LCD display disappears

[Arul Raju]

Hello,

I'm working on a project to measure distance using ultrasonic sensor and Arduino Mega. I'm using 2 LCDs for output distance in mm. A separate 5V (1A or 2A) power supply unit is used for LCDs power supply.

The circuit uses 5V all over. The tower lamp connected to NO/NC contacts of 2 channel relay is 230V AC 50hz.
The LCDs are working fine when ultrasonic sensor gives initial sensing output, but after few seconds the LCD displays are blank (other functions are working fine as programmed). I have connected Arduino ground and 5V power supply ground in my circuit.I tried disconnecting tower lamp (230 V) from circuit, but displays are okay until i switch on any load (i.e room fan,light,heater). Not sure what is going on . There are no relation between relay output pins and the fans and tube lights.

The attached picture shows the pin numbers of LCD and respective supply voltage. Can you please help me fix this issue? Please let me know if you need any details.

 

[davenn]

The attached picture shows the pin numbers of LCD and respective supply voltage. Can you please help me fix this issue? Please let me know if you need any details.

the problem would appear to be in the circuitry that drives the LCD rather than the LCD itself
you be a good idea to show us the rest of the circuit as a schematic as well as a photo or 2 of your construction
maybe some one will see a wiring error

 

[kellys_eye]

The LCD contrast is set by the voltage on pin 3 and if this voltage varies (say under load) then you will see the display go off (or dark if it happened 'the other way').

Your description of circuit operation leads me to believe you haven't got decent enough regulation.

 

[Arul Raju]

the problem would appear to be in the circuitry that drives the LCD rather than the LCD itself
you be a good idea to show us the rest of the circuit as a schematic as well as a photo or 2 of your construction
maybe some one will see a wiring error

Here are the schematic and photographs of my project. Your help would be much appreciated as i have no clue on continuing this project.

Awaiting your earliest response. thank you so much in advance.

 

[Arul Raju]

The LCD contrast is set by the voltage on pin 3 and if this voltage varies (say under load) then you will see the display go off (or dark if it happened 'the other way').

Your description of circuit operation leads me to believe you haven't got decent enough regulation.

I use 10K potentiometer LCD brightness control. Please see attached schematic for more details. LCDs are working fine for few seconds and goes blank due to some other issue i believe. Thank you for your response. I appreciate it.

 

[kellys_eye]

You don't show the actual 5V power supply. What is its rating?

You really should add smoothing and decoupling capacitors on the power distribution board. Put a 1000μF in parallel with a 100nF capacitor on the 5V/GND board that the power is being distributed from.

 

[Arul Raju]

You don't show the actual 5V power supply. What is its rating?

You really should add smoothing and decoupling capacitors on the power distribution board. Put a 1000μF in parallel with a 100nF capacitor on the 5V/GND board that the power is being distributed from.

I'm not sure what is the rating of power supply. Can you advice how to find it out? Attached photo of power supply i use in my project. There is no spec sheet.

I will add decoupling as you suggested. Will it resolve the problem??

 

[kellys_eye]

If your PSU is under-rated then putting in smoothing/decoupling capacitors won't fix the issue. Your PSU should have details on it somewhere but you didn't add a picture (as your post said) so I'm clueless.....

 

[Arul Raju]

If your PSU is under-rated then putting in smoothing/decoupling capacitors won't fix the issue. Your PSU should have details on it somewhere but you didn't add a picture (as your post said) so I'm clueless.....

I bought new SMPS (5V, 3A output, Delta make) today. And connected capacitor in parallel as mentioned above. But still the problem is exist. The LCDs are gone when I switch ON room fan or during relay 1 and 2 changeovers. No idea what the issue is..Any suggestions please..Attached SMPS image.

 

[kellys_eye]

What is the TOTAL current consumption of all the devices and circuits?

 

[Arul Raju]

What is the TOTAL current consumption of all the devices and circuits?

I hope LCD draws (160mA), so 320mA +relay coil (30mA). That's all..

 

[kellys_eye]

When the display goes 'off' can you bring it back using the contrast control?

 

[Arul Raju]

When the display goes 'off' can you bring it back using the contrast control?

No, it is remain unchanged if I adjust potentiometer.

 

[kellys_eye]

Place decoupling capacitors (10nF and 10μF) close to the power pins of the active devices (displays etc).
Sounds as if there's some disruptive pulse getting fed into the display and making a reset condition happen (perhaps).

 

[Arul Raju]

Place decoupling capacitors (10nF and 10μF) close to the power pins of the active devices (displays etc).
Sounds as if there's some disruptive pulse getting fed into the display and making a reset condition happen (perhaps).

Sorry.. Iam back to this topic again after long gap. I have used capacitors close to power pins. But getting the same result, the LCDs are either disappears or filled with dark rectangle in shape.

I tried all possible ways to fix this issue, but no luck.

 

[kellys_eye]

Mount the contrast pot (change it to a preset) a LOT closer to the display panel - preferably directly on the pins of the edge connector. Having the contrast control on 'flying leads' and amongst that rat's nest of wiring can't be a good thing.

If that doesn't work, try using a new display.