So this Lazy Old Geek (L.O.G.) got another Bluetooth HC05. I have written up some of my Bluetooth experiences in the following:

https://www.instructables.com/id/OldMan-and-Blueto...

This HC05 is different from the first ones I bought. Since I get easily confused, I wanted to make this one electrically compatible with the HC05s I modified in Bluetooth2.

My HC05s are modified to work with 3.3Vdc and will go into Command mode if the EN pin is pulled up to 3.3V. The first schematic is pretty much what I have (I noticed that some of the resistor values are different).

To make it 3.3V I needed to jumper around D1 and IC1(voltage regulator), I also removed the voltage regulator.

To make EN work, I needed to remove R2 and add a jumper from the EN pin to PIO11 (one side of button, S1).

See schematics and pictures.

WARNING: This is very a delicate procedure to remove the two components. I used a very small soldering iron tip and some magnifying glasses.

When I modify parts for 3.3V operation, I like to add a yellow dot (nail polish) to indicate 3.3V.

This HC05 now works the same as my other HC05.

Step 1: PCB for HC05/HC06 to CP2102

So instead of using a Breadboard for these modules, I made a PCB for my 3.3V CP2102 to 3.3V HC05 module. It also works for the HC06.

I used this Instructable to make this PCB:

https://www.instructables.com/id/Vinyl-Sticker-PCB...

The Eagle Cadsoft schematic and board files are attached.

NOTE: My 3.3V CP2102 modules do not have polarized connectors so they can be easily reversed. I use red nail polish on both the CP2102 and the Adapter PCB to indicate the non-ground side of the connector.

NOTE: The HC05/HC06s do not have polarized connectors so they can be easily reversed. I labeled the connector for correct orientation. Some HC06 are four pin and use the middle 4 pins.

The two pin connector is used to put the HC05 into command mode. In run mode, it is un-jumpered.

I use these adapters for testing new HC05/HC06 modules and for connecting a HC06 to a PC when it’s receiving data from an Arduino/HC05.

Using these adapters, frees up a Breadboard and some jumpers.