Inductive Charging and interaction with HC-06 Bluetooth Module

Dear Forum,

Good Sunday morning.

I am currently working on a project with:

I control the vibrator motor over Bluetooth using MIT App Inventor 2 (AI2). I use PWM and analogWrite from the Arduino Pro Mini to a transistor which in turn allows current to flow from the 3.7V power supply through the vibrator motor with flyback diode and then to ground.

The main issue that I am having is that the HC-06 loses power when the battery power dips below 3.6V, as it should, and then it CANNOT be restarted.

The Vcc for the HC-06 is 3.6 to 6V. When the Li-Ion battery is fully charged , it tops out at about 4.6V. So this should not be a problem for the HC-06. But when the voltage dips below 3.6V, there is not enough "juice" to supply the 3.3V on-board voltage regulator and the red LED on the HC-06 stops blinking. But even if I place the transmitting inductive charging coil over the receiving charging coil, I CANNOT GET THE HC-06 TO RESTART. It essentially goes dead. I have checked the voltage at the HC-06 voltage regulator and it is 3.3V even when the red LED has stopped blinking. But the Pro Mini stays remains illuminated.

I have swapped out HC-06 modules a couple of times. I have powered up the ones that I have removed using my benchtop power supply and they pair and connect.

The Seeed Studio inductive charging module charges up to 5V/1A. Does this charging coil have internal circuitry that will stop charging the battery once it achieves a full charge, even if it is under 5V?

How do I jumpstart the HC-06?

Please see the attached circuit diagram.

By the way, I have Arduino Vcc connected to Arduino PIN A0 so that I can monitor voltage. And I have HC-06 TX pin connected to Arduino PIN 8 (for AltSoftSerial) and I also connect this to PIN 2 as I was trying to use create an interrupt once the voltage level changed.


Dear Forum,

My previous message was posted after spending nearly 15 hours trying many things like:

  • swapping HC-06 modules
  • checking voltage levels at HC-06 voltage regulator
  • checking voltage level at HC-06 Vcc pin
  • resoldering connections
  • researching how to reset HC-06 (even though I did NOT alter baud rate, etc.)
  • researching how to repair HC-06
  • and going back and forth checking, double checking, triple checking, etc....

That being said, I NEVER use this forum as my initial path for solving problems. It is only after much careful thought and experimentation that I sit down and draft a carefully thought-out posting describing the problem with background information, etc.

So after my last posting, I went down to my shop. I thought that I might have an extra brand new Li-Ion battery in one of my bins of electronic components. And sure enough I did.

As I was pulling the battery wires away from my PCB so that I could place my soldering iron tip on the pad where the positive battery wire was soldered, so that I could remove the old 3.3V and ground wires from my PCB, the existing positive battery wire broke right off of the PCB. I was blown away how easily it just broke off. I soldered it right back on and this may have solved the entire problem that I have been having intermittently for literally weeks. I cannot tell you how many times I have checked the voltages all around with my DMM and then with my o'scope to monitor power and to look for erratic voltage levels.

I believe that the problem is now solved. I WILL NOT FALL VICTIM TO THIS UGLY SCENARIO EVER AGAIN (famous last words as I am laughing to myself and shaking my head simultaneously in disgust and in victory)


No, HC-06 is a 3.3v device. The breakout board is made for 3.6 > 6v, and uses on-board regulators, hence the 3.6v. You can get an HC-0x on a 3.3v board, and one that is switchable 3.3v or 5v. Another and, in your case perhaps better, option is to simply get a bare HC-05, no breakout board, and share the supply to same with that for the Pro Mini i.e. a properly regulated 3.3v.

Probably not such a good idea, and I note there is no comment on monitoring the mA, which is probably more to the point. Check your data sheets. If you wire up the supply to Bluetooth in the proper manner, you probably won't need to check anything. Needless to say, "proper manner" also means adequate supply. 850mAh sounds a bit mean, but maybe you are already abreast of that, and this is just an exercise in short-term portability.

Dear Nick,

Thank you for your reply. I overzealously stated 850mA for the battery. The battery is actually 400mA (Lithium Ion Battery - 400mAh - PRT-13851 - SparkFun Electronics). But I wanted the capacity to run the vibrator motor for longer durations anyway, so the higher capacity is not necessarily a bad thing.

An input pin on the Pro Mini will only sink so much current. So why can't I just connect Vcc to PIN A0? I don't understand electrically why this is a bad idea.

Also, are you suggesting using the 3.3V supply on the Pro Mini to provide power to the HC-06? Not really sure what you are suggesting.

The entire assembly worked great yesterday. The battery became depleted overnight and now I cannot "jumpstart" the HC-06 AGAIN!!!!! The HC-06 seems to go dead once the battery dies. I am not sure how to get this device back online even after I charge the battery back up.


You make your own decisions about batteries. All I can say is 850mA isn't much, and 400mA is less than half that. You make no mention of how long you expect this gear to run - or the power requirements of the peripherals.

All I am suggesting is that, if you use a bare 3.3v HC-05, you can use the same source to power it as you use to power a 3.3v Pro Mini. This may be either direct, or off Pro Mini's VCC pin. The bleeding obvious is that using a 3.6v breakout board with a 3.3v Pro Mini is a dumb idea, unless you have made proper provision to power it. This is simply a matter of using something that probably will work rather than hopefully might work, and you will not be the first to have a 3.6v board that fails when fed with 3.3v

Powering HC-05 off an Arduino signal pin can never be a good idea but using a signal pin to control a mosfet or w.h.y in order to control power supply to Bluetooth is common practice. HC-05 is not famous for its low power consumption, and I bet you haven't checked it, or how much power is available off pin A0. A Uno allows a max of 20mA and I don't suppose your Pro Mini is much different.

Jumpstart is an unknown term but I would have though there is no "seem" about HC-05 going dead when the battery dies, you should be able to bet your grandmother's pension on it. Further, there is nothing to suggest you won't have Bluetooth running in the proper manner as soon as you provide it with the proper power.

This may well be down more to luck than anything else, and your only problem is to introduce some certainty...

Dear Nick,

I am going to look into a bare 3.3V HC-05. Thank you. And the mosfett is a great idea. I will let you know how this works as soon as I receive the HC-05.


Dear Nick,

Is there a 3.3V variant of the HC-05? Or am I misunderstanding your suggestion? Vcc for every single HC-05 module that I see is 3.6V-6V.

ALL HC-05s are 3.3v, no ifs, no buts, no maybes, and no exceptions.
The 3.6 to 6v you see is the power requirement for the breakout board, with on-board regulator, that the HC-05 is soldered to. Even while this is the case, you might notice that the signal pins are still marked 3.3v.

It is possible to buy a bare HC-05, no breakout board, which requires a 3.3v supply, hence my comment in reply #2.

It is/was also possible to buy an HC-06 on a 3.3v breakout board, but it is not common, and I rather suspect about the only place it might be used is with a 3.3v pro Mini, or a close relative - also not common....

illustrations herein

Dear Nick,

I figured out how to make this circuit work MUCH better.

Previously, I had connected the Pro Mini RAW pin and the HC-06 Vcc pin both directly to the 3.7V Li-Ion battery. When the 3.7V Li-Ion battery was fully charged, it was somewhere around 4.4V if my memory serves me correctly.

The problem was that the HC-06 would power down at about 3.6V (Vcc for the HC-06 is 3.6V to 6.0V). So while the HC-06 would power down, the Pro Mini would still be running. This was not good.

I rewired a couple of things. First of all, I removed the power connection between the 3.7V Li-Ion battery and the Vcc pin on the HC-06.

Then I routed a wire from the Pro Mini Vcc pin to the Vout pin of the voltage regulator on the HC-06. Good reference at this link: . Go about half way down and it shows you how to identify the 3.3V regulator and which pin is Vout.

NOW both devices are running off of the same regulated voltage source. They work reliably and the connectivity is excellent.


No, that is the VCC for the board the HC-06 is soldered to. I believe some people actually get away with running that at 3.3v but it can't be a good idea - as I believe you are already aware...

Nonetheless, this all sounds very interesting, I think...

So, do I understand correctly that you used that article to make a conversion rather than the stated repair?. If so, it sounds like a better alternative than using a bare HC-05 module as I suggested - even if you don't already have a module on a breakout board ready to hand. I have published a child's guide to HC-0x Bluetooth, but I have no actual experience with 3.3v Arduino. It looks like what you have done will be a worthy addition to those notes.

Question: Could you not short out/remove/bypass the regulator, thereby enabling you to use the available Bluetooth VCC pin in the normal manner?

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