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General project discussion / help
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By mtmtntop
#197914
i have a sparkfun serial 16x2 lcd (https://www.sparkfun.com/products/9066) that reads data from a light sensitive resistor . I also have a 2 channel relay that operated based on a value of the same resistor. the sketch for both of these items work on my arduino uno. I was having trouble with the relay itself, which is powered by a wall wart 5 v power supply. I came across this post in the arduino forum.
https://forum.arduino.cc/index.php?topic=185234.0
which included a great diagram how to wire the relay to isolate the power sources. Once i wired according to this diagram all was well with the relay. ( Removed jumper between VCC and JVCC, and wall wart + to JDVCC, wall wart - to grnd. Relay module powered from arduino 5v to relay VCC and grnd )
However, now my lcd , which had been working, is garbled and changes garbled characters every minute as the loop of the sketch runs.

The I found this , again in the arduino forum:

https://forum.arduino.cc/index.php?topic=327960.0

In this thread, one of the suggestions that seemed to work was:

LarryD suggests adding filtering on the LCD power pins.. This means soldering a 10µF capacitor (with the correct polarity) between pins 1 and 2 of the display board itself. People have found these displays surprisingly sensitive to power fluctuations.
It seemed this was the correct forum to ask as its a sparkfun lcd. I have 2 questions. Will this solution work for this lcd ?
The documentations shows pin 1 as ground and pin 2 as 5v.
and second, I looked at the board to find pins 1 and 2 and find that they are not marked. It seems pins 1 and 2 depend on which side you are looking from. Which pins are 1 and 2? Thanks for your help.
By paulvha
#197919
Have the LCD down facing on the table. You see the small board on the back with the blue connection points 5V/ GND/ RX to the right.
On that small board top left : JP2 ( 6 pins) , the middle 5 are not used, then JP1. (6 pins)

TOP left (next to JP5 on the LCD board): First pin 1 is GND, pin 2 is SECOND left 5V.

Watch try to keep your wires that connect away from the relays or try to shield them. Make sure your power supply is strong enough. Another capacitor could
also be connected on the Arduino 5V.