Imp going to sleep causes write to LCD

Squirrel Code
#1

Since I have added deep sleep to the programming for my thermocouple temperature monitor, I noticed an extra gibberish character at the end of the second line on a 16x2 LCD. After some research, It appears that when the Imp goes to sleep, something happens that “writes” the character. The character doesn’t appear if I use imp.wakeup() instead of deep sleeping to schedule the repeated temperature reads.

Any suggestions on this? I tried reconfiguring Pin 8 before sleeping, but I still get the character. Will I need to fix this on the hardware side?

This does NOT happen on the Adafruit RGB LCD (serial backpack) that I have, only on the Sparkfun LCDs.

#2

You’ll need a pull up (or down, I don’t know what the idle state is) resistor on pin 8 to ensure that the line stays in a “safe” state when the imp stops driving it.

#3

Thanks Hugo, I had a feeling that was the answer. If I measure the idle voltage of the the pin, will I be able to tell which way to pull it?

#4

It looks like the idle state is HIGH, so I put a 10K resistor between Pin 8, and 3.3V. No more goofy characters! Thanks again.