New 'labman' tool

Wolfgang Denk wd at
Sun Apr 19 22:17:24 CEST 2020

Dear Simon,

In message <CAPnjgZ04mLcNzbJJYzK9g_W+j0KB9ge5mYjpyDmqhe7rgCcO4g at> you wrote:
> I have been fiddling with setting up a lab and have found it quite a
> pain. Lots of USB connections and things sometimes break.
> Hubs are a pain because their internal numbering does not always
> correspond to their visible port numbers.
> Also when something goes wrong with a component in the lab, it is hard
> to know which one is broken and which port it is on.

This is a repeating story, and my strong recommendation is just to
get rid of USB devices as much as possible.

Where exactly do you need USB stuff?

- TTL to serial converters - there is a wide range of (usually
  MAX3232 based) TTL to RS232 converters; which you can then connect
  to some standard terminal server (aka console server).

  There is also TTL to WiFi adapters, though not exactly cheap, for
  example [1]

  A DIY approach could use some ESP8266 based system - you get a
  Mini NodeMCU for as little as $0.10 today [2]; adapting the free
  tasmota firmware to work as serial converter is easy.

- Power switching - again, there is a large number of ESP8266 based
  wifi plugs that can run Tasmota; I prefer the Tuya compatible
  ones, because you can flash the Tasmota firmare OTA without any
  physical manipulation [3], and they are relatively cheap ($8.95
  per plug, for example [4]). If in doubt, use standard Sonoff

- Relays (boot mode switches etc.) - for example the Sonoff 4CH Pro
  R2 offers 4 relays, and again it can be flashed to run Tasmota,

  Alternatively, just use a ESP8266 NodeMCU and a Transistor (and
  maybe a relay).

You get the pattern?  Most of these things can easily be replaced
with devices that can be controlled over WiFi (using for example
MQTT over TLS), using Free Software only.  You can access averything
over the same mechanism, and you don't need to route so many cables
aby more. USB maximum cable length?  Forget it.  USB hubs? Forget

SCNR - I'm aware that all this is pretty off topic here.


Best regards,

Wolfgang Denk

DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at
Anyone who isn't confused here doesn't really know what's going on.

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