HC-05/HC-06 Bluetooth Module

[Peter Ellens]

I'm just a little concerned

Looking at the wiring diagram you have the 5v Nano connected directly the the 3.3v RX lines of the HC-05, which are not 5v tolerant and only rated for 3.3v
The TX is fine as the Nano will interpret 3.3v from the HC-05 as a high signal.

Unless you have a voltage divider in there thats not documented.,,

Or perhaps you have used modified HC-05  for 5v eg http://www.instructables.com/id/Make-Bluetooth-HC-05-Module-5v-Compatable/

Please advise

Thanks



 



 

[Steve Pendergrast]

Hello,

Although some models of HC05 are not 5v tolerant, many of them are specifically designed to be usable with 5v Arduino these days. The ones we use are marked E475833 and the manufacturer's own documentation shows direct hookup of Rx to a 5v Uno digital io pin in their "example circuits" section of their user guide.  I found the module schematic and there is a setup on the module to make it 5v tolerant. (It's not a voltage divider, it's a diode and a pullup resistor arranged such that if input is high the pullup kicks in because the diode blocks the +5v coming from the input pin, and if input is low the diode allows the input to pull the Rx pin on the actual bluetooth chip low.  This is a very common way to get 5v tolerance without using a voltage divider. A divider will waste some current all the time so is undesirable in a battery driven application).

Trust me, I've used hundreds of these modules with no dividers, some for years at a time, and I have never once lost a module hooked up this way.

I think I should probably make a note on the electrical diagram page that the electrical system requires a 5v tolerant HC05 because you are not the only person who has pointed this out!  There are many tutorials on the internet that show the divider always being used. It's necessary for some HC05 models but not others.

Hope this clarifies things!

[Eric Albert]

In the paired set I received in the kit I saw one with a red dot on the label.  Is this the master or slave?  And does it matter which goes in the gamepad/robot?  I didn't see any mention of that in the build instructions.  My modules pair but don't communicate yet so I need to check the wiring at least...

[Steve Pendergrast]

In about the first 50 kits we shipped we used the red dot to indicate MASTER.  After that we got a little smarter and marked them "M" and "S" instead.

Although it does not currently make any difference which is the master and which is the slave, we do plan on having an app in the future, and in that case you'd need the slave to be in the robot and the master in the gamepad for the app to work.

I'm taking a look at our documentation to clarify this. The decision to go forward with an app was fairly recent, just the last couple of weeks.

[Eric Albert]

OK, thanks!  I made the red dot association as "R"  for "robot" thus I'll switch them for the future app use.  I suspect I've got a TX/RX reversal at one end or the other which is easy to check.

[Steve Pendergrast]

It's pretty darn easy to mix up Tx and Rx. I did it wrong half  the time on about the first 10 I built LOL.