I have power supply, analog part and microcontroller part on one 2-layer PCB board, very simple. The LCD is on the microcontroller part. It works normally when I have it on a separate board with only the microcontroller, but when I put it in this board, the LCD only displays black dots, not text.

I have tried a few times but it still gives me the same result. I was wondering whether my PCB has any problems? Is it a grounding or decoupling issue? Or something else? Please take a look at my PCB and give me some advice.

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For more information, the power supply comes from a 7805 (on the Left Side of the Board). It drives a Cypress 27443 PSoC mcu, 1 INA126 Instrumentation Amplifier and 2 OPA4137 Op Amps. However I didn't put in the OPA when testing the LCD. The bottom part of the board is for the Amplifiers.

  • \$\begingroup\$ Need more information about the components, like what is the PSoC number, what is the application, what is OPA/7805 in the circuit etc... did you check the PCB track using a multi-meter for possible short circuit of LCD data lines etc. \$\endgroup\$ – Duresh Aug 3 '15 at 4:27
  • \$\begingroup\$ Thanks for your answer!I am using 27443 PSoC, the job of the uC is to convert ADC, provide DAC, reference voltage, some buttons and Rs-232 interface. The OPAs are used to process signal (in fact, it's a potentiostat circuit), they are on the lower side of the board, the left side is for power supply which I have separate grounds (don't know if that's properly grounded). I checked for the PCB track and they are fine, there are no short-traced \$\endgroup\$ – vuquan Aug 3 '15 at 4:34
  • \$\begingroup\$ What is the LCD that you are using? If it is Alphanumeric one, then your LCD wiring is wrong, else if you have an oscilloscope, check every data lines of the LCD for distorted pulses. \$\endgroup\$ – Duresh Aug 4 '15 at 2:06
  • \$\begingroup\$ Are your arrows pointing at curved traces (instead of 45°/mitred ones)? What makes that "bad practice?" See here \$\endgroup\$ – Shamtam Aug 4 '15 at 2:40
  • \$\begingroup\$ Are you complaining about curved traces? Why? There are so many things that are much worse, like all the acute trace joins. Sidenote: The component you are asking about is /probably/ a negative voltage regulator. \$\endgroup\$ – Connor Wolf Aug 4 '15 at 2:40

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