Problem with multiple 7 segment displays & raspberry pi

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latteier
 
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Problem with multiple 7 segment displays & raspberry pi

Post by latteier »

Hi,

I'm trying to get these items working:

1 x Raspberry Pi Model B 512MB RAM[ID:998]
2 x Adafruit 1.2" 4-Digit 7-Segment Display w/I2C Backpack - Red[ID:1270]
1 x Adafruit Assembled Pi Cobbler Breakout + Cable for Raspberry Pi[ID:914]
1 x 4-channel I2C-safe Bi-directional Logic Level Converter (BSS138)[ID:757]

I can get the pi to control one of the 7-segment displays or the other, but when I attach both at the same time it doesn't work, and neither device is detected.

Here's one display:

Code: Select all

$ sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: 70 -- -- -- -- -- -- -- 
Here's the other (which I have set to address 71)

Code: Select all

sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- 71 -- -- -- -- -- --
When I use the python library I can control either device when it is the only one attached, but I get errors when I connect both devices at one.

I am using the logic level converter (hopefully correctly) to convert the I2C signals to 5V for the 7 segment displays.

I guess it's possible that I've wired the 7-segment displays to the through the level converter incorrectly. I've attached the pi's 3.3v, ground, SDA, and SCL pins the low side. I've wired the pi's 5.0v, and ground and the device's +, -, D, and C pins to the high side of the converter.

Thanks for any suggestions!

-Amos

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adafruit_support_bill
 
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Re: Problem with multiple 7 segment displays & raspberry pi

Post by adafruit_support_bill »

Please post photos showing your soldering and connections to both of the displays.

latteier
 
Posts: 5
Joined: Mon Apr 21, 2014 4:24 pm

Re: Problem with multiple 7 segment displays & raspberry pi

Post by latteier »

I've attached an ugly drawing of the circuit.

Thanks for your help!

-Amos
Attachments
circuit
circuit
circuit.jpg (533.78 KiB) Viewed 595 times

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adafruit_support_bill
 
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Re: Problem with multiple 7 segment displays & raspberry pi

Post by adafruit_support_bill »

A photo would be better. We need to see the soldering too.

latteier
 
Posts: 5
Joined: Mon Apr 21, 2014 4:24 pm

Re: Problem with multiple 7 segment displays & raspberry pi

Post by latteier »

Here are some photos.

It's pretty hard to see anything since I don't have a macro lens.

You may notice that I soldered the headers on the level shifter upside down. :-(

Thanks again for your offer to help!

-Amos
Attachments
DSC_9072.jpg
DSC_9072.jpg (166.21 KiB) Viewed 586 times
DSC_9071.jpg
DSC_9071.jpg (117.6 KiB) Viewed 586 times
DSC_9069.jpg
DSC_9069.jpg (147.49 KiB) Viewed 586 times

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adafruit_support_bill
 
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Re: Problem with multiple 7 segment displays & raspberry pi

Post by adafruit_support_bill »

Try it without the level shifter. Connect the pin marked "IO" to 3.3v, then you can connect the SDA and SCL pins direct to the cobbler.

https://learn.adafruit.com/adafruit-led ... t-backpack
For use with 3.3v processors, connect the IO pin to 3.3v. This will keep the I2C bus signals at a safe level for your processor.

latteier
 
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Re: Problem with multiple 7 segment displays & raspberry pi

Post by latteier »

Thanks for your suggestion of powering the displays with 3v3.

It worked. Except that the displays were *very* dim. I cannot read them in indoor light. This won't work for my application.

I am trying to follow the instructions here:

https://learn.adafruit.com/matrix-7-seg ... rything-up

That page suggests powering the displays with 5v, but using a level shifter to control them via 3v3.

I'd like to be able to achieve that, if it's possible.

-Amos

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Re: Problem with multiple 7 segment displays & raspberry pi

Post by adafruit_support_bill »

Thanks for your suggestion of powering the displays with 3v3.
That is not what I suggested. I said to connect the "IO" pin to 3.3v. This sets the voltage for the 2c bus. The "+" pin is what provides power and must be 5v.

Please follow the wiring instructions in this tutorial: https://learn.adafruit.com/adafruit-led ... t-backpack
Now you are ready to wire it to your microcontroller. The required connections are:
"D" - I2C Data Pin (SDA)
"C" - I2C Clock Pin (SCL)
"+" - 5v. (Will not run on 3.3v!)
"-" - GND
"IO" - I2C bus voltage.

latteier
 
Posts: 5
Joined: Mon Apr 21, 2014 4:24 pm

Re: Problem with multiple 7 segment displays & raspberry pi

Post by latteier »

Yes. Thank you very much it's now working!

I appreciate your patient help!

-Amos

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