problem with LCD - analog and µc boards work separately only

[shreekalak]

problem with LCD

hi..
i am using analog and µc board separately.
i am giving my analog inputs to ADC of µc.
µc is interfaced with a LCD display.
Power supply to both boards is from different sources(transformers).
when i use both boards independently they work.
as soon as i connect both boards i.e. by giving the inputs to µc board and shorting bothe grounds my LCD shows up with boxes only..
after switching ON-OFF continuously my LCD shows output.
i am not able to find out the problem..
please help me soon..
its urgent...
thnx in advance

 

[cameo_2007]

problem with LCD

since there are two different transformers ,there could be a ground potential difference.
And another reason could be the noise from the analog board.

what you can check is by,
1. Make a single transformer as the supply source.
or,if you still need 2 tranformers,

2. Instead of shorting both the grounds together directly, short it through a ferrite bead or by a low value inductor,say 470nF

3.Provide a capacitor very close to the Vcc pin of display to ground ,preferably a 10uF aluminium electrolytic caps.

check this and tell.

-cheers

 

[shreekalak]

Re: problem with LCD

it seems problem of ground as i am using two transformers.
actually 1 transformer is used for generation of ±15V and other one is used for 5V generation which is used for µC board.
tranformer used in ±15V generation is center tapped while other one is not used in center tap config.
so can u please tel me wht shall do to make both these grounds at equal level.
cause i have not used such a config in which a center tap and normal transformer is used...
please help me soon
waiting for ur reply..

 

[cameo_2007]

problem with LCD

hwy not tap derive 5V also from the same +15V transformer using a regulator or something.

by the way did you check with the 2 and 3rd points i mantioned in previous post.?

Added after 1 seconds:

hwy not tap derive 5V also from the same +15V transformer using a regulator or something.

by the way did you check with the 2 and 3rd points i mantioned in previous post.?

 

[GrandAlf]

problem with LCD

Probably a much easier option is to use a single 5v psu or regulator, then get your +- 15v from a commercial switch mode psu block, direct conversion from 5v. These are commonly available, and inexpensive for low currents. Save yourself a load of trouble.

 

[shreekalak]

Re: problem with LCD

i got the solution..
now i have used the ground pin of three pin power plug connector as ground of all the circuit..
and the circuit starts working...
how important is the use of tht three pin plug ground in all the applications?
please let me know
thnks to cameo_2007 and GrandAlf....
thnks a lot...