HC-05 not working as intended with Arduino Uno

Hello!

I'm trying to use an HC-05 with an Arduino Uno but I can't seem to connect with my PC via Bluetooth. When I plug in the 9V battery on the Arduino, he HC-05 turns on and starts to blink rapidly and continuously, followed by no lights and a small blink, followed by rapid blinking again. Acording to this link: http://www.martyncurrey.com/arduino-with-hc-05-bluetooth-module-in-slave-mode/ I'd say the module pairs with the PC but then returns to the mode where it is waiting for a pairing.

The connecions between the Arduino and the module are: Arduino - Module GND -> GND 5V -> Vcc Tx -> Rx

Whenever I start this, the Tx light on the arduino never blinks.

The code is very simple and it is just meant for testing:

void setup() { Serial.begin(9600);

}

void loop() { Serial.write("Hello");

}

Whenever the arduino is connected to the PC, this works as intended.

Any suggestion on what to test here?

Any suggestion on what to test here?

Test using a real power supply. The bluetooth device is a power-hungry device. A 9V battery, the rectangular PP3 type, is suitable for a smoke detector, not powering an Arduino and an bluetooth module.

PaulS: Test using a real power supply. The bluetooth device is a power-hungry device. A 9V battery, the rectangular PP3 type, is suitable for a smoke detector, not powering an Arduino and an bluetooth module.

My idea would be to use this as a portable device. What should I use then? Any other sort of battery?

What should I use then?

Shouldn't you get it working, first?

Any other sort of battery?

I use 4 AA batteries to power my Arduinos with XBees. Should work for you, too.

PaulS: Shouldn't you get it working, first? I use 4 AA batteries to power my Arduinos with XBees. Should work for you, too.

Well, I should, but it has no use for me if I'm not able to make it portable.

4 AA batteries wouldn't supply less power than a 9V battery?

HC-05 modules are 3.3V devices, and can be destroyed by connecting the 5V TX to the HC-05 RX.

Check yours to see if it has level shifters on the serial lines (most cheap ones DO NOT).

If not, you MUST use a level shifter, at least for TX(Arduino) to RX(HC-05). See this forum post and this one too.

jremington: HC-05 modules are 3.3V devices, and can be destroyed by connecting the 5V TX to the HC-05 RX.

Check yours to see if it has level shifters on the serial lines (most cheap ones DO NOT).

If not, you MUST use a level shifter, at least for TX(Arduino) to RX(HC-05). See this forum post and this one too.

That might have happened so I need to check it. In the event of the module being destroyed that way, wouldn't it even start? Or would it have an erratic behaviour?

It could be that only serial port pins are affected, leading to the appearance of erratic behavior.

Try another module, they are very cheap. Be sure to use at least the minimum level shifter, 1K and 2K resistors between TX (Arduino) and RX (module).

4 AA batteries wouldn't supply less power than a 9V battery?

4 AA batteries will supply [u]far more power[/u] than a 9V block battery. Block batteries are almost useless for Arduinos.

4 AA batteries will supply far more power than a 9V block battery. Block batteries are almost useless for Arduinos.

The 4 AAs will supply less voltage but more current than the 9V battery.

Reviving this thread because I believe there’s no need to create a new one.

I was off for some time and picked this up again today. Disconnected the Tx/Rx to check how the module would be answering to the power suplly from the PC and if I could rule the connection module/PC out. I haven’t been able to buy the batteries and the support yet.

When I connect the arduino to the PC the module starts blinking rapidly. If I check the device manager of my PC I see that the bluetooth devices are paired. After around one minute of blinking rapidly, the blinking stops, the lights blink twice and on the device manager I see the devices are connected. After this the rapid blinking returns and it all repeats.

Is this a normal behaviour for the module? I belive the power provided by the PC should be enough for it to work decently, so I’m not really sure on what to think of this result

HugoTorres: Is this a normal behaviour for the module?

Not really. I guess you have the HC-05 on a ZS-040 breakout board. This gives a quick double flash at about two second intervals after a connection is made but, once made, the connection should stay connected until disconnected. While it is reasonable to expect that the power from a PC would be adequate, the repeat cycle you describe suggests it isn't. Maybe the problem is slack wiring rather than an actual shortage of power.

"Paired devices" is barely relevant. "Pairing" simply means getting on the dance card, something you may have done last week. Connecting is what you want to know about, which is done by the terminal programme or w.h.y, on the PC.