How to access serial console port using openwrt wifi router (serial to wifi)

Installing and Using OpenWrt
#1

I just bought GL inet, in order to be used for accesing some equipment that using DB9 serial port. I'm wondering instead of connect using wire from my laptop to corresponding device through serial port, I want to use my mini wifi router to be used as converter for serial to wifi, so I can access device with serial console interface wireless. Please explain it with the simplest method

Regards,
Siti

#2

The RS232 port will fry most any router instantly. They can run up to +/-15 V and potentially peak at +/-25 V. Even the 5 V levels of "TTL" can permanently damage a router.

You need a USB-to-serial adapter (or level shifter) with 3.3 V logic levels to connect to the internal serial on the router.

If you need to connect from the router to "RS232" equipment, then determine if it is compatible with TTL levels, or if you need true RS232 with its +/- signaling. An appropriate USB-to-serial adapter with a DB9 male, then either a null-modem adapter or null-modem cable should do the trick. You'll need to install the USB drivers from the OpenWrt packages (or GL.iNet repo, if using their OEM firmware).

https://openwrt.org/packages/table/start?dataflt[Name_pkg-dependencies*~]=usb-serial

1 Like
#3

Wouldn't it make more sense to use a Pi or the likes of these SoC boards that are intended for that purpose (provided the voltage will not be an issue, as those also work with low voltage), and will allow installing a "bigger" Linux distro that can be useful for whatever you want to achieve.

#4

None of the SoCs typically used can drive RS232 levels, or even TTL levels into an RS232 load. RS232 signals +/- 15 V, though some receivers are compatible with TTL levels. Some SoCs don't even run 3.3 V logic, but may be at 2.4-2.7 V.

The AR300M and a dongle is a fine way to get "wireless serial" -- well-built, compact, low power, and not very expensive. I almost bought a handful of AR300M-Lite units for that kind of thing.

#5

Like mhegab says... my kit here would lend itself to ESP(32 or 8826) and MAX232 ttl to rs232 ( possible buck step down for them too )....

MAX232 ttl to rs232 are handy... as are premade level shifters....

But unless you have to have the smallest package or other GPIO benefits... I think Jeffs option is much better.

1 Like
#6

Thumbs up on the MAX232 and its later-generation devices (from various manufacturers) if you're into soldering and getting really tiny, lightweight, and/or low power.

Other GL.iNet devices to consider might be the GL-MT300-V2 (~US$20) or the VIXMINI (~US$17). I don't have any experience with MTK, so I can't comment on the chipset in those, though each of the three GL.iNet models that I do own I find to be well engineered with very good build quality, reliable, and well supported by a communicative, responsive manufacturer.

If you want to go really DIY, I've been playing with the Nordic Semi nRF52840 Bluetooth 5 (with "LE" capabilities) as an eval board the size of a USB key for US$10 (Mouser, US) -- pair that with an RS232 level-shifter and...

KEY FEATURES

  • 64 MHz Arm® Cortex-M4 with FPU
  • 1 MB Flash + 256 KB RAM
  • Bluetooth 5 multiprotocol radio
  • 2 Mbps
  • CSA #2
  • Advertising Extensions
  • Long Range
  • +8 dBm TX power
  • -95 dBm sensitivity
  • 4.8 mA in TX (0 dBm)
  • 4.6 mA in RX (1 Mbps)
  • Integrated balun with 50 Ω single-ended output
  • IEEE 802.15.4 radio support
  • Thread
  • Zigbee
  • 1.7-5.5 V supply voltage range
  • Full-speed 12 Mbps USB
  • NFC-A tag
  • Arm CryptoCell CC310 security subsystem
  • QSPI/SPI/TWI/I²S/PDM/QDEC
  • High speed 32 MHz SPI
  • Quad SPI interface 32 MHz
  • EasyDMA for all digital interfaces
  • 12-bit 200 ksps ADC
  • 128 bit AES/ECB/CCM/AAR co-processor
  • On-chip DC-DC buck converter
  • Regulated supply for external components up to 25 mA
#7

Or just get a USB to Serial Adapter that ranges within the 3.3 volt range.