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HC-05 Master / Slave Bluetooth Module (HCMODU0061) 
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Joined: Thu Nov 05, 2015 10:44 am
Posts: 1
Post Re: HC-05 Master / Slave Bluetooth Module (HCMODU0061)
I have finally achieved getting two HC-05's master/slave talking to one another via two Arduinos (i.e one hc-05 connected to one arduino wirelessly tx/rxing chars to the other arduino). I have discovered that not all the info on the web has been accurate but definitely helped.

Main differences with my setup:
The "en" pin on the hc-05 has absolutely no affect on obtaining AT Command mode. Apply power, press the button, remove power then reapply power gets the thing into AT Command mode. The baud rate is always 38400 in AT mode.
That said - "AT+INIT" does not return "ok" it bombs out of AT mode.
You have to +Link<slave addr>, +bind<slave addr>, and something else on the master. I found it was the link cmd that returned "ok". The others returned error(16) but I persevered..... The master/slave pswrd have to be the same. Then after an init.... the led status changed to intermittent double blink. Hurrah!
No swapping tx/rx was required....... that was a red herring.......
Also the default baud rate obtained by the +uart cmd has to be checked. Make sure that is set up correctly. That is the baud rate of the wireless connection - not the AT mode connection. I set mine up to 38400,1,0 and it worked!


Thu Nov 05, 2015 11:15 am
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Joined: Fri Jul 08, 2016 8:06 pm
Posts: 1
Post Re: HC-05 Master / Slave Bluetooth Module (HCMODU0061)
On other forums I've seen it suggested that the HC-05 RX pin (data in) cannot be connected directly to an Arduino because the voltage must be reduced to 3.3v. Is this true of the module sold by Hobby Components?


Mon Nov 14, 2016 10:23 pm
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Joined: Sun Aug 05, 2012 4:15 pm
Posts: 620
Post Re: HC-05 Master / Slave Bluetooth Module (HCMODU0061)
Yes that is correct. It's not 5V tolerant so it shouldn't be directly connected to the digital output of a 5V Arduino board. You'll need to level shift the signal. The easiest way to do this would be to simply use a couple of resistors as a potential divider.

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Tue Nov 15, 2016 9:54 am
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