On Fri, 17 Jul 2020 13:45:55 -0400, Dennis Lee Bieber wrote:

> 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).

Idle on an Asynchronous serial interface is defined as a 1 which is +V
for a ttl serial or -V for RS232 (RS232 is  defined as ±3 to ±15 nots
imply ±12 as often quoted)
so a simple meter should suffice in this case.



--
There is very little future in being right when your boss is wrong.

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