MyoBridge - Direct Myo <-> Ardiuno Communication

by gilhrpenner

You guys are amazing!! Thank you very much!

I'll try it as soon as I get a logic level converter.

I'm too excited to wait till my logic level converter get's here, is there any other way I could do it without the logic converter? Maybe using resistors?

Other question, once I flashed the CC onto my bluetooth can I remove the wired it was soldered on reset, 2_1 and 2_2?

btw, good to know more people are bulding prosthetics with Myo and Arduino.
Here's one of the fingers I already have assembled http://s3.postimg.org/3pnyfjg37/20151128_094900.jpg

If you'd like to add me on skype to share ideas.. gilhrp@outlook.com

Thanks again

by eric_castro

I would suggest to leave the wires in P2_1, P2_2 and RSTB till you have succeeded to get a response from the Myo… since that's the only time you will know the bluetooth module is properly flashed. You may need to do this a few more times once you have all the elements. Also, valentinrol may release new firmware updates that you may want to get, so better keep them attached a bit longer

You can use resistors to build a voltage divider but none of us so far have been successful on that approach; better wait on that logic level converter!

But if you are very impatient, there's one more thing you can try if you have the tools, you can convert your current arduino from 5V to 3.3V by replacing the regulator as explained in this tutorial:
https://learn.adafruit.com/arduino-tips-tricks-and-techniques/3-3v-conversion

I look forward at seeing your prosthethic hand in action! I will be finishing my myo-controlled monocycle lights tomorrow, hopefully will have time to make a demo video too.

by gilhrpenner

Unfortunately I don't have all the tools to convert Arduino to 3.3v
I'll try to do something with resistors and if I successfully done that I'll post how I did.

by gilhrpenner

So I was able to convert 5v to 3.3v with resistors.
I used 4x 1m, 1x 680k, 1x 470k and according to my voltmeter it's exactly 3.3v.

BUT I read online that I shouldn't do it with resistors lol.
Any advice whether should I do it or not?

This is how I did it.

by wxirxn

by gilhrpenner
So I was able to convert 5v to 3.3v with resistors.I used 4x 1m, 1x 680k, 1x 470k and according to my voltmeter it's exactly 3.3v.BUT I read online that I shouldn't do it with resistors lol.Any advice whether should I do it or not?This is how I did it.

There's an easier way to drop the voltage down, and by that's using a voltage divider. Look at the first image on this page:
https://github.com/vroland/MyoBridge/wiki/Getting-Started-with-MyoBridge-Library

Digital pin 3 is connected to R1, which splits into 2 paths: one to the RX pin of the HM module and the other to R2 which connects to ground.

Basically, the output voltage from the voltage divider follows the following equation:
V(out) = (R2/(R1+R2)) * V(in)

In this case, V(out) = (3.3/(3.3+1.8)) * 5 = 3.235V

You don't have to stick with 1.8k and 3.3k resistors; most combinations in a R1:R2 ratio of 1:2 should work. (2/3 * 5 = 3.33V)

But as eric_castro has mentioned, I haven't been able to get it to work using a voltage divider. It should work for flashing the firmware (as it has for me), but I haven't had any luck getting the Arduino to communicate fully with the HM module using the MyoBridge library. A logic level converter would be more convenient and reliable.

Last edit: Nov. 28, 2015 03:41 PM

by gilhrpenner

@wxirxn Unfortunately I don't have a logic level converter and I really don't want to wait a few weeks to get one through ebay lol that's why I used resistors instead.
Now I'm having one issue trying to run CCLoader, if anyone can help me with that I appreciate

by wxirxn

by gilhrpenner
@wxirxn Unfortunately I don't have a logic level converter and I really don't want to wait a few weeks to get one through ebay lol that's why I used resistors instead. Now I'm having one issue trying to run CCLoader, if anyone can help me with that I appreciate

Is your Arduino connected to your HM-10? If you upload a photo of your set-up I can check it for you (:

by gilhrpenner

Yes, it's all connected.
3.3v to VCC
GND to GND
D4 to Reset
D5 to DD
D6 to DC

Don't laugh at my set-up

Doing everything with one hand sucks lol

by wxirxn

by gilhrpenner
Yes, it's all connected.
3.3v to VCC
GND to GND
D4 to Reset
D5 to DD
D6 to DC

Don't laugh at my set-up
Doing everything with one hand sucks lol

It seems that you have soldered the wires onto the wrong side of the HM-10 board. They should be on the left side, with the antenna facing the top. Also, D5 should be connected to DC and D6 to DD.

by wxirxn

by valentinrol
@wxirxn Thank you. Looks like it locks up when attempting to write to the Myo… Now it would be good to know what hardware you use (Arduino). You could also try to print out the firmware data before this point and see if this is corrent. Do do this, just write Serial.println(firmware_info.major), Serial.println(firmware_info.minor) and Serial.println(firmware_info.patch) before this point.

It prints:

0
0
0

So it's not able to read the firmware at all. I'll try again once I get a logic level converter. Thanks!

Last edit: Nov. 28, 2015 04:14 PM