you get close to the target, but friction and stuff prevents to
move the process "spot on" with the little tiny error signal amplified
only by Kp. If you have a integrating component in the controller you can
eliminate all the error.
OTOH imagine the spindle - it can be controlled with a PD controller
without I also. Imagine the RPM dropping 1000RPM because of load. The P
term amplifies the error to correct this up again by 900RPM, 100RPM error
- small remaining error is normal with PD control. So you see where i'm
coming from.

ST








Yahoo! Groups Links
Re: CLosed loop motor control ?

Stefan Trethan
 

On Thu, 04 May 2006 22:38:08 +0200, Peter Homann <groups@...> wrote:

Stefan,


It was late. The Kpd was my lazy way of writing (Kp*E + Kd*E)
I don't do digital controllers, only hardware, but this still doesn't seem right to me since Kd would need to have a different effect to Kp, but since this is not what we are discussing let's just ignore it and accept there are P and D components in both cases, however they may be implemented.



Basically in a velocity control loop, when the actual velocity is equal to the

desired velocity, the control signal output is whatever value is required to

maintain the current speed. (75% PWM for a speed of say 2000rpm)



In a position control loop the output signal is zero when the desired position

is reached.


The I term is there to compensate for the drag in the system when the control

voltage is very small as we are almost there. In this case the I term winds up

(increases the control signal) until the desired position is reached as the E

term is so small.


In a Velocity control system, this problem does not exist as the error value

is always added to the current value of the control signal, effectively doing

what the I term would do anyway.


If you write out the velocity algorithm fully you will find the the I term is

redundant.


Cheers,


Peter

I see what you are saying now.
But i would still not agree 100%.
You basically differentiate "velocity" and "position" by the type of the process (if it is a integrating process or a proportional one, in other words "decrease-stay-increase" input versus "low-medium-high", both in a linear fashion).
Both types of processes _can_ be controlled by PID, but if the process is integrating you may not need a I term and it can lead to oscillations to have one. That said, i still think there is a mixup in your original post:

you want to implementa velocity control loop, not position control loop. Therefore you don't haveany I term, just P and D.
I think this statement above is wrong.
In the next statement you seem to have it right:


The difference is that in a velocity control system you are adding or subtracting the error signal to the currently set control signal.
Vc = Vc + Kpd*E
Has I term, correct, but above you said it has not.

In a position control system the control signal is set to the value of errorsignal.
Vc = Kpd*E
Has no I term.

So you see, there's at least a problem there. But really i disagree on the more fundamental point that a integrating process never can/should have a PID controller. For example if you imagine again the position control in your head, you get close to the target, but friction and stuff prevents to move the process "spot on" with the little tiny error signal amplified only by Kp. If you have a integrating component in the controller you can eliminate all the error.
OTOH imagine the spindle - it can be controlled with a PD controller without I also. Imagine the RPM dropping 1000RPM because of load. The P term amplifies the error to correct this up again by 900RPM, 100RPM error - small remaining error is normal with PD control. So you see where i'm coming from.

ST
Re: Is there another type of... GRRRRRRRRRRRRRRRRR

 

GRRRRRRRRRR. Stupid, Stupid, Stupid!

I see where I messed up and it is one of those "I couldn't be any
more stupid if I cut my head off" things!

I made the non-working board from the working circuit - copy and
paste and a little tweaking.

For the connection to the AVR I followed the legends on the working
circuit board which has the two signals marked Tx and Rx. For that
board, it was telling me what the pin does - relative to the MAX232
not the AVR!

So, I drilled out the traces on the Tx and Rx signals betwen the AVR
and the MAX232, wired in some cross-over jumpers, connected it all
back up again and viola! Things work - well, atleast my RS-232
tester thing is flashing the right lights.

GRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR

Thump, thump, thump, thump, thump.... (sound of kicking self in butt)

Chris
Re: CLosed loop motor control ?

 

Stefan,

It was late. The Kpd was my lazy way of writing (Kp*E + Kd*E)

Basically in a velocity control loop, when the actual velocity is equal to the desired velocity, the control signal output is whatever value is required to maintain the current speed. (75% PWM for a speed of say 2000rpm)


In a position control loop the output signal is zero when the desired position is reached.

The I term is there to compensate for the drag in the system when the control voltage is very small as we are almost there. In this case the I term winds up (increases the control signal) until the desired position is reached as the E term is so small.

In a Velocity control system, this problem does not exist as the error value is always added to the current value of the control signal, effectively doing what the I term would do anyway.

If you write out the velocity algorithm fully you will find the the I term is redundant.

Cheers,

Peter




Stefan Trethan wrote:

On Thu, 04 May 2006 15:04:28 +0200, Peter Homann <groups@...> wrote:

Vc = Vc + Kpd*E

Vc = Kpd*E
To me this seems like a PI vs. a P control.
I don't quite see what it has to do with velocity vs. position?
I would say a PID can be used for RPM control as well, what is wrong with integrating the error out to zero here?
ST
Yahoo! Groups Links
--
------------------------------------------------------------------
Web: www.homanndesigns.com
email: homann@...
Phone: +61 421 601 665
www.homanndesigns.com/ModIO.html - Modbus Interface Unit
www.homanndesigns.com/DigiSpeedDeal.html - DC Spindle control
www.homanndesigns.com/TurboTaig.html - Taig Mill Upgrade board
Re: Is there another type of cap that looks like electrolyt...

 

Caps are rulled out I think. I have tried 1uf 50V, 10uf 50V, 10uf
35V, and 10uf 24volt. If I put the darn things in backwards, I
would have had to do it the same backwards way 5 times in a row.
Although, that is entirely possible for me :-(

I have posted a layout in the files section. It's a very small
circuit board with only a couple components on it.

files - chris-lcd IOinterfaceunit.pdf.

I am 99% sure it is something obviously stupid, I am just too stupid
to see it :-)

Chris





--- In Electronics_101@..., JanRwl@... wrote:


In a message dated 5/4/2006 1:48:19 P.M. Central Daylight Time,
lcdpublishing@... writes:

Any ideas? Any chance I have the wrong type of CAPS?



Chris: I have NO business responding to this inquiry as I have
NO idea what
your circuit is or looks like, BUT I would assume if it's the
caps, the
problem would "move" with the caps. Have you tried TESTING
them? Set your DVM
on the LO-ohm range and test a known-good cap with the probes ONE
way, then
SWAPPED, and note the changes in the reading. Then see if the
changes are
similar for the suspect cap. Better: Use a cap. tester! A
SHORTED cap, or OPEN
cap would probably be causing your problem! JRR
Re: Is there another type of cap that looks like electrolytic but behaves differ

Roy J. Tellason
 

On Thursday 04 May 2006 03:19 pm, rtstofer wrote:
For both devices, the proper value for the capacitors is 1 ufd, not 10
ufd.
Hey Chris, you want me to send you some? I have a *pile* of those here ,
1uF/50V...

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
Re: Is there another type of cap that looks like electrolytic but behaves differ

 

I just posted a layout for this circuit board in the files section

FILES -> Chris-LCD -> IO InterfaceUnit.PDF

If someone could take a look at it just to make sure I didn't do
something really stupid!

Chris
Re: Is there another type of cap that looks like electrolytic but behaves different?

 

The caps are in the correct way. These particular caps have the
band and - sign on the negative lead - very clearly marked.

The caps on the board that is working don't have any indication of
which way is which (That I can figure out for certain). I assumed
that the writing was on the negative lead side - it worked so I
didn't give it any more thought.






--- In Electronics_101@..., 2alan.metcalf@... wrote:

Hi

Are the caps from Jameco or Digikey connected the wrong way
round. some
makers indicate the negative terminal, some indicate the positive
terminal?

Alan


From: "lcdpublishing" <lcdpublishing@...>
Date sent: Thu, 04 May 2006 18:43:43 -0000
S> Hi Guys,

I am losing a lot of hair on this one.

I have two PCBs that both have MAX232 chips. One is a cpe the
other
has an N suffix. That part really doesn't matter as I have
swapped
the chips back and forth (they are in sockets) a number of times
and
the problem doesn't follow.

Both PCBs have 10 uf caps. One boad has caps from Radio shack -
it
works. The other board has caps from Jameco or Digikey, not
sure.
Either way, they ARE marked 10uf 50V.

Both circuits are very close to being the same. The difference
being the caps on the working board are about 1/2" further away
from
the max 232.

I have swapped out the caps on the non-working board - still
didn't
fix it.

I have done a pin-by-pin comparison about 5 or 6 times now and I
can't find any differnce in the two circuits.

I tried to connect my scope up to do some signal comparisons, I
have
a hunch my scope isn't working properly at all - don't want to
try
and figure it out at this time - don't know how for that
matter :-(

The only thing I can think of is that the caps on the non-
working
board are of some other type. I don't have any others on hand
so I
can't even do any more swapping.

As to what is not working, I am getting nothing out of the
max232.
The Tx pin is at -9.67 volts and seems to vary .01 volts during
transmission(I am using a digital meter and can't tell for
sure).

The Rx pin is at 0 volts.

From the AVRs RX pin as measured at the MAX232 I get 5 Volts
steady.

From the AVRs TX pin, as measured at the MAX232 I get 5 volts,
but
can see the voltage dropping during transmision - drops about .3
volts as best I can tell with the meter.

To make sure the problem isn't on the PCB somehow affecting the
AVR,
I used jumper wires from the MAX232 on the non-working board,
fed
the Tx / Rx from the AVR to the working board and communications
is
good.

I am stumped - but then again, this is to be expected as I don't
know how to check anything else.

Any ideas? Any chance I have the wrong type of CAPS?

Chris
Re: Is there another type of cap that looks like electrolytic but behaves differ

Leon Heller
 

----- Original Message -----
From: "rtstofer" <rstofer@...>
To: <Electronics_101@...>
Sent: Thursday, May 04, 2006 8:19 PM
Subject: [Electronics_101] Re: Is there another type of cap that looks like electrolytic but behaves differ


--- In Electronics_101@..., "lcdpublishing"
<lcdpublishing@...> wrote:

Hi Guys,

I am losing a lot of hair on this one.

I have two PCBs that both have MAX232 chips. One is a cpe the other
has an N suffix. That part really doesn't matter as I have swapped
the chips back and forth (they are in sockets) a number of times and
the problem doesn't follow.

Both PCBs have 10 uf caps. One boad has caps from Radio shack - it
works. The other board has caps from Jameco or Digikey, not sure.
Either way, they ARE marked 10uf 50V.
For both devices, the proper value for the capacitors is 1 ufd, not 10
ufd.

For the MAX232N: pin 2 should be +8.5V and pin 6 should be -8.5V if
the charge pumps are working.

For the MAX232CPE: the datasheet says +10V and -10V on the same pins.

10 uF will be OK. The non-working ones might be tantalum, the line on them sometimes indicates the +ve lead.

Leon

---
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Re: multi volt vehicle unit

 

¿ªÔÆÌåÓý

Thank you much!? Just stumbled onto a Digikey catalog ¨C boy there¡¯s lots of cool stuff there!? Pressure transducers, IR LEDS, dc/dc regulators¡­now all I need it time ¨C winter just wasn¡¯t long enough.? Although it would have been longer had I not been distracted by the Inventeams and FIRST robotics that I mentored ¨C cool stuff for kids ¨C even us 50+ kids.? Thanks again. C

?

Chuck Merja

Lemelson-MIT Inventeams -

US FIRST Robotics -

lat/long 47.52383? -111.67912

211 Adams Rd

Sun River, MT 59483

vx?? 406.264.5955

cell? 406.799.5955

fax?? 406.264.5830

?

From: Electronics_101@... [mailto:Electronics_101@...] On Behalf Of Roy J. Tellason
Sent: Wednesday, May 03, 2006 5:02 PM
To: Electronics_101@...
Subject: Re: [Electronics_101] multi volt vehicle unit

?

On Wednesday 03 May 2006 06:07 pm, Chuck Merja wrote:
> A while back this list discussed a benchtop multiple voltage supply.? I am
> a farm kid who likes gadgets and am frustrated by all the individual
> voltage adapters I need to plug into the cig lighter, so I am looking for
> something to probably hardwire into a rig that will supply these various
> voltages.
>
> Right now I use PDA (5v 2A), Panasonic Laptop CF27 (10.8 V at 1? Amp) and
> GPS 12 v at an Amp.? I would also like to have a small diode protected
> backup battery, so that when I start the engine the GPS won't drop out.
> Both the laptop and PDA have bats in them, so I'm not too worried about
> them.? I've used several separate devices, but none is very satisfactory,
> and the 5V deal is now supplied by 12v to 110v inverter, then through a
> wall wart back down to 5V - well, it works and better than the variable
> voltage converters that I've let the smoke out of for one reason or
> another.
>
> I see several voltage converters, but nothing that fits the whole bill, by
> itself.
>
> Anyway, I guess I could build something, but I'm really a mechanical guy
> not an electronics guy - but am kinda an electronics wannabe.? Any
> suggestions - volunteers?

For the 5V supply that's easy,? you can do it with a single part more or less,?
but for 2A the common 7805 won't cut it -- you'll need a bit more oomph.? Try
the LM323 or LM350,? both of which are in TO-3 cases,? and which should
probably be mounted on a heatsink,? since dropping 7V at 2A means it's going
to be dissipating 14W,? more if the charging system on the vehicle pushes the
voltage up a bit.

For the 10.8V,? I'd suggest the LM317,? which is an adjustable regulator that
you set up with a couple of resistors to set your output voltage.? This is
also available in the TO-3 case though for only around an amp or so you can
probably get away with the TO-220 case version,? but I'd still use a
heatsink,? since it's dissipating a couple of watts.

The 12V?? That depends,? you can perhaps use the incoming DC power as is from
the vehicle with some filtering and conditining,? sometimes the charging
voltage of a vehicle will push that upwards some and you may run into the
limits of some of the components.? That could get a little bit tricky,? but
maybe a zener diode and a series resistor would take care of it.

With the regulator chips,? you will want some capacitors at the input and
output,? and with the LM317 you need to keep the case of the device isolated
from the vehicle ground,? but that't not hard to do.? For details of the use
of these parts the datasheets are usually pretty good with all sorts of
examples,? and I'd recommend that you search them out and see what all is in
them.? The ones from National Semiconductor are pretty good,? if you have a
choice of brands.

If you get stuck on any of this,? feel free to post in here and one or another
of us will have something to say on the subject,? I'm sure.? :-)

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,? a critter that can
be killed but can't be tamed.? --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
Re: Is there another type of cap that looks like electrolytic but behaves different?

[email protected]
 

Hi

Are the caps from Jameco or Digikey connected the wrong way round. some
makers indicate the negative terminal, some indicate the positive terminal?

Alan


From: "lcdpublishing" <lcdpublishing@...>
Date sent: Thu, 04 May 2006 18:43:43 -0000
S> Hi Guys,


I am losing a lot of hair on this one.

I have two PCBs that both have MAX232 chips. One is a cpe the other
has an N suffix. That part really doesn't matter as I have swapped
the chips back and forth (they are in sockets) a number of times and
the problem doesn't follow.

Both PCBs have 10 uf caps. One boad has caps from Radio shack - it
works. The other board has caps from Jameco or Digikey, not sure.
Either way, they ARE marked 10uf 50V.

Both circuits are very close to being the same. The difference
being the caps on the working board are about 1/2" further away from
the max 232.

I have swapped out the caps on the non-working board - still didn't
fix it.

I have done a pin-by-pin comparison about 5 or 6 times now and I
can't find any differnce in the two circuits.

I tried to connect my scope up to do some signal comparisons, I have
a hunch my scope isn't working properly at all - don't want to try
and figure it out at this time - don't know how for that matter :-(

The only thing I can think of is that the caps on the non-working
board are of some other type. I don't have any others on hand so I
can't even do any more swapping.

As to what is not working, I am getting nothing out of the max232.
The Tx pin is at -9.67 volts and seems to vary .01 volts during
transmission(I am using a digital meter and can't tell for sure).

The Rx pin is at 0 volts.

From the AVRs RX pin as measured at the MAX232 I get 5 Volts steady.

From the AVRs TX pin, as measured at the MAX232 I get 5 volts, but
can see the voltage dropping during transmision - drops about .3
volts as best I can tell with the meter.

To make sure the problem isn't on the PCB somehow affecting the AVR,
I used jumper wires from the MAX232 on the non-working board, fed
the Tx / Rx from the AVR to the working board and communications is
good.

I am stumped - but then again, this is to be expected as I don't
know how to check anything else.

Any ideas? Any chance I have the wrong type of CAPS?

Chris
Re: Is there another type of cap that looks like electrolytic but behaves differ

 

--- In Electronics_101@..., "lcdpublishing"
<lcdpublishing@...> wrote:

Hi Guys,

I am losing a lot of hair on this one.

I have two PCBs that both have MAX232 chips. One is a cpe the other
has an N suffix. That part really doesn't matter as I have swapped
the chips back and forth (they are in sockets) a number of times and
the problem doesn't follow.

Both PCBs have 10 uf caps. One boad has caps from Radio shack - it
works. The other board has caps from Jameco or Digikey, not sure.
Either way, they ARE marked 10uf 50V.
For both devices, the proper value for the capacitors is 1 ufd, not 10
ufd.

For the MAX232N: pin 2 should be +8.5V and pin 6 should be -8.5V if
the charge pumps are working.

For the MAX232CPE: the datasheet says +10V and -10V on the same pins.

Richard
Re: Is there another type of cap that looks like electrolytic but behaves different?

Leon Heller
 

----- Original Message -----
From: "lcdpublishing" <lcdpublishing@...>
To: <Electronics_101@...>
Sent: Thursday, May 04, 2006 7:43 PM
Subject: [Electronics_101] Is there another type of cap that looks like electrolytic but behaves different?


Hi Guys,

I am losing a lot of hair on this one.

I have two PCBs that both have MAX232 chips. One is a cpe the other
has an N suffix. That part really doesn't matter as I have swapped
the chips back and forth (they are in sockets) a number of times and
the problem doesn't follow.

Both PCBs have 10 uf caps. One boad has caps from Radio shack - it
works. The other board has caps from Jameco or Digikey, not sure.
Either way, they ARE marked 10uf 50V.

Both circuits are very close to being the same. The difference
being the caps on the working board are about 1/2" further away from
the max 232.

I have swapped out the caps on the non-working board - still didn't
fix it.

I have done a pin-by-pin comparison about 5 or 6 times now and I
can't find any differnce in the two circuits.

I tried to connect my scope up to do some signal comparisons, I have
a hunch my scope isn't working properly at all - don't want to try
and figure it out at this time - don't know how for that matter :-(

The only thing I can think of is that the caps on the non-working
board are of some other type. I don't have any others on hand so I
can't even do any more swapping.

As to what is not working, I am getting nothing out of the max232.
The Tx pin is at -9.67 volts and seems to vary .01 volts during
transmission(I am using a digital meter and can't tell for sure).

The Rx pin is at 0 volts.

From the AVRs RX pin as measured at the MAX232 I get 5 Volts steady.
From the AVRs TX pin, as measured at the MAX232 I get 5 volts, but
can see the voltage dropping during transmision - drops about .3
volts as best I can tell with the meter.

To make sure the problem isn't on the PCB somehow affecting the AVR,
I used jumper wires from the MAX232 on the non-working board, fed
the Tx / Rx from the AVR to the working board and communications is
good.

I am stumped - but then again, this is to be expected as I don't
know how to check anything else.

Any ideas? Any chance I have the wrong type of CAPS?


Check the voltages across the capacitors, you should be able to work out what is wrong. You might have them round the wrong way, for instance. Why not buy some MAX202s - they are easier to use as they work with 100 nF ceramic capacitors.

Leon

Leon
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