After carefully assembling the LCD kit, then soldering the Blue 16x2 LCD to it, only the back-light works when connected to the Raspbarry Pi.
No characters are displayed.
Pushing the button next to Select lit the LED backlight, but no text was visible while running Adafruit_CharLCD.py.
There are no detectable shorts between adjacent pins.
After disconnecting and probing for continuity, and re-connecting to the rPi, the rPI won't boot. Something is seriously wrong, because if it is disconnected, the rPi LEDs immediately light and it boots.
How can this be debugged?
Could the MCP IO extender be bad?
All the contacts marked with a green arrow are connected (< 1 Ohm between them).
16x2 Blue LCD Kit for raspi
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Please be positive and constructive with your questions and comments.
- brent_1
- Posts: 5
- Joined: Fri Oct 11, 2013 7:41 pm
Re: 16x2 Blue LCD Kit for raspi
After rebooting the rPi, it's back to connecting again:
sudo i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
The PiPlate can be seen on the I2C bus (at addr 0x20), but only the LCD Backlight works.
1. cd Adafruit-Raspberry-Pi-Python-Code/Adafruit_CharLCDPlate
2. sudo python LCDtest.py
3. The backlight turns on and off, but NO characters are displayed
sudo i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
The PiPlate can be seen on the I2C bus (at addr 0x20), but only the LCD Backlight works.
1. cd Adafruit-Raspberry-Pi-Python-Code/Adafruit_CharLCDPlate
2. sudo python LCDtest.py
3. The backlight turns on and off, but NO characters are displayed
- brent_1
- Posts: 5
- Joined: Fri Oct 11, 2013 7:41 pm
Re: 16x2 Blue LCD Kit for raspi
The 4 connected pins on the MCP chip are A0, A1, A2, and #RESET.
Does it make sense that these would be tied together?
Who has a working board that they can disconnect from the rPi and test continuity on these pins?
Does it make sense that these would be tied together?
Who has a working board that they can disconnect from the rPi and test continuity on these pins?
- brent_1
- Posts: 5
- Joined: Fri Oct 11, 2013 7:41 pm
Re: 16x2 Blue LCD Kit for raspi
I got it working (for a while) by:
1. Unplugging the camera
2. Turning up the contrast all the way
It then worked for a few hours (using the Python library).
But overnight, it stopped working. And now the rPi won't boot while the LCDPlate it is attached.
Has anyone gotten this to work on a system that has the Camera enabled?
Any stability issues?
1. Unplugging the camera
2. Turning up the contrast all the way
It then worked for a few hours (using the Python library).
But overnight, it stopped working. And now the rPi won't boot while the LCDPlate it is attached.
Has anyone gotten this to work on a system that has the Camera enabled?
Any stability issues?
- adafruit_support_bill
- Posts: 88093
- Joined: Sat Feb 07, 2009 10:11 am
Re: 16x2 Blue LCD Kit for raspi
Yes. A0-A2 are the address pins and are all tied low by default. Based on the readings shown on the photo, the original issue was probably a simple contrast pot adjustment. Not sure about the possible camera interaction. Can you post a clearer shot of the soldering on the LCD display? Looks like there might be some issues there.The 4 connected pins on the MCP chip are A0, A1, A2, and #RESET.
Does it make sense that these would be tied together?
- brent_1
- Posts: 5
- Joined: Fri Oct 11, 2013 7:41 pm
Re: 16x2 Blue LCD Kit for raspi
I found the reason for the strange behavior:
The Up switch has < 1V on the high side - so it's always in the down state:
The other switches pull 5V down to 0, but the Up switch starts out at only 2V, then decreases, so at first, it works. But then after approx. 1 minute of being attached to a running rPi, it is always "on", given that it's voltage is now under the threshold (actual voltage is < .5V). That translates to a a LOW on GPA3. Which is interpreted as button Up *always* in the depressed state.
The LCD Connections, as requested:
What could be pulling the Up button supply down? (The other buttons are fine -- HIGH until pressed to pull them LOW). And why would it get worse as the board warms up (over 60 seconds, you can see the voltage level drop on the Oscilloscope.)?
The Up switch has < 1V on the high side - so it's always in the down state:
The other switches pull 5V down to 0, but the Up switch starts out at only 2V, then decreases, so at first, it works. But then after approx. 1 minute of being attached to a running rPi, it is always "on", given that it's voltage is now under the threshold (actual voltage is < .5V). That translates to a a LOW on GPA3. Which is interpreted as button Up *always* in the depressed state.
The LCD Connections, as requested:
What could be pulling the Up button supply down? (The other buttons are fine -- HIGH until pressed to pull them LOW). And why would it get worse as the board warms up (over 60 seconds, you can see the voltage level drop on the Oscilloscope.)?
- adafruit_support_bill
- Posts: 88093
- Joined: Sat Feb 07, 2009 10:11 am
Re: 16x2 Blue LCD Kit for raspi
I suppose it could be a bad switch, but the gradual decline sounds more like a bad pin on the MCP23017 port expander chip. If you contact [email protected] with a link to this thread, we can send you out a replacement.I found the reason for the strange behavior:
The Up switch has < 1V on the high side - so it's always in the down state:
...
the Up switch starts out at only 2V, then decreases, so at first, it works. But then after approx. 1 minute of being attached to a running rPi, it is always "on", given that it's voltage is now under the threshold (actual voltage is < .5V).
Hint: to remove the old chip, first clip all the legs off, then desolder them one-by-one.
Please be positive and constructive with your questions and comments.