Can't power HC-05. Please help!!

I am trying to use HC-05 (5V, onboard regulator levelling to 3.3v) with Arduino Pro Mini (3.3v) but I have had little success.

I am using a coin cell to power the pro mini which powers it on and is working fine.

But, my HC-05 doesn’t power on. I am trying to power it externally using two 3.7v Lipo-batteries that gives a total of 7.4v but I have tried numerous changes and nothing seems to work.

Circuit Diagram and HC-05 image attached below.

Please Help!!! :frowning:

The backboard probably states 3.6 - 6v quite clearly, thereby strongly implying that 3.7v is sufficient but 2x3.7 is probably too much. I don't suppose a coin cell has enough power to run an HC-05.

Nick_Pyner:
The backboard probably states 3.6 - 6v quite clearly, thereby strongly implying that 3.7v is sufficient but 2x3.7 is probably too much. I don't suppose a coin cell has enough power to run an HC-05.

The backboard says 5v. And it should support around 5~7v input.

I am only using the coin cell for powering the pro mini, and it works fine.

But what about the hc-05?

Depending on exactly which HC-05 you have the specification probably says something like 3.6V - 6V, over 7V prohibited.

And you're connecting 2 x Lipo cells to it, 7.4V nominal, 8.4V fully charged.

Can't you see any problem there?

Steve

slipstick:
Depending on exactly which HC-05 you have the specification probably says something like 3.6V - 6V, over 7V prohibited.

And you’re connecting 2 x Lipo cells to it, 7.4V nominal, 8.4V fully charged.

Can’t you see any problem there?

Steve

My HC-05 is 5v version with onboard regulator not the 3.6v-6v

hardik311095:
My HC-05 is 5v version with onboard regulator not the 3.6v-6v

So why does your circuit diagram imply your connecting 8.4V to a 5V input ?

srnet:
So why does your circuit diagram imply your connecting 8.4V to a 5V input ?

My battery is 3.7v rated so connecting one would not do the job for me that is why I connected two. Because I need 5v input voltage.

There are multiple other aspects to this project that is why I need these batteries. So, that I can extend my project further.

Does anyone seem to have an answer? please.

Which exact onboard regulator do you have? Many of the small regulators typically used on those breakout boards can’t handle >5-6V. Connecting two 3.7V batteries can easily kill them. Do check for the schematics/data sheet of your particular module, and check the limits for the on-board regulator.

What coin cell do you use that produces 3.3V rather than the common 3V?

hardik311095:
Circuit Diagram and HC-05 image attached below.
20908d804db3ba9044c5fc63e3b666bfa0c34e0a.jpg
172ff2998821069b14b989d14a60071abb715149.jpg

hardik311095:
My HC-05 is 5v version with onboard regulator not the 3.6v-6v

The chips on that board run at 3.3V. The regulator reduces 3.6V to 6V (e.g. 5V) to 3.3V. 8.4V is too much for the regulator and probably already destroyed it, which is why your HC-05 doesn't power up.

A single lipo cell might have worked.

Steve

If an LDO type regulator was used (likely) then these often have a max input voltage of 6.0V or 6.5V, so 8.4V would fry them.

I would assume a pin marked as 5V requires you to connect 5V, unless I had a data sheet (of board or regulator) which specified otherwise.

slipstick:
The chips on that board run at 3.3V. The regulator reduces 3.6V to 6V (e.g. 5V) to 3.3V. 8.4V is too much for the regulator and probably already destroyed it, which is why your HC-05 doesn't power up.

A single lipo cell might have worked.

Steve

First, I tried with a single lipo cell. But it didn't work.

hardik311095:
First, I tried with a single lipo cell. But it didn't work.

Useful info to have included in the first post perhaps.

[/quote]

srnet:
Useful info to have included in the first post perhaps.

Sorry, I forgot to mention it but single lipo cell wasn't enough either.

Does anyone know the smallest 5v battery that could power my module?

Just looking at that schematic again: the STATE pin of the HC-05 is connected to an Arduino pin marked DTR. I don't think that's going to work, either. DTR belongs to the USB interface. You probably need to use one of the Arduino's digital pins for that.