Installation of HC-06 Bluetooth module in Megasquirt – Update


I noticed that the USB interface was not working after my original post regarding the BT mods. Long story short, was the BT serial interface was somehow interfering with the USB in the MS3 module. This post is how I fixed it (hopefully) and at the same time I wanted to have a BT light on the front panel as well as a ECU on light. My MS3 has the time and knock modules installed, and from memory the knock module uses the I/O ports driving the D14 – D16 LED’s, so their original functionality is lost, so I have used these for a switch to turn on/off the BT and have a nice blue light to show the status of the BT, and the last red LED I’m using just to show that the ECU has 5V power.


I purchased a miniature Double Pole Double Throw (DPDT) switch and a blue LED. This was used to individually switch both the +5V , as well as the TXD-1 (Pin 11 U6) which go to the HC-06 VCC and RX pins respectively. The GND and TX pins stay connected as per before.

You may notice compared to my previous posts, that the BT module is different, well it is because I accidentally blowed it up in my hast to find out why the USB was not working. Doh! Any ways, I had a spare, so there it is.

To power the blue BT status LED, I used the LED(24) pin to drive the top of R27-1 (warmup-1) 1k resistor. I lifted this end of the resistor from the PCB so it was no longer being driven from the MS3, I also changed the red LED D15 for the blue LED, and I had to change the R25 330R resistor to a 680R as the LED that I purchased at it’s rated current of 20MA could have been used for a laser at a rave, it was so bright.

The formula to calculate the resistor is (VCC – VF) / IF where VCC is the voltage applied, VF is the forward voltage of the LED and IF is the desired forward current. So in a normal blue LED, not my searchlight one, the resistor would be:

(5 – 3.2) / 0.02 = 90R so the nearest value would be 91R
In case your wondering, I had to lower the current to 2.6ma to get it to be visually acceptable.


It all seems to work now including USB connectivity (as long as you turn off the BT, hence switch). Let us know if I’ve left out any points. Please leave a comment if this has help you, it takes me a while to write these posts and it would be nice to get feedback good or bad.

HC-06 Module – Pins
Switch inserted into D14’s hole
Switch from front.
Pin 24 LED O/P on HC-06
My rat nest of wires!


MegaSquirt MS3 with HC-06 Bluetooth module
MegaSquirt MS3 with HC-06 Bluetooth module

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