Pull up error with soldered stemma cable

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fede2
 
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Pull up error with soldered stemma cable

Post by fede2 »

Need a bit of help here. I need to connect stemma stuff to a pybadge-lc and a pyportal. For neither I have the correct connectors or cables, so I snipped a cable in half and plan to connect each half to each board.

Not the best soldering, but I think the connections are ok. Now, when I connect any sensor over stemma, I get this Pull Up error in circuitPython. Not sure if SDA/SCL are in reverse or what I did wrong.
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stemma-pullup.png
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mikeysklar
 
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Re: Pull up error with soldered stemma cable

Post by mikeysklar »

Hello fede2,

Thanks for showing the pics of your code and i2c connection. All adafruit sensors on breakout boards including the DPS310 you are using have built-in pullups. The issue is either with wire length, soldering or wiring mixup.

Let's start with the logic pins. Make sure the DPS310 is connected to your pybadge-lc like so:

DPS310 <--> pybadge-lc
SCK <--> SCL
SDI <--> SDA
Vin <--> 3v/5v
GND <--> GND

https://cdn-learn.adafruit.com/assets/a ... 1556577492
Screen Shot 2020-04-02 at 9.04.34 AM.png
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fede2
 
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Re: Pull up error with soldered stemma cable

Post by fede2 »

I does look like it, I just check them with a multimeter with continuity from the soldered cable ends, to the pin holes of the sensor, and also measured voltage on the side of the sensor.
I'm adding a new crop of the original image, which shows that the cable I'm using is a normal stemma qt cable cut in half so it should not affect length wise.
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mikeysklar
 
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Re: Pull up error with soldered stemma cable

Post by mikeysklar »

Can you show the other end of the cable plugged into the sensor.

What was the voltage you were reading on each side of the sensor?

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fede2
 
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Re: Pull up error with soldered stemma cable

Post by fede2 »

Sure.
On the sensor side in the pin holes for vcc-gnd, it reads 4.18v when it's on battery, and 4.78v when the PyPortal plugged into usb.
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mikeysklar
 
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Re: Pull up error with soldered stemma cable

Post by mikeysklar »

You have the orientation right on the pins you have soldered to the PyBadge-LC

yellow SCK/SCL
blue SDI/SDA
red Vcc
black GND

Are you detecting any shorts in the connections when reading each pin with a mutli-meter. I'm more worried about the soldering than anything else. How much did you shorten the cable length when the JST connector was cut off?

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fede2
 
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Re: Pull up error with soldered stemma cable

Post by fede2 »

I cut the stemma qt cable in aprox half (so that I can use the other half on a poor pyportal that I'm going to have to remove the nice connector...).

I will try to re-do the soldering tonight and post a reply.

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fede2
 
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Re: Pull up error with soldered stemma cable

Post by fede2 »

I re-did the soldering, looks a bit cleaner, but I still get the same error.

Any ideas?
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mikeysklar
 
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Re: Pull up error with soldered stemma cable

Post by mikeysklar »

Hi fede2,

Thank for checking the solder points again. The blue SDI/SDA cable looks like it has a small connection the 5v trace. I circled it below.

The last time I had a killer troubleshooting issue the SDA/SCL error it turned out to be the i2c clock speed being set to high for the peripheral. I would suggest trying a lower clock speed as well to see if that helps.

Code: Select all

 i2c = busio.I2C(board.SCL, board.SDA, frequency=400000)
stemma.JPG
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fede2
 
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Re: Pull up error with soldered stemma cable

Post by fede2 »

I'm checking the solder with a jeweler's magnifying glass and it look ok.
If I can find the ccd for my microscope I'll take another image of it. It was probably a textile hair at the moment of the photograph.

I also added the code to change the speed of i2c but I still get the same error.

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fede2
 
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Re: Pull up error with soldered stemma cable

Post by fede2 »

Oh, I also check continuity with the multimeter, between the blue and red wire, and there isn't.

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mikeysklar
 
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Re: Pull up error with soldered stemma cable

Post by mikeysklar »

Okay, my bad on the baudrate. 400k is full normal speed. Let's drop you down to standard mode 100kbit/s.

Code: Select all

 i2c = busio.I2C(board.SCL, board.SDA, frequency=100000)

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fede2
 
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Re: Pull up error with soldered stemma cable

Post by fede2 »

Tested with the lower i2c freq, same pull up error.

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mikeysklar
 
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Re: Pull up error with soldered stemma cable

Post by mikeysklar »

Well aside from somehow have the SDA or SCL connections reversed (which I do not think is happening here) we might as well try the 4.7k pull up. Can you introduce a resistor on each of the SDA and SCL lines of 4.7k and see if it resolves the issue? This of couse should not be necessary, but it would be interesting to see.

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fede2
 
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Re: Pull up error with soldered stemma cable

Post by fede2 »

How would that go? From SDA I need to connect a 4.7k to GND or VCC?
And then the same with another 4.7k in SCL.

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