I’ve installed a DOT HAT on my Pi and while the LEDs and backlights are working perfectly, I can’t get it to display text from Python. Nothing happens when I call lcd.write(“Hello World”) nor do any of the sample programs work.
I’ve tried all the suggestions here and elsewhere, have upgraded the OS to the latest version and even tried a clean re-install. I’m stuck!
Some background information: it’s a brand new Pi 2, running the latest Raspian. Nothing else connected at the moment except a wifi aerial. Power supply is 2.1A which I believe is sufficient. I installed the software using the curl script and also installed WiringPi as suggested elsewhere, and made sure boot/config.txt had the spi line.
Only one other thing I can think of: I have also been running a PiLite on this Raspberry Pi although I obviously don’t run both at the same time.
Before I send it back as a faulty unit (I’m not sure I believe that’s the problem) have I missed anything else out? All help gratefully received!
Which examples are you running, and what library are you importing to write to the LCD? Could you post a snippet of your code.
Sure. I’ve tried all the examples which are supposed to display something and none of them work. Essentially it’s this:
import dot3k.lcd as lcd
lcd.write(“Hello world”)
Nothing happens on the DOT HAT. It’s definitely working otherwise, because I can control the backlight and LEDs.
Can you try:
import dothat.lcd as lcd
lcd.write("Hello World")
If it works, I’ll be in the other room, kicking myself.
Still nothing happens, I’m afraid. Don’t start kicking yourself just yet :-)
Drat. Is this Python 2 or 3? I’ve go to get to the bottom of this- I’m certain there’s something amiss in the software but it’s hard to track down.
$ python --version
Python 2.7.3
Happy to help you track down the problem if you let me know what else to look out for.
Thank you. I’ve had it happen to me once and was certain I’d fixed it.
Let’s try working around the software:
import dothat.lcd as lcd
import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setup(12, GPIO.OUT)
GPIO.output(12, GPIO.HIGH)
time.sleep(1)
lcd.write("Hello World")
This will no-doubt spit out some warnings, but hopefully…
Nope still nothing. No warnings either though.
Actually it should probably be:
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(12, GPIO.OUT)
GPIO.output(12, GPIO.HIGH)
import dothat.lcd as lcd
lcd.write("Hello World")
But also try:
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(8, GPIO.OUT)
GPIO.output(8, GPIO.HIGH)
import dothat.lcd as lcd
lcd.write("Hello World")
Still no joy. But after the statement “GPIO.setup(8, GPIO.OUT)” I get the following error:
main:1: RuntimeWarning: This channel is already in use, continuing anyway. Use GPIO.setwarnings(False) to disable warnings.
Note: I think I’m on to something with the latter. I’ve been cross referencing my library code with the schematics and think I’ve overlooked the Chip Select pin. Previously I thought the Reset pin was at fault- but reset has a 10k pullup on it. Chip Select does not! Although looking at the datasheet Chip Select is active low, so that latter code should probably be:
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(8, GPIO.OUT)
GPIO.output(8, GPIO.LOW)
import dothat.lcd as lcd
lcd.write("Hello World")
Still quiet, same warning. Here’s the full output:
$ sudo python
Python 2.7.3 (default, Mar 18 2014, 05:13:23)
[GCC 4.6.3] on linux2
Type “help”, “copyright”, “credits” or “license” for more information.
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(8, GPIO.OUT)
main:1: RuntimeWarning: This channel is already in use, continuing anyway. Use GPIO.setwarnings(False) to disable warnings.
GPIO.output(8, GPIO.LOW)import dothat.lcd as lcd
lcd.write(“Hello World”)
Drat! I think we’ll have to try a replacement and retrieve yours for some testing in-house. I can’t shake the ominous feeling that I’m in for a colossal facepalm moment in the near future.
Could you drop us an email to support with your order particulars, please?
Thanks very much for bearing with me, I still can’t shake the feeling it’s something to do with the software.
It really doesn’t help that I don’t have a DOTHAT with me tonight to actually tinker with!
Sure, no problem. I’ll sort it out tomorrow. I’m with you - I suspect it’s a software problem too. The HAT seems to be working fine otherwise. Thanks for your help!
Out of curiosity, what does the soldering look like on all the pins that join the screen onto the main HAT board? I’ll upgrade you so you can post a photo if you’ve got the time!
Ok, here’s a photo. It looks ok to me but I’m no expert! I’ll send it off today.
Looks pretty much spot on to me too! If it doesn’t miraculously work when we get it back to test ( which is some sort of law of the universe or something )- it’ll be scope time!
Ok I will send it back to you. What should I include with the parcel? Do I need a returns number or anything or are you not that bureaucratic?