LED to ground?

Hello again. Trying to do alittle in house project at work. Im trying to make alittle test box to use as smema on some of our projects here. I was wondering is there anyway to use a triple A or double A or 9 volt battery to power an LED? But I need the LED to come on when my PLC refernces it to ground. I need to do it this way cause of the way the SMEMA standard is. Is it possible? What do I have to figure out for the size of LED if it is possible? Any equations or anything would be nice.

Thanks for your time and help.

Joshua

I think LED comes with a current rating. If that is the case use 0.7-volt drop across the LED for calculation purpose.
You will need a series resistor equal to (V supply – 0.7 V) / (LED current).

First of all LEDs use different materials than
standard silicon diodes and have different voltage drop.
Typical voltage drop for LEDs is about 1.9-2.3V.
Typical LED current is 10-20mA while OLED (organic LEDs)
are ok with 2mA. Special purpose LEDs such as infrared
ones used in remote controls etc. are powered by higher
current (100-150mA) but of course this requires pulsed
regime not continuoous operation (they need time to
cool down the PN junction).
If you want to use standard el-cheapo LED and power it
from 9V battery, you must use resistor in series with
the LED. So if you want 15mA to flow through it and
assuming 2.2V voltage drop on LED, 6.8V will remain on
resistor.
6.8/0.015=453.3333
so next closest value is 470 Ohm.
If you use OLED and you would rather have 2mA,
calculated value for resistor comes to 3400 Ohm.
Closest reasonable value is 3.3kOhm.
Be carefull to select proper power rating for your
resistor in case you intend to run the LED on higher
voltage such as 24V (which is common when using PLC).
(24-2.2)Volt*0.015Amp=0.317Watt
So reasonable power rating in this case would be 0.5Watt.
Common 1/4Watt resistor would be stressed too much and
probably fail after some time.

panic mode

Thanks

Ok great. I think that did it. That helps out alot guys. Thanks for your time. Have a great day.

joshua

Oppppsss!!!!

Ok now that I have the voltge down and all. Im limited to only using 4 pins on a cannon plug and basically I need this LED to turn on when the PLC references it to ground. The common on the PLC is ground. If using a 9 volt battery. there is no way of getting my negitive side of the battery to ground. It wont work then will it? Just wondering. I think Im trying to do something that cant be done the way I want with what Im able to work with. But any advice will help thank you.

joshua

Just Wondering

What is "SMEMA"?

Check out acronymfinder.com for these "mysterious" acronyms

Surface Mount Equipment Manufacturers Association?

SMEMA

As the post before said. Here is a lil introduction. The SMEMA machine interface standards were developed to facilitate the interface of equipment used in the manufacture of surface-mounted printed circuit boards. So thats about it.. just gives specifics on like heigth of the conveyers and junk. Plus how to the machines talk to one another. basically they use 4 pins and you can interchange them and things. nothing special..

OK back to getting help

So is there anyway of getting an LED to work not using the negative post on the 9volt battery and just using a ground on a machine thru a plc. You cant unless you hook up the 9volt negative to ground no?

Why don't you tell us what is the PLC that you
have and what is the output type (output module
type number)? Is it sink or source or relay output?
It looks to me that you would like to use ground as
one of the terminals (or you mean DC Common?)...
Whatever it is you need to know potentials.
Some guys ground positive end of power supply
(like our good old customer Honda).

Is it that you do not have enough wires in the connector that you have to do what you want to accomplis?

The more detail you give us, the better quality the answer you will receive, and will eliminate some of the guess work!

Ok lets try this

Im just going to show you with a quick drawing. Im pretty certain I cant do this cause I can only use this one pin.. and this one output.. so I just dont think it will work but I will let you guys see it.

Thanks again for your time.

Ok, first of all you will need that second wire
for your LED circuit. Wether you can use one of the
other wires on that connector as return path is another
story. Maybe if you answer some of the question
we will be able to help you more:
1. what is the exact model of your PLC?
2. how many pins you have on that connector?
3. what exactly(!) are signals on the other pins?
4. are any other outputs wired to same connector?
5. do you have any other power line on that connector?
(dc common, positive or negative rail of whatever voltage...)

panic mode

Since some rural power authorities feel it's 'OK' to use ground as the return for 12.7KV, you should be OK using ground for the return on your 9V circuit...

beerchug

-Eric

Kreutzer:

think of your PLC output as if there is a normally-open relay contact between COM and Y1. Does it make sense now? Just connect your negative battery post to PLC's COM terminal and voila! you got yourself a complete circuit!

Now, the pitfalls. There might be a real relay inside, but not necessarily. That's why you were asked about the particular PLC model you are using. If, instead of a relay, there is a transistor inside, the polarity becomes important (unlike mechanical relay contacts, transistors conduct current only in one direction). You may end up switching wires of your battery and the LED.

There must be a resistor in series with the LED. The value of the resistor should be 9V / 20 mA = 450 Ohm. You may pick a 750 Ohm resistor and it should work. The resistor power rating is 9V * 20 mA = 0.18 Watt. Pick a standard 1/4 Watt size or larger. Thanks to Messrs. Ohm and Joule for discovering all that...

"SMEMA" is Surface-Mount Equipment Manufacturers Association. SMEMA 1.2 protocol is de-facto standard in printed-circuit board manufacturing, where production is usually done on long lines containing a variety of equipment from different manufacturers: bare board loaders, conveyors, paste dispensers, chip and component placers, ovens, stackers, buffers, shuttlegates, turntables etc., etc.
The protocol defines what does it take to make all this stuff work together. In addition to board transfer heights and other mechanical considerations, it defines a set of two discreet signals, going each direction along the line: upstream and downstream. Any two adjacent pieces of equipment are connected with at least four wires (although the standard connector is 14-pin round plastic AMP). A "previous" unit sets a signal whenever it has a board ready to move to the "next". The "next" unit sets a signal whenever it is ready to accept a board. There are some timing diagrams to follow.

Despite its simplicity, almost any "SMEMA-compatible" manufacturer manages to screw it up in its own way. Been there, done that...