On Fri, 17 Jul 2020 18:37:09 +0200, "R.Wieser" 
declaimed the following:

>
>The problem is the HC-05 module /doesn't/ run on 5v - ever.  Its also a CMOS
>device.  Both of which Alister seems to have overlooked.
>

 The actual module (the sub-board soldered to the break-out) is 3.3V...

 But that one on Amazon whose schematic I keep referencing has a
transistor cascade (shown just below that diode) which seems to use
UART_TXD (from the module) to the first transistor to pull down a 3.3V
pull-up feeding the second transistor, and that second appears to be used
to pull down a 5V pull-up on the "TX_TTL" output.

 So... back to oscilloscope on the TX and ground, and hope the device
defaults to High (otherwise you'll need to send something to it and get it
to echo back). A DVM might show the High voltage level IF that is the idle
state, but won't react fast enough to show the peak of an actual data
signal (the o'scope will).


--
 Wulfraed                 Dennis Lee Bieber         AF6VN
 wlfraed@ix.netcom.com    http://wlfraed.microdiversity.freeddns.org/

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