serial florecent display

[springer]

what PIC output circuit would i need to drive a 12v florescent display?

I've acquired an old but working 20 * 2 florescent display from an old POS till. its a 12v serial device that powers up and display's its welcome message etc...

I've fried one 18x already connecting this to the display, but the problem is that i dont know what sort of current i'm dealing with on the serial in line.

what resistor values should i try on the serial line?
should i tie the resistor to +Ve or -Ve, (5v or 12v) or should i be using transistor circuit?

Is there a simple guide to driving circuits with differing voltages?

If its any help the device came out of an old IBM pos till and has a model number of 52210112
Thanks... (that's a lot of questions for one post!)

 

[westaust55]

fluorescent driver circuit

Here is a circuit from an old copy of Silicon Chip mag as a starting point.

Another facet to consider.
While on mains we tend to operate fluorescent tubes at 50 or 60 Hz (becasue it is cheap in terms of equipment to so so), if you operate a fluorescent tube at around 400Hz you will get a higher light output.

http://www.siliconchip.com.au/cms/A_30504/article.html

Click on FIgure 1 in the web article and that takes you to all the pics in larger size. step thru till you get the the full circuit with component values.

 

[LizzieB]

Before anyone else suggests circuits for driving fluorescent lamps I'll remark that I believe the OP is actually looking for information about driving a Vacuum Fluorescent (data) Display.

 

[westaust55]

Lizzie,
Reading again in light of what you say, you are most likely right.

I read it as an old 20 Watt x 2 fluorescent tube type lamps (as opposed to new 18W x 2 tubes) , as oposed to 20 char x 2 line.

Goes to show how easy it is to head off at a tangent when the given nformation is not entirely clear.

 

[BeanieBots]

The the use of "serial" and "display" make it quite clear it's character display!
If it REALLY is a serial comms issue talking to a display that requires +/-12v to drive it, then a MAX232 should do the job but I'd be surprised if an "old" display from an old bit of kit is serial. Even if it is serial, the serial driver likely to be a seperate board within the "old" piece of kit.

 

[westaust55]

wrt "display"

Not here in Oz. In the context of a retail store, a "display" can be a counter or similar with or without lighting built into the top to illuminate the items on display.

Can easily believe as old equipment it could be serial comms. My first home printer (an Andex bought in the 1970's) has an RS232 port.

A search of the IBM worldwide website for POS equipment with a model number of 52210112 did not find anything. Nor did a general search (just found this thread ).

 

[springer]

It's a display, not a light!!!

sorry for any confusion in my original post, but what i was talking about is an alphanumeric vacuum fluorescent display.
its a three wire unit; +12v, 0v, and serial (9600,8,n,1).

So how would i protect the serial out pin of a PIC to drive this?

 

[BeanieBots]

You shouldn't need any protection when connecting a PICAXE output to ANY input.
An INPUT CANNOT source any current, so it can't cause damage.
Even if it has an internal pull-up resistor, it won't DAMAGE the PIC.

If the connection is causing damage, then you are not connecting to the right place or the unit is damaged.

Put a DVM on what you think is the serial input. (with it powered up).
What is the voltage?
Now put a 10k resistor between "input" and 0v. What is the voltage?
Move the resistor to between "input" and 12v, what is the voltage?

 

[hippy]

its a three wire unit; +12v, 0v, and serial (9600,8,n,1).

So how would i protect the serial out pin of a PIC to drive this?

As BeanieBot says, you shouldn't normally need to use any protection for a PICAXE output to another input, but what "serial" means in the context of a POS display isn't immediately clear. Is it RS232, RS232-like or something more complicated, bi-directional perhaps ?

You seem to know some of the spec - Do you have a manual which gives any further information, how it connects to something else, etc ? What does the connector look like, PS/2, 9-way D ?

I'd expect ( but could be wrong ) that IBM POS displays would all be compatible with each other, VFD, LCD or whatever so any IBM POS reference may prove useful. You could also open the unit and start tracing signals from the connector to see where they go, that should reveal the physical interface side of things.

I've thought about the use of POS displays because they are usually large and well built, but my concern has always been what protocols they use. I suspect it's unlikely they simply display whatever is sent to them but will need some initialisation sequence or use a more complicated proprietary protocol simply to lock people into using the same equipment. Then there's a security aspect; preventing the insertion of a 'black box' which shows a customer a total $1 higher than the till will take. Never got my hands on one to try.

The most useless bit of proprietary kit I ever got was an ICL VDU. BNC in for video, BNC out for keyboard. It output a video field with 'pixels set' indicating which keys were held down. All the intelligence was in banks of video drivers / keyboard decoders installed in the mainframe rack :-(

 

[springer]

thanks for the help...

after carefully re-checking my work i found a small metal trace had shorted the +12v (required by the vfd) to one of the picaxe pins... so i'm down 2 * 18x's, but not disheartened!!
I've also discovered that one of the displays is also known as a wd-202a from digipos... so manuals galore!
another display is marked as a m202md15b, and unknown go google! this has a fixed baud / data type (i'm assuming 9600/8/n/1), so only displays (repeatable) garbage when connected to an 8m, but that's all i have left to test it with until i get a fresh delivery of 18x's.
(And now to buzz out the pins on a non standard lcd touch screen module, there's enough to be parallel, but who knows ;-)

 

[hippy]

another display is marked as a m202md15b, and unknown go google! this has a fixed baud / data type (i'm assuming 9600/8/n/1), so only displays (repeatable) garbage when connected to an 8m, but that's all i have left to test it with until i get a fresh delivery of 18x's.

For 9600 from an 08M you can take serial from Output Pin 0, SETFREQ M8, then use SERTXD to transmit - That will be the equivalent of SEROUT 0, N9600, ...

 

[springer]

thanks for that, according to the manual, only x parts are capable of 9600!!
Still getting garbage though!!!, I'll wait till i get a pic with more serial output variables.

 

[Andrew Cowan]

Hippy is talking about SERTXD, not SEROUT. This is for communicating to a PC at 4800 (normally), so overclock to 8MHz, and it will be 9600 baud.

It is fixed on the serial out pin - output 0 on an 08M.

A