Here's a quick post showing how I solved an issue with an unreliable LTE backup connection. Depending on your hardware, firmware & UI version YMMV.

The problem

It appears that Huawei E3372 frequently disconnects from the LTE network for no apparent reason. It wouldn't be much of a problem if it managed to quickly and reliably reconnect, but that isn't the case it would seem. Whenever that happens packets get lost and websites don't load properly, and overall internet experience is well below acceptable. After some googling it turned out that it might be caused by E3372 automatically disconnecting from the network, but fortunately enough, automatic disconnects when idling seem to be a configurable feature [sic] in the HiLink version of the modem. Less fortunately though, the default interval is set to 5 minutes, and obviously needs to be changed, potentially even disabled altogether. Let's see what the WebUI has to offer in this regard:

Oh...

After a lengthy break I'm back to the UPNOD series. This time we'll take a closer look at the dynamic random-access memory (DRAM) circuitry present on the PCB:

As usual, all of my findings can be found here.

A second installment in the UPNOD series, this time we'll take a look into the reset circuitry of the telco card.

As the title implies, this circuit is responsible for generating a proper Z80' reset sequence. Z80, being a rather dumb piece of clever electronics, may boot up in an undesirable undefined state and requires a few cycles of special treatment to properly initialize internal register values. This circuit does just that - it generates the initial reset pulse and handles reset signals coming from other parts of the board, all while maintaining proper synchronization.

Since my last actual post on this blog I have acquired a new class of hobbies - electronics. Most recently, reverse engineering of really old computers. This series of posts will be about a vintage eighties TelCo computer-card-thing marked UPNOD CARD0117 TN64 I bought on a local auction:

All my findings will be posted on this blog and the accompanying data will be gathered in this GitHub repository.