Micro Meastro lost his smoke

As we all know, electronics works on smoke.
I’ve got a Micro Meastro, which lost his…

After I connected a 2S (7.4V) lipo to my Micro Meastro (on the pins GND and Vin, next to the RX, TX, RST), it let out a puff of smoke.
I disconnected it, did a close inspection, but couldn’t find a fried component.
After this, I connected it to USB, a green led lights up, but thats it, no connection can be made.
Connected to a battery, nothing happens, no lights, no puffs, nothing.

According to the manual, the Vin is rated up to 16V, so 7,4 shouldn’t be a issue.
Where can I find the problem? I am fairly handy with a soldering iron.

I can make a zoomed-in photo of the circuit, but under a magnifying-glass I couldn’t find anything weird…

any idea’s on this one?


I am sorry to hear that you are having trouble with your Maestro! Did it work at all for you before this problem occurred? Also, does the green LED blink at all when connected to USB or just immediately light up?


Hi paul,
I tested the Micro with one servo, hooked up to my laptop, everything seemed to work ok at that moment.
I am also using 2 Meastro 18’s, they work perfectly, also hooked up to this 7.4V lipo.

The green light turns on the moment I connect the USB, no flashing though…


Are you also using the LiPo for servo power? How did you power it when you were testing with one servo? Have you made any modifications to the board to allow a single battery to go to servos and to Vin?


during testing servo power was provided by a 4cell nimh pack.

I was planning to use the micro as a programmable switch, to switch LED’s on and off.
Since these LED’s will be in a plane, weight is everything, thats why I was planning to use a 2cell lipo.
I didn’t made any modifications yet to power these LED’s
The micro is still stock, only with these pins soldered on, in a clean way.


I do not see any problem with what you are doing, and the Micro Maestro is very similar to the Mini Maestros, so the only thing I can think of is that you must have accidentally connected your battery power to the wrong pair of pins, like GND and +5V or VIN and RX, instantly destroying the Maestro’s microcontroller. Is that possible?

One thing you can check is the voltage on the +5V pin when plugged in to USB - if that is still at 5V but the board is not recognized by your computer, then unfortunately I do not think it is going to be fixable.


Hi Paul,
Connected to USB I do measure 5V on the 5V-out pins, nothing on the the 5Vin pins
Connected a battery to the 5Vin pins, I also find 5V on the 5V-out pins. No LED’s light up however…

I am sure I didnt connected the lipo to the +5Vout, as it is a different row of pins.
I am pretty sure I connected it correctly to the 5Vin, but as you can understand, I start to doubt that…

Thanks for the help so far :slight_smile:


Unfortunately, this just confirms that the microcontroller on the board is dead. I am sorry that there is nothing that I can do for you!

If it was because of an incorrect power connection, one thing that might help in the future is to get kit version of the Maestro and solder on a polarized power connector (like this one). That way, you only have to get it right once.


Hi Paul,
sorry to hear. Well, that’s life.

normally I get the polarity right, but its a good idea.

Thanks for the help


just an additional question.
Is the meastro range able to switch this 7.4V for LED’s?
As in, can I connect Vin to the + of the servo-rail, specified as outputs?
My LED’s can take up to 12V, so it saves me a relais…


Input pins on microcontrollers should never be connected to voltages higher than VCC, since there is an effective diode from each input pin to VCC. So I don’t recommend it unless you totally sure about what you are doing!

However, if the LED circuits you are talking about have at least a couple of LEDs in series so that they create a large enough voltage drop, your Maestro would never see more than 5V, so it could actually be okay. I would still recommend a MOSFET (instead of a relay?) so that you could be totally safe and potentially reach higher currents.


Hi Paul,
i will make some calculations for a resistor, so I dont exceed the 5V. If that doesnt give me enough light, i will go for the mosfet idea.


You are probably thinking about it the wrong way if you think the resistor matters. As a simple example, suppose your battery voltage is 8.5V when fully charged. When you are trying to turn the LED off, your circuit will be

5V “output” — LED — resistor — 8.5V

So if the LED voltage drop is 2V (one normal green LED), the resistor will have 1.5V across it, and the LED will be illuminated. You are going to see light unless you choose a ridiculously high resistor value. If the current is high enough (several mA?), the Maestro’s 5V line could rise, possibly as high as 7V, which could damage the Maestro. This will happen even if the line is an input or if the Maestro is in reset, because of the effective diode that I mentioned.

If the LED voltage drop is 6V (three normal green LEDs), there will be no current flowing and the LED will be off as desired. But watch out, because efficient LEDs might start conducting on at much lower voltages than you expect.