Samsung 20M102DA1 VFD assistance?

Castigo · Post by **Castigo** » June 19th, 2006, 10:53 am

Hello all ive just retrieved one of these samsung VFDs from where i work and i am keen to use it in an upcoming project.

Ive managed to get the VFD to work with smartie...unfortunately the character map is out of whack ie if i type a X it comes out as a 1 and not an x.

Ive checked the parity is on non parity and the speed is correct, in previous occaisons when ive worked with VFDs it was a matter of getting the speed right and thats all.

Can anyone give me any suggestions or for those of you who have a bit of programming expertise any ideas on how i can remedy the problem, it would be much appreciated.

cheers

Post by **mattcro** » June 19th, 2006, 12:16 pm

I guess you're using the serial port? Is the problem just that the characters are wrong, or does it not respond correctly to any commands? The serial input on the VFD might be TTL levels rather than RS232, in which case you probably need a level-shifter along the lines of the MAX232 or the single-transistor circuit in several serial-backpack schematics.

Castigo · Post by **Castigo** » June 19th, 2006, 5:05 pm

Argh i did forget to mention, yes im using the serial port at 19200 bps, the serial port is putting out around 5-6volts on the pins.. if that helps?

Post by **mattcro** » June 20th, 2006, 10:01 pm

Are you getting any sensible response from the display? Does it actually respond to commands like "clear display"?

A quick Google shows up some info on that display that suggests the serial interface is TTL, not RS232 (they use different voltages and the signal polarity is inverted). This means that you will need a RS232 to TTL converter.

Is that 5-6volts with the display connected? That's a bit low for a serial port (except maybe a laptop), so the display input might be clamping the signal to TTL levels (0v and 5v).

The converter can be very simple - see X7JAY7X's serial LCD project for a schematic. You can use almost any small NPN transistor and diode.

Matt.

Castigo · Post by **Castigo** » June 20th, 2006, 11:52 pm

Cheers for that mate, ill give that a go

_X7JAY7X_ · Post by **_X7JAY7X_** » June 21st, 2006, 4:04 am

More may be going on than TTL conversion. I did a quick check of ASCII. X-> 0101 1000 x-> 0111 1000 1-> 0011 0001

They are not inverted but weird things happen if bits are inverted. It will throw off the start and stop bits of data. To see if inverting is going on you would have to look at a string of data.

I have to agree with Mattcro, I would try a MAX232 or equivalent first.

J