My company purchased 55 Nova devices to deploy as part of a GPS tracking solution my company sells to school districts for school bus tracking.
The Nova has proven to work pretty well, but we have encountered a few problem areas:
the included antenna is not bad, but not great either. Many of our customers are rural and the LTE signals can be pretty weak. A more efficient antenna sometimes does the trick.
the Ublox module (SARA R410M-02B) itself includes some (imho) poor design decisions. The most significant is that only one communication channel is available when using the USB interface. I was using $5, 3G dongles which allowed two channels. With two channels, I can hand one over to ppp to manage data communications and use the other to query the device using AT commands to check connection status, etc. With the Ublox design, once I hand over the channel to ppp I cannot communicate with the Nova (unless I close the ppp connection).
To facilitate (1), we are adding an SMA connector to the device to accommodate more efficient antennas.
To address (2), we are adding a connector for access to the module’s UART. The UART interface allows, I believe, multiplexed access to the module so that even after a ppp connection is established, AT commands can be sent to the device.
Are there additional capabilities others in the community would like to see?
I would confirm (2) will work before you bother with the layout change, I think when USB is active UART is disabled, at least on the SARA-R410M:
See Section 1.9.1.1:
The UART is available only if the USB is not enabled as AT command / data communication interface: UART and USB cannot be concurrently used for this purpose.
Section 1.9.2.1
The USB interface is available as AT command / data communication interface only if an external valid USB VBUS supply voltage (5.0 V typical) is applied at the VUSB_DET input of the module since the switch-on of the module, and then held during normal operations. In this case, the UART will be not available
Presently, our plan is to expose the UART, no usb-to-uart converter.
It seems to me there are contexts in which a custom circuit board needs LTE connectivity and it may be more convenient/lower cost to connect via UART than USB.
Yes, the documentation is clear that the UART and USB interfaces cannot be used simultaneously.
With the current layout the 5V is sent to the Nova disabling UART, you will need to provide seperate 3.8V pads (to use without USB plugged in) or have some sort of switch to still use the 5V to ~4V converter from Hologram but remove 5V from the VUSB pin on the SARA.
Last suggestion is it may be worth putting a level shifter or atleast a 5V tolerant buffer between your UART connector and the SARA. I think its likely people will mess up and hook 3.3V or 5V logic up to the Nova UART pins accidentally.
I have been using the UBLOX SARA-R410M-02B-01 module and had a few questions.
Toggling between the UART and USB could be done with a single jumper on VUSB_DET pin such that the device could be powered from +1.8-5V?
In the system integration manual, Section 1.9.1.1 mentions that hardware flow control is not supported by this module. It specifically says RTS/DTR must set low.
Is there any reason or benefit to connect CTS, DSR, DCD, and RI with the R410M.
As a buffer will a bi-directional level translator can be utilized to handle ~2-5.5V input and V_INT logic level 1.8V. Something similar to figure 47 in 2.6.1.1.
The NOVA device uses a buck-boost switching power supply. Ublox specifically recommends using a LDO regulator for powering the module. Why was this type of power supply chosen and/or what is the advantage over a LDO? I assume that it was designed for being powered from batteries?
Personally I would put the flow controls lines in for a few reasons:
It may just be a firmware change to have them activated, so its possible in a future release to have flow control on SARA-R410-XX series
there is a new SARA-R5 series coming out that may have flow control enabled and its possible everyone will slowly migrate to this series
there are a lot of drop-in products in the SARA line, some of which do support flow control, you could use these chips with flow control without a layout change
You would need to put pull-downs on RTS/DTR or rely on a user to pull these down off board.
As for why Hologram went with an switching regulator I believe its because the board was orignally made for the SARA-G3 series which is 2G/3G and requires a 2A peak load during transmission. Since USB spec is only 500mA, you would be limited to only 500mA with an LDO but could get ~640mA using a switching regulator. Still under spec but less likely to brown-out.
The SARA-R4 series and pretty much all Cat-M1 devices spec a peak load of 500mA so this should be ok with an LDO on USB but without any margin.