On Wed, 15 Jul 2020 22:53:14 +0200, "R.Wieser" 
declaimed the following:

>- Which pin of the HC-05 module is it connected to ?  (presuming it is)
>- Is it a direct connection or does the break-out board have any components
>(resistor, diode, etc) in it.  If the latter, for what purpose (what is its
>effect).

 The odds are very good that all pins on the module map directly to the
same pin of the HC-05 chip itself... And most likely the chip specification
sheet will use the same name.

 Now -- if they are buffered/inverted between the module pins and chip
should be in the documentation from the module manufacturer. If there is no
such documentation, or only a reference to the chip specification, it is up
to you to determine what is happening or contact the module manufacturer.
(Let me guess, you went lowest bid on eBay for this)

https://www.instructables.com/id/Success-Using-the-JY-MCU-linvor-Bluetooth-Modu
le/
https://www.tautvidas.com/blog/2015/12/easy-arduino-bluetooth-communication-wit
h-jy-mcu/
(Note: this particular variant indicates the "Key" [EN] pin is used to
update the on-board firmware and not to toggle into AT command mode --
might be a difference between HC-06 and HC-05 chips; feel free to search
for spec sheets of the two for comparison)

https://www.instructables.com/community/Are-the-JY-MCU-and-the-HC-05-bluetooth-
module-the-/
implies the module has voltage converters for 5V I/O.

https://www.amazon.com/Master-Slave-Anti-Reverse-Integrated-Bluetooth-Pass-Thro
ugh/dp/B07JFYSZR6#detail-bullets
The schematic diagram shows a Maxim MAX3232 chip -- but it appears that
chip is unused unless you wire up to some of the pads on the module. The
MAX3232 is used to translate TTL UART signals to real RS232 (+/- 12V). {The
J1 connector has both TTL level and RS232 level -- but that is on an 8-pin
connector, but the module only exposes a 6-pin connector} There is a
transistor cascade taking "UART TXD" and boosting it up to 5V "TX TTL"
level. "RX TTL" appears to just be fed to through a diode to drop the
signal to 3.3V "UART RXD". Note that both of those conflict with the bottom
labeling on this module, which states 3.3V levels for RXD and TXD.

 At this point, I'd probably pull out an oscilloscope and put that on
the output pin&ground, then apply first 3.3V to the module, followed by 5V
-- and seeing what voltage peak appears on the output (the schematic
implies the output has a 5V pull-up, so I'd guess that is the default level
for the output, and the transistors are used to draw it down to GND level).


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

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