a seven-segment querry:)

On my application, i need a seven-segment display to indicate which doors closes since there are 59 doors to be installed.
Can i connect seven-segment display directly from PLC?
If yes, how?
Also, seven-segment display usually needs 5 V down. How will i lower this voltage so that my seven segment display will not burnt-out?

Pls. help

Can I connect seven-segment display directly from PLC?

Yes, if your PLC has a TTL Output module (5 VDC transistor-switched outputs).

How will i lower this voltage so that my seven segment display will not burnt-out?

You can buy BCD Output Interface Modules that are designed to interface between the PLC outputs and a 7-segment display. Usually they have built-in displays, with the electronic interface to allow connection to a variety of PLC outputs.

how many 7-seg display we are talking about? one for each door? how many digits per display? how many plc outputs you have? how far are the displays from plc?

you can use plc outputs to drive the naked 7-segment displays directly but you will need one output for each segment. the segments are just LEDs which are current driven. for example to use 24V PNP output, you can use any common cathode unit and just limit current with resistor.
since 2-3V drop is expected at 10mA (604-SC56-21GWA for example), you would only need 2.2k resistors, 1/4W or higher.
if using NPN, go for common anode displays.

http://www.mouser.com/catalog/catalogusd/638/81.pdf

but this is only practical for very few digits. if you need to drive more of them, you need better solution like multiplexing (still lot's of wiring).

for example using single 32 point output card you could drive 4 digits.
adding one more card (but opposite polarity) with say 16 outputs, you can multiply number of digits by 16 (16x4digit=64 digit).
that is only two very common cards although in this casde they have to be opposite polarity (one PNP, other NPN).
no additional resistors are needed for multiplexing but since each segment now only operates for a fraction of time, brightness will go down.
the workaround is to increase current by lowering resistors value (don't go crazy on this one or you will blow bunch of displays, I'd say stay within 20-25mA).

Panic mode,

i think il go with your suggestion. i only need 2 digits to count from 1-59..that means i only need an additional 16 out from PLC..tnx a lot

1 digit = 7 segments
1 output per segment = 7 outputs per digit
2 digits = 14 outputs needed.

(Also you need a lot of skill to wire them up).

On my application, I need a seven-segment display to indicate which doors close, since there are 59 doors to be installed.

Click to expand...

How do you plan to share ONE display with 59 doors? If more than 1 door is closed, what is your plan to show that?

You can multi-plex the output by having your PLC count from 1 to 59, displaying each number on the display. Then after the number, the next display shows either a 0 for open, or a 1 for closed, pause 3 seconds, then step to the next number.

Another method would be to use an additional ouput for a light. If the Display reads 1, and Door 1 is closed, then light turns on. When display steps to 2, and Door 2 is open, light goes off.

Hmm, i will put a priority in case all three barcodes scanned at the same time. Example, i will prioritize barcode 1, then barcode 2 and last is 3. So, when barcode 1 scans the corresponding door opens and 2 & 3 are on board. Meaning after all doors closes back, thats the time that the system will entertain barcodes 2 then 3 after.
I plan to place an indicator lamp on each door to show which door closes & opens.
The seven-segment will only be for confirmation that the reacted door is the same as its displayed value.
I hope i make a sense

Well, it is beginning to make a little sense. I see now that your bar code problem and your 7-segment display problem are both part of the same project.

It might help to practice describing a whole project. You start with the overall picture, then work down to the small details.

When you give out a few details and ask a question about that one little part, often you will not get a good answer, or a complete answer, and maybe you will get only wrong answers!

Try splitting it into sections in your question. You have plenty of room on this site to go into details like this:

A. My project is to (description here).

1. Part 1 is where I try to (description here).
2. Part 2 is where I want to (description here).
3. Part 3 is where I do (description here).

Q: How do I do Part 2?

I will put a priority in case all three barcodes scanned at the same time.

Click to expand...

You can also set up interrupts so that you can read each barcode as it is scanned, then save it to a temporary location, and recall the correct barcode when your program reaches the step for that particular location.

I have not worked with a barcode scanner in several years, but I think the scanner will have a feedback signal, so that when it sends a scan to the PLC, it will wait for an Acknowledge back from the PLC. Therefore, the scanner will hold until it receives the Acknowledge. Using that, you can read in many barcodes, one after the other.

Lancie1,

im sorry for not detailing the projects, my apology. But uv been very very helpful, tnx alot

HMI is definitely more flexible solution but I am not so sure about cheaper even if it's LCD character instead of graphic display.
Note that HMI needs comm port and cable too. If you don't have spare com port, this will definitely tip the scale regardless of price of HMI.

2-digit display is about $1 (I've bunch of 4-digit for $0.50) and spare output cards are usually kicking around.

Another possibility is to use counter and PTO output for example.

james patricio said:

how about using an HMI (GOT) to display any numbers u want... less wiring compared to 7-segment display. Compare the cost of 2-digit 7-segment display plus 14 to 16 points extension output module against the cheaper HMI?

Click to expand...

James,

I agree that using an HMI would definitely give me the beneftis of not having "Forest wiring". But here in the Philippines, HMI is pretty much expensive..

panic mode said:

Another possibility is to use counter and PTO output for example.

Click to expand...

Panic mode of Toronto,

I'm a little interested with the use of a counter & PTO (hmm, sorry to sound naive but PTO stands for?).
Could you discuss further?
I hope you don't mind


Best Regards,
theripley

PTO = pulse train output

this is commonly used to drive stepper or servo drives and just about all small PLCs have it, larger ones usually require dedicated card. if you have free PTO and one more spare output, all you need is counter (~$50).

using PTO and fast counter you only need two PLC outputs:
- reset (to clear counter)
- PTO (to send number of pulses)

should be obvious but just to mention - beware of counter speed. this makes sense only if counter can count fast.