The classic polarity reversing is usually a motor hooked up to a DPDT
switch, like this:
Replace the switch with a 2x3 header and a couple of jumpers, and you're
good to go.
Tony
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-----Original Message-----
From: [email protected] <[email protected]> On Behalf
Of Dave
Sent: Sunday, 15 November 2020 6:49 AM
To: [email protected]
Subject: Re: [homebrewpcbs] Circuits on 2 sides
I was thinking something like that with the multiple jumpers or those 2
position switch banks but that would be overkill (the dip switches). I
just
wasn't sure how to draw it up. I like good habits though. :) I like the
idea that
you presented as I thought it could be done with simple jumpers and the
solder idea makes it even better. Of course wiring it correct in the first
place
makes it best. I did a little reading on 0 ohm resistors yesterday. Always
something to learn. It never ends. That is the fun part though.
Thanks,
Dave
On 11/14/2020 1:28 PM, Harvey White wrote:
Ok, just trying to encourage good habits.? You might want to consider
putting a silk screen outline of the part (you draw it) on the board,
or add two spdt style (middle with two ends) jumper pads hooked up to
reverse the polarity if both are shorted in one position, and not
reverse the polarity if both are shorted in the other position.? This,
of course, goes to the diode and will allow you to use normal LEDS as
well as the reversed one.? It does add an extra step, but allows more
of a "just make it like the drawing" assembly, which is very
frequently a good thing.
The same technique can be used to control the state of address pins,
write enable pins, and the like *if* the pins can tolerate a direct
connection to vcc.? If not (TTL would be an example where you'd want a
1K series resistor, old design practice here), then put in the
appropriate resistors. You could also just wire pullups to the pin and
use an SPST jumper to ground the pin when needed.
The jumpers look like resistor pads, but closer together. They're
designed to be shorted together with a solder blob.? I'd rather use
them than 0 ohm resistors because the resistors are an extra step.
You use the 0 ohm resistors if you want to run traces between the
pads.? Some manufacturers use 0 ohm resistors for configuration since
they use pick and place machines to put parts on the board.? Since
you're doing things by hand, that's not needed.
The closest I can come to a polarity switcher is the set of jumpers
above.
Harvey
On 11/14/2020 1:18 PM, Dave wrote:
Harvey,
? In my case the circuit is so simple no harm can be done but I do
get your point. From the batteries to a jack with a female plug.
Inside the box the jack is hardwired to the pcb. The only time it has
to be swapped is on assembly and is covered after that. What got me
in the beginning is that the IR led's I use have the anode and
cathode reversed so the flat on the LED is not the cathode or the
negative like 99% of the other led's out there. I always test them on
the breadboard but being my mind always thinks the negative is the
short lead, I have solder the red and black wires onto the led
incorrectly. Then as assembly continues it ends up backwards. It is
not a big deal though as now I have ordered some Dupont female pins
and housings to solve that issue if it ever comes up again. For the
most part I likely won't ever make the mistake again but was curious
if a polarity switcher was possible a device because they seem to
make everything.
Thanks,
Dave
On 11/14/2020 11:59 AM, Harvey White wrote:
I would not use reversing a connector for the fix of an LED
installed backwards.? I'd be very tempted to check them first. Most
of what I use has an index mark on it indicating the cathode.
If you have a board where you can plug in the power backwards, then
you have to think about how to plug in the power every time.
Thinking is a quantity noticeably absent as the hour for late night
debugging goes past 12 midnight.
One group of college students was in a robot competition, powering
their project with a high power lithium ion battery. They didn't key
the connector (for whatever reason), nor did they install any sort
of polarity protection, not even a fuse and a reverse biased diode.
Three hours from home on a Sunday and before the competition, they
plugged in the battery backwards and blew every power module in the
robot.? Even an early morning run for spare parts made no difference
to the outcome.
And that is why George always wear hat when visiting Tooki-Tooki
bird friends.
One of the tweezer probes with banana plugs and one of the parts
checkers (transistor/diode/LED/capacitor) can be used to identify an
LED before you put it in.? Since they run off 5 volts (regulated
from a 9 volt battery), you have enough voltage for blue and white
LEDS.? You can also get them with a PC board pattern that allows
directly putting SMT chips on the tester.
Harvey
On 11/14/2020 11:34 AM, Dave wrote:
Bertho,
? Funny story. :) But in my case I was hoping and also using my JST
connectors, there was a way to reverse polarity. Of course putting
together the project correct would be ideal, but in the past not
all LED's are properly configured as far as polarity. Once the
project is soldered up I have (only once or twice) had the polarity
backwards. The easy fix would be to unplug a connector and re-plug
it in opposite for the power feed. So far everything I have done
has been soldered so it makes it a little harder to fix but not
really that hard. But when I switch to plugs using JST connectors I
was just curious if there was a trick for future use just in case.
Like a few jumpers that could be swapped around. In the end I will
just pay attention and color code with wire colors etc.
Dave
On 11/13/2020 10:35 PM, Bertho wrote:
One trick is if you have a three pin connector is to use the
center pin for positive and the two outside pins connected to
ground. Then polarity does not matter.
Another common thing on multipin strip connectors is to remove a
male pin and insert a dummy plug in the matching female location.
If reversed, it will not plug in.
That reminds me.? A very long time ago we were manufacturing a
product with a 12 pin in line connector with a missing pin.? It
turns out that a square toothpick fit perfectly as a plug for the
female connector: Just push it all the way in and cut it off
flush.
We had an angry customer calling about our terrible quality: He
said there was even a piece of wood stuck in the connector and it
took him a long time to remove it.? Then even worse he said, when
he finally plugged it in there was smoke coming from the PCB and
it did not work.? Of course he had plugged it in backwards.
Bertho
