HC05 not discoverable

hey I am working on a 2 wheel balancing robot and I plan to control that using bluetooth via HC05 module now the problem is HC05 module turns on but it is not discoverable by either my phone or laptop. I have double checked my wiring and added and removed resistors etc but nothing seem to work any help will make things a lot easier for me :slight_smile: Thanks.

I have double checked my wiring and added and removed resistors etc but nothing seem to work

For this exercise, the sole purpose of the Arduino is to provide power - only power and ground wires needed, and the only thing that counts is the only thing you don't talk about - the LED.

If the LED is flashing at about 2Hz, it ready to connect. If it isn't, it isn't ready.

If it is flashing and you cannot connect, the problem is more likely to be at the other end and, in the case of the phone, is more likely to be procedural. I assume you are not talking about an iPhone but, even if you have made the mistake of using an iPhone, I believe you can still sniff an HC-05.

In the case of a laptop, the situation is more complicated by the bluetooth installation. You can still test this by having the laptop sniff for the phone, but I think it is better to stick with the phone for now.

If the LED is not flashing, it is time to check the wiring - again. You might then check that the voltage applied is as required. You do not mention if the HC-05 is a bare board or, more likely, on a backboard or even a shield. If it is on a backboard, it needs 5v. If it is on a shield, power is not likely to be a problem, unless you are using batteries.

Firstly thank you for replying. The led is flashing very rapidly when I power it up also it is getting the correct voltage of 5v from arduino also tried 3.3v same result. And no I am not using iPhone because hc05 apparently doesn't work with iPhones. Do I need to change any configuration settings ?

If the LED is flashing fast, it should be ready to connect. This may even be true if it is flashing with 3.3v, but don't bet on it. This should be true if you are using batteries, but the HC-05 is not famous for low power demand, so don't bet on that either. Use a proper wall wart or at least a USB cable to prove things.

You are right about the iPhone, but it may sniff it OK.

You do not need to change any configuration settings, there is nothing to change. Your problem is clear - HC-05 is not discoverable and, as I said Arduino is just there to provide convenient power. Discovery is a matter between Android and HC-05. All configuration is about communication between HC-05 and Arduino.

You need to be aware that there are two games being played

  1. Arduino talks to and listens to the serial port. It neither knows no cares that an HC-05 is connected to the port and totally oblivious about Android.

  2. Android talks and listens to HC-05 wirelessly. It neither knows nor cares that HC-05 is connected to Arduino by wires.

I would be reluctant to condemn HC-05 if the LED is flashing. I therefore submit your problem is at the Android end, and I assume it is just some silly procedural problem. I imagine you can disprove this by having Android discover the laptop.

You might find the following background notes useful


but I believe this is an Android problem