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Topic: Power HC-05 via digital Pin? (Read 424 times) previous topic - next topic

couka

May 18, 2016, 11:54 am Last Edit: May 18, 2016, 12:01 pm by couka
Hello everyone :)

For a remote control application I'm using an HC-05 Bluetooth module.
Since the remote has no on/off switch I want to be able to cut power from the module before setting the arduino to sleep.

I thought it should be no problem to power the module by digitalPin 11, but when I do so, the voltage reaches only about 2,2V.

I'm using an arduino Pro Mini which should be able to deliver 40mA per Pin. I was told the HC-05 takes 35mA max.

Unfortunately I cannot measure the current, because the case of the remote sits a LITTLE bit tighter than planned :D

I hope to find a solution without another extra transistor, since another piece of wire and TO92 would hardly find any place :P

lg, couka
youtube.com/DieBastler1234
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PaulS

Quote
I was told the HC-05 takes 35mA max.
I think you were lied to. The thing is, first and foremost, a radio. Radios take more current than that.

You could use a digital pin to turn on, or off, a transistor that controls the higher amperage connection.
The art of getting good answers lies in asking good questions.

couka

#2
May 18, 2016, 12:07 pm Last Edit: May 18, 2016, 01:04 pm by couka
Radios take more current than that..
Ok... I found 35mA plausible, because the nRF24L01+ I intended to use before only took 15mA...

I'll try using a transistor then :/

Thank you,

lg, couka

edit: Transistor (NPN BC337)solved the problem. The HC-05 module actually draws ~70mA without connection and 56mA while sending. I guess the reason why it draws more in Idle than while sending is that the status-LED is on more often.
youtube.com/DieBastler1234
Don't send me technical questions via PM. They will be deleted unanswered.

PaulS

Quote
I guess the reason why it draws more in Idle than while sending is that the status-LED is on more often.
Listening requires more effort than talking.
The art of getting good answers lies in asking good questions.

couka

Listening requires more effort than talking.
Hehe :D

I did some additional tests and found, that the transistor solution works, but the HC-05 still draws ~0.9mA. I don't know exactly what the current path looks like, because I only measured the battery current with and without the Vcc-pin of the HC-05 connected.

My (dirty) solution now is combining 2 arduino digitalPins (11 and A4) to power the HC-05, which seems to work fine.
Using the Narcoleptic library, the arduino takes 150µA (depends on battery voltage) while sleeping now. Still a bit more than expected, but acceptable.

lg, couka
youtube.com/DieBastler1234
Don't send me technical questions via PM. They will be deleted unanswered.

couka

News!

The solution to my problem is so obvious, that I had no chance to find it :D
The breakout module that the HC-05 sits on has an onboard voltage regulator, which can be switched off by pulling the EN-PIN of the module to GND.

Many tutorials about these modules assume that there is a KEY-Pin instead of the EN-Pin, which at least for my modules is not the case.

Unfortunately my DMM has such an high internal resistance on the mA and µA-range, that there is a significant voltage drop at >10mA. I guess that caused some of the power problems I had before...

lg, couka
youtube.com/DieBastler1234
Don't send me technical questions via PM. They will be deleted unanswered.

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