I am having problem with getting your HC-05 modules into AT mode. The module I got does not have a push button. I have already followed the tutorial provided but it’s still not working. My wiring are as follow,
Vcc - 5V
En - pin 9 of Arduino
Gnd - Gnd
Tx - Rx of Arduino
Rx- Tx of Arduino
When I upload the code, I unplug the Vcc pin of HC-05 to make sure EN pin is HIGH before the module got power. After uploading, I reconnect the Vcc pin. Please let me know if there’s anything wrong with my settings and if there are any tricks to get into AT mode. Thanks!
Perhaps try some common baud rates for these Chinese modules. Common bauds include 1200 / 9600 / 38400. Let me know how you get on.
I have tried in both 9600 and 38400 baud rates. Still not working. I notice there’s another guy in the forum having the same problem as I do. He mentioned that he could get into AT mode for the ones with button but not for the ones without button. If it’s hard to find the reason for this, I would like to order a HC-05 module with button since I am on a project with very tight schedule. Is it possible?
Sam is back in on Monday, we’ll grab one off shelf and give it a whirl and will let you know how we get on. Stay tuned for more.
I’ve used both HC-05 a bit before and created a tutorial on the process. I tested the process with both the button versions, and the wire versions and it held up for both. One trick I noticed is that you have to be careful with when you connect the EN pin in regards to the power cycle of the Arduino. Take a look at the tutorial here (which includes step by step examples and code) and let us know how you go.
Thank you for your help. I have tried following the tutorial and for some
reason I still cannot get into AT mode and LED is still flashing rapidly. I
have tried in different baud rates and different styles of wiring. Still no
luck. If possible, I would like to give it a try with the HC-05 module with
button. Is it possible to order the specific module with button?
Thanks for your help again!
Unfortunately, the modules are a lucky dip as far as whether they have a button or not, however, the baud rate of communication doesn’t have any impact on getting it into AT mode. The only requirement to put it into AT mode is the EN pin being held high at power up. Try following the exact method I outline below, and if it doesn’t work, we can go down the replacement route.
Unplug Arduino from your computer/power
Disconnect all wiring from the Arduino to the HC-05 except for GND and 5V
Connect the EN pin to 5V while the module is still powered off
Connect power to the Arduino
Does it enter into AT mode after those steps?
I followed your instruction exactly, but the LED is still flashing rapidly.
I’ve attached the wiring of my arduino and HC-05. Please let me know if
there is any problem with the wiring. I powered on the arduino only after
connecting the EN pin to 5V. I also checked with multimeter to make sure 5V
is flowing into Vcc and EN pin.
I note you grabbed two - are they both doing the same thing?
If so, that’s incredibly unusual and we’ll grab a couple out to test on our side to figure out why these steps are not working.
Yes. I grabbed two of those and both of them are having the same problem.
Ok thanks for that. It’s more than likely that our tutorial needs to be updated if you’re running into the issue with two boards. We’ll check it out step by step tomorrow and will report back in the morning.
So I grabbed a HC-05 and got it on the bench and discovered that the breakout board for it is indeed the version that is supposed to have a button on it (as it has an ‘EN’ pin not a ‘KEY’ pin). so it seems that an odd batch either have the button missing or are just a one-off irregularity. Either way, it’s fairly easy to get it up and running. I’ve modified the tutorial that I linked you to with instructions on how to enter into AT mode without the button.
Long story short, the EN pin (as with those that have a button) is useless, so you’ll need to either solder a wire to pin 34, or solder two wires to the button jumper pads (if you wish to use an external button rather than a microcontroller pin).
For more detailed info, take a look at the updated tutorial. Hope that helps!
Also, you mentioned that you were using 5V on the EN pin? Note that the HC-05 is a 3.3V device. It has a 5V regulator on board so you can power it with 5V, but only ever send 3.3V to it, and you’ll need a logic level converter between it and your Arduino to use it. Only give it 3.3V to pull-up the KEY pin.
Thanks for your help. I soldered pin 34 to 3.3V and the module finally got into AT mode. Apart from the AT mode problem, I want to know if it’s possible for one HC-05 Master mode Bluetooth to be connected to multiple slave devices at the same time?
Glad to hear it got sorted out. You can definitely connect a single Bluetooth Master to multiple Bluetooth Slave devices. In the Introduction to Bluetooth tutorial, it talks about those type of connections which are known as piconets.