I have made an underglow project for my car and first did all my programming and testing on a 10amp 5v power supply. Everything worked fine and no problems came up. Now that I have wired everything up, 12v from the battery is passing through a 20 amp inline fuse then through a toggle switch and then to a 5v 30amp converter. This then powers the LEDs and the Arduino, the Arduino is powered through a USB cable that is attached to the 5v 30 amp circuit but the HC-05 module is connected straight to the Arduino which is on and has its LED's on. every time I toggle on and off the circuit, once I toggle it back on, the Arduino powers up but not the HC-05 Module> The only temporary fix I have found for now is to unplug either power to the HC-05 or the ground and plug them straight back in their spots. I am really confused and have looked at many problems this module has had running on 9v lipo batteries but none have helped. will include a picture in future posts if needed.
Thanks for the help,
Paul
PaulIsFrench:
the Arduino powers up but not the HC-05 Module> The only temporary fix I have found for now is to unplug either power to the HC-05 or the ground and plug them straight back in their spots.
If you know that Arduino is OK but Bluetooth isn't, then clearly either
- There is no power connection from Arduino to Bluetooth
- Bluetooth is a dud.
Your second sentence is incoherent but if you are saying that you can get power to Bluetooth OK, then it isn't a dud, and option 1 applies. All those amps to hand suggests that you have adequate power, but I would keep the LiPos out of the game. In short, the evidence suggests you have slack-arsed wiring.
PaulIsFrench:
has had running on 9v lipo batteries
9V LiPos, what type of LiPos are those ?
No, I am running the whole system off the car 12v battery, I just searched through forums and found that there was problems with the modual not powering up on 9v probably alkaline batteries
The problem is the Arduino is on and running off the system, the Hc-05 module is plugged straight into the 5v out of the Arduino, but it doesn't turn on when power is turned on to the whole system and the Arduino is on, I have to manually unplug just the HC-05 and plug it back in so wiring is out of the question. It also worked fine before I put it on the car. I'm going to try to add a relay with a delay to turn it on will update you when I have done that.
PaulIsFrench:
The problem is the Arduino is on and running off the system, the Hc-05 module is plugged straight into the 5v out of the Arduino, but it doesn't turn on when power is turned on to the whole system and the Arduino is on
IF you are using HC-05 on a standard breakout board like a ZS-040, powering it off the 5v point of Arduino is normal practice. What you need to know is why this won't work for you when it does work for everybody else. I therefore suggest you read reply #1 at least twice before you go off on some other tangent.
wiring is out of the question
Your evidence suggest it is very much in the question. You might also note that "wiring" is a loose term that includes sockets, and availability of adequate power.
Running Arduino of a 9v alkaline is a seriously bad idea, unless you really know what you are doing, and what the limitations are.
I'm going to try to add a relay with a delay to turn it on
Messing about with a delay and relays is likely to just move the problem rather than fix it and, even if it does work, it probably won't for long and is definitely not something that you should show you mother.
Ok but why would it work at all if the wiring was bad, literally all the connections are all soldered, crimped and heat shrinked. The Arduino powers on, which means there is 5v power going to the Arduino, and the HC-05 runs directly off of it, I have tried moving/adding grounds.
PaulIsFrench:
Ok but why would it work at all if the wiring was bad,
As I understand it, not all the wiring is bad, and Arduino works fine all the time every time, but it only takes one bit of wiring to be bad - quite likely something that has been crimped, soldered, and heatshrinked, but not very well. I guess the first bit of proof is done by leaning a voltmeter against Bluetooth Vcc while it is trying to run, rather than just talking about it.
Seriously, if you have a wiring problem but Arduino is OK, this can't be hard to sort out. Right now, your biggest problem is admitting that you have stuffed something up. You will be amazed how often people do that, and the something is probably very small..
Well no because I checked, and there is power going to the module, I just don't know why it won't turn on, it has the right amount of power, and it has a good ground. I have resistors where they are needed. I am really flustered, I would admit if my wiring was faulty. But I have already checked, and when the power and ground from the Arduino are going straight into the module and there is power and ground but the thing doesn't turn on, I don't understand why.
I really do appreciate you trying to help me out though, so thank you for your ideas. I am going to continue to try and fix it and will get back to you if you think of something else, or if I figure it out. 
I've had dry joints on my HC-05.
Hello guys,
anyone found a solution yet? I'm facing the same problem, c. f. here: Bluetooth modules for Arduino - Project Guidance - Arduino Forum
I'm currently thinking it must be something with the speed of voltage rise or fall on the VCC pin. Have you tried your idea with the relay? That's exactly the kind of workaround (given that the behaviour of the HC05 is as I suppose) that just came to my mind: Using some kind of fast switch (transistor, MOSFET, relay...) that is off at the beginning and then gets turned on after a delay (or by the Arduino itself when it's running). Would be nice to know if that worked for you?
Greets
Hello
same here. My HC-05 needs reset after being powered with a LM2596 Buck Converter at 5V. Both Arduino and HC get power from the LM2596 but even if i power HC alone it doesn't power up.
I too believe that it has to do with delay of the regulator to reach voltage. Tried a cap but to no avail.
I was thinking there might be a reset pin somewhere on hc-05 so with a pull up it might work.
I guess your suspicions can't be hard to verify. Try running Arduino off a normal power supply with HC-05 connected in the normal manner. If that works, you know where the problem lies. There is a reset pin on HC-05. I have never heard of anybody needing to use it, and I'm not sure there is any point in you trying to be the first.
Ok the problem IS the power supply.
I added a switch to the circuit and suddently everything works. That is if i power first the supply and then the circuit.
If i leave switch on and turn the ps on then hc won't work.
By using a multimeter i can see that voltage from the ps isn't going straight to 5v but follows a curve. Event the arduino pwr led lights up slowly. Probably hc-05 doesn't like that and won't power on (for reasons beyond my comprehension).
By using the switch after powering the ps i supply 5v "instantly" to everything so hc powers happily on.
In my case i leave it at this as i am building a Neopixel strip, and the switch was part of the circuit. But for the rest i.e. the OP i think there still exists some mystery.