<![CDATA[LoPy and custom PCB with L76-L GPS module]]>We're trying to implement custom PCB with the same module as used in PyTrack - Quectel L76-L.
This question might be a bit off topic but is it necessary to use level shifter to talk to this GPS module through I2C bus ?
We perform i2c.scan() and getting no response from connected and powered module while UART interface works perfectly.

Are LoPy I2C bus levels compatible with L76-L ?

]]>https://forum.pycom.io/topic/2723/lopy-and-custom-pcb-with-l76-l-gps-moduleRSS for NodeWed, 22 Apr 2026 17:45:14 GMTMon, 26 Feb 2018 14:08:57 GMT60<![CDATA[Reply to LoPy and custom PCB with L76-L GPS module on Mon, 26 Feb 2018 14:08:57 GMT]]>We're trying to implement custom PCB with the same module as used in PyTrack - Quectel L76-L.
This question might be a bit off topic but is it necessary to use level shifter to talk to this GPS module through I2C bus ?
We perform i2c.scan() and getting no response from connected and powered module while UART interface works perfectly.

Are LoPy I2C bus levels compatible with L76-L ?

]]>https://forum.pycom.io/post/16347https://forum.pycom.io/post/16347Mon, 26 Feb 2018 14:08:57 GMT<![CDATA[Reply to LoPy and custom PCB with L76-L GPS module on Mon, 26 Feb 2018 14:32:04 GMT]]>@bobie

Is the device a 5v or 3.3v device? If it is 5v you will need to use a level shifter. Do you have pull up resistors for the SDA and SCL lines?

]]>https://forum.pycom.io/post/16353https://forum.pycom.io/post/16353Mon, 26 Feb 2018 14:32:04 GMT<![CDATA[Reply to LoPy and custom PCB with L76-L GPS module on Mon, 26 Feb 2018 14:51:58 GMT]]>@seb We use LoPy4 so "device" is 3.3V I believe. Quectel says:
...

  • I2C_SDA/I2C_SCL is pulled up to 2.8V inside L76-L module. There is no need to add a pull-up resistor externally.
  • The voltage threshold of I2C is 2.8V. If the system voltage is not consistent with it, a level shifter circuit must be used.

Quectel I2C voltage characteristics:
VILmin=-0.3V
VILmax=0.7V
VIHmin=2.1V
VIHmax= 3.1V
VOLmax=0.42V
VOHmin=2.4V
VOHnom=2.8V

]]>https://forum.pycom.io/post/16360https://forum.pycom.io/post/16360Mon, 26 Feb 2018 14:51:58 GMT<![CDATA[Reply to LoPy and custom PCB with L76-L GPS module on Mon, 26 Feb 2018 15:07:37 GMT]]>@bobie

Out modules output 3.3v which is above the maximum 3.1V specified there, to be safe I would include level shifters. Simple bi-directional level shifters can be made like so:

0_1519657652355_1366896b-6981-4748-b469-be068e05c5cb-image.png http://husstechlabs.com/wp-content/uploads/2010/09/Level-shifter.jpg

]]>https://forum.pycom.io/post/16363https://forum.pycom.io/post/16363Mon, 26 Feb 2018 15:07:37 GMT<![CDATA[Reply to LoPy and custom PCB with L76-L GPS module on Mon, 26 Feb 2018 15:19:48 GMT]]>@seb OK, will try to use level shifter. Do Pycom use level shifter on its PyTrack module ?

]]>https://forum.pycom.io/post/16366https://forum.pycom.io/post/16366Mon, 26 Feb 2018 15:19:48 GMT<![CDATA[Reply to LoPy and custom PCB with L76-L GPS module on Mon, 26 Feb 2018 15:27:08 GMT]]>I just checked the Pytrack schematic and we use the i2c interface to the module and actually don't have level shifters, that must mean it works ok.

]]>https://forum.pycom.io/post/16368https://forum.pycom.io/post/16368Mon, 26 Feb 2018 15:27:08 GMT<![CDATA[Reply to LoPy and custom PCB with L76-L GPS module on Mon, 26 Feb 2018 15:46:07 GMT]]>@seb We connected our Quectel L76-L pins:

L76-L .................. LoPy
GND------------------------ GND
VccInput ----------------- 3.3V VccOut
SDA ------------------------ P9
SCL ------------------------ P10

Then we initiated:
i2c = I2C(0, I2C.MASTER)
i2c.init(I2C.MASTER)
i2c.scan()

On our L76-L i2c.scan() produces empty array and multiple execution produces sometimes random adresses.

When we connected PyTrack PCB using only those 4 pins the L76-L from PyTrack gives proper response to i2c.scan()

What I did wrong ;-( ?

]]>https://forum.pycom.io/post/16371https://forum.pycom.io/post/16371Mon, 26 Feb 2018 15:46:07 GMT<![CDATA[Reply to LoPy and custom PCB with L76-L GPS module on Mon, 26 Feb 2018 16:19:04 GMT]]>@bobie It still looks like wrong signals. If you can do so, hook up an oscilloscope and check the signal quality.

]]>https://forum.pycom.io/post/16372https://forum.pycom.io/post/16372Mon, 26 Feb 2018 16:19:04 GMT<![CDATA[Reply to LoPy and custom PCB with L76-L GPS module on Mon, 26 Feb 2018 16:36:00 GMT]]>@bobie

Do you have pullup resistors on the SDA and SCL lines? You will need to connect a 10k resistor between those lines and 3.3V. It's also worth noting that on the Pytrack the I2C is sda='P22', scl='P21'.

]]>https://forum.pycom.io/post/16373https://forum.pycom.io/post/16373Mon, 26 Feb 2018 16:36:00 GMT<![CDATA[Reply to LoPy and custom PCB with L76-L GPS module on Tue, 27 Feb 2018 17:25:06 GMT]]>@seb No luck with pull up resistors. There is also garbage when connected on P22/P21.
PyTrack connected to the same pins with the same settings goes smooth.
While connecting our L76-L there is no response on I2C ;-( only garbage response for i2c.scan().

Maybe you reconfigure L76-L chip through UART after mounting ?

Will try to connect oscilloscope and/or logic analyzer

]]>https://forum.pycom.io/post/16417https://forum.pycom.io/post/16417Tue, 27 Feb 2018 17:25:06 GMT