HC-05 module on a JY-MCU breakout board - what and how is it buffered ?

TNP,

As you said, the origional TTL spec - for the classic 74xx series.

And thats just how the those chips interpreted /incoming/ signals. /Outgoing/ signals where ofcourse safely quite below and above it. A logic "high" for them is defined as /at minimum/ 2.4v (under heavy load), with no upper limit.

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.

Regards, Rudy Wieser

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

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/

Dennis,

I wonder about that. The PDF I got here mentions "1.8V low-power operation, 1.8 to 3.6V I/O". Its possible that the 3.3v supply voltage is only needed when the I/O should be 3.3v ...

The module I have has only a single three-legger (the other one I mistakingly mentioned is a two-legger, probably a diode - one side very close to VCC), and is probably the voltage regulator. So, no way something active happens with any of the signal lines.

Thats a bit of a problem with the output lines : no way to "wiggle" it a bit by using breakout board pins and see which HC-05 module "pin" moves with it. :-\

I thought of something, and attached my scope to the DMV in resistance measuring mode. What-do-you-know, only in the two lowest positions (diode test and 200 ohm) the voltage over the probes is 3v. As soon as I switch to

2K ohm the voltage drops to 250 mili-volt. Not enough to hurt anything. Putting a 1K resistor over it drops the voltage to below 100 mili-volt.

IOW, it looks like we've (or at least I've) been carefull for no particular reason. :-)

Don't like to have to cut away the transparent heatschrink tube protecting the module though ... I do not even have heatshrink tube of that size laying about, transparent or not.

Regards, Rudy Wieser

I have over looked nothing, simply did a quick search on the device & found more than enough information to understand the device you seem to be up to your usual trick of either completely failing to understand or deliberately trying to complicate the situation.

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3.3V...

device

Idle on an Asynchronous serial interface is defined as a 1 which is +V

so a simple meter should suffice in this case.

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Alister,

... but are still dumb enough to suggest we should just connect a 3.3v devices inputs to a 5v devices outputs.

Kiddo, you already lost (my interest) when you posted your "Tx & RX are described as TTL serial TTL is a fully detailed standard as far as signal levels go." response, with

*zero* actual response to the parent, my post.

Face it kid, you /claim/ its all obvious to you, yet you cannot seem to answer any of my questions.

Regards, Rudy Wieser

Alister,

Goodness. You have the RS232 "zero" and "one" correct ! As for the "TTL serial", I already posted a link to that. Repeating it doesn't score you any points.

Also correct. Than again, nowerdays that info is rather easy to google.

Obviously you have not even read my question. That or you now realize that you have no clue to how to answer it, and are trying to throw sand in my/everybodies eyes. 'Cause what I asked can't be determined by "a simple meter" (why did you think I asked in the first place?). You fail again.

You have accused me of "you seem to be up to your usual trick of either completely failing to understand or deliberately trying to complicate the situation.". I'm now accusing you from either deliberatily trolling, or being much less knowledgable than you think you are (but not prepared to admit it to anyone, possibly including yourself).

Regardless, you have earned yourself a place ito my (non PC) blacklist. Goodbye.

Regards, Rudy Wieser

as I used to design industrial equipment that comunictaed using many diferent serial protocols (RS232, 20ma Current loop & even the IBK Keyboard interface) I think I can Justifiably state that I know it at least as well as you & probably better.

look at who made the post I responded to. Dennis suggested you actually try to check the output physicaly if you were unsure but was not certain a meter would suffice. I was clarifying things for HIM.

I cite your posting history as evidence. I'm now accusing you from either deliberatily

Pot - Kettle or being much less knowledgable than you think you are (but

Thank you, I guess I will do likewise in case I am foolishly tempted to help in future

--
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   -- From a Slashdot.org post

Oh yes. Good decision.

I know,but that is not what is at issue. Those chips are NOT TTL, although they are guaranteed to work with ttl level signals, so they do not *redefine* the TTL spec.

You can, but not many people bother

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..I'd spend it on drink. 

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