RTC options for E20C / E52C?

#1

Hi,

I was wondering if there are any options to populate the HYM8563TS RTC on E20C/E52C. I’m really thinking about replacing my aging devices with combinations of these ones which, from now, are the best match for my use case, but given that upon power outage, my machines boot in roughly 20s while the ISP’s box takes 5 minutes, there’s no way to restart at the correct time for a while, and RTC solves this.

I’ve looked at the pads on the E52C, I feel like I could handle soldering the RTC controller itself, but the 0201 resistors are too small to just maintain them in place during soldering, especially the pull-up ones which are very close to each other. Also, finding a flat xtal is not trivial, the ones I’m having are a bit thick. Thus I’d rather pay one extra buck to have them on board!

E52C is available now
#2

Hi willy

You can populate the HYM8563TS RTC on the E52C while following the RTC related circuitry on the schematic.

What is your confusion?

#3

I’m speaking about having it soldered on the board by default. My board doesn’t have it, and the components are too small for me to risk doing it (the chip should be OK but not the 0201 pull-up resistors). I have no problem with the schematic, that’s where I figured where it was supposed to be :wink: (U17 IIRC).

#4

Sure, let’s just solder it by default. It’s not soldered because the network switch usually doesn’t have RTC builtin. But we are smart network device, we should have it.

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#5

Ah, many thanks for this @hipboi . I’ll be interested in knowing when it’s safe to order new devices with the chip in them. I’ll happily order a new E52C to replace the current one, as well as a few E20C for my low-power proxies.

#6

FWIW I finally managed to rebuild such a tiny module by salvaging some components from an old RK3288 HDMI dongle. I’ve added a 0.33F supercap, a diode for the charge, and two 6k8 pull ups, and connected it to the HYM8563’s SCL/SDA pads (which fortunately are directly connected to the bus), and to the 3.3V capacitor behind the SD card’s connector. I had trouble getting it to be recognized by the driver (it said it had corrupted data) but it turns out that I “just” needed to clear the “VL” (voltage low) bit in reg addr 2 using i2cset and rebind the driver. At this point it was properly recognized and at least it didn’t lose the power during the time it took me to better resolder the wires and reassemble everything. 10 years ago I successfully used a 0.47F capacitor on an ALIX board and it would last about 20 days, so I think I’ll have at least as long. I’ll see. I’m adding two photos of the assembly (I used shrink tube to protect the connectors and forgot to take a photo before that).

IMG_0552_cs
IMG_0552_cs.JPG1600×1200 152 KB
IMG_0544_cs
IMG_0544_cs.JPG1600×1200 155 KB

So the conclusion is:

  • it’s possible to connect an I2C slave to those pads provided you add your own pull-up resistors, which should make it possible to use more accessible devices such as DS3231. Still you’ll need a 0.2mm soldering iron tip and a magnifier to avoid creating shorts between the pads.
  • there’s quite some room over the SD connector which is about as tall as the RJ45 connectors and larger than the SD connector, suitable for a tiny CR1220 or supercap plus a small board.
  • thin enough wires (I used wrapping colored wire) have no problem passing between the PCB and enclosure to place the device on the top despite the chip being at the bottom.
  • there are plenty of RTC boards on aliexpress, I’ll see if the DS3231 I ordered can fit once I desolder the connector.
#7

For those interested in adding their own RTC themselves, I managed to make another such module, and it’s definitely doable for a somewhat trained individual. I’ve documented all the steps there with accessible and affordable components. Be prepared to spend at least half a day on it, though: