Maestro to sparkfun mp3

Continuing the discussion from Controlling MP3 Trigger with the Maestro:

Yes, thank you for your response. I noticed that I had swamped the channel, as I initially had the trigger on channel 1 and mistakenly swapped it when I took the pictures.

The tracks will play when I ground the pins.

Trigger 3 plays track 003.

If the slider is not working, should I try writing a script to bring the channel down? Would it be the same as a servo command?

I would not expect any differences between moving the slider and running a script to toggle the output.

Just to clarify, did you try doing the specific test I suggested (i.e. remove the red signal wire then use a jumper to connect the trigger pin on the MP3 Trigger to a ground pin on the Maestro)?

With the signal pin disconnected from the MP3 Trigger, could you try measuring the output from the Maestro (e.g. with a multimeter or scope) to see what it is doing when you move the slider around? If it appears to be going high and low as expected, could you try re-connecting it to the MP3 Trigger and repeat the test to see if it is any different?

Lastly, can you post updated pictures of your connections as well as a copy of your Maestro settings file? You can save a copy of your Maestro settings file form the “File” drop-down menu of the Maestro Control Center while the controller is connected.


I followed your suggestion and tested the trigger by swapping the ground pin and the trigger pin to the maestro. I was able to manipulate the triggers statue’s light using the Maestro sliders, but the MP3 trigger kept triggering under 1500µs, causing the statue’s light to blink rapidly and preventing the track from playing. Raising the slider turned off the trigger.

I’m wondering if I need to add a pull-down resistor to the circuit or a relay to each trigger to fix this problem. At this point, it may be easier to just use my Mini Maestro with the serial interface but would be disappointing as I rather use the trigger pins

It sounds like you might have misunderstood what I was suggesting; if you swapped the signal and ground wires, you are shorting out the Maestro’s signal pin to ground, which could damage it. Since you’re still having trouble getting it to work properly, I recommend removing all of your connections (including the ones for the button) and then only making the two following connections:

Where the blue wire is the ground connection and the orange wire is the signal.

With those connections, the track should start playing as soon as you drag the channel 0 slider below 1500μs.

Please note that the trigger pins on the MP3 Trigger already have an internal pull-up resistor, and the Maestro should be driving them low to trigger the audio track, so you should not need to add any pull-down resistors.

If that does not work, then I suggest manually grounding the trigger pin to a ground on the Maestro, which you can do by leaving the (blue) ground wire and connecting the signal wire to a ground pin on the Maestro instead, like this:


Thank you for your reply. I tried both of your suggestions, but neither worked. So, I went ahead and did some testing. I put a 100 ohm resistor in the circuit, and it worked. With a little more testing, I found that I could go up to 820 ohms, as it was the highest value resistor I had before 1k ohm. Anything above 1k ohm did not work

I am glad you were able to get it to work; thank you for sharing your solution!

With that information, I went back and looked at the MP3 Trigger schematic more closely and noticed that SparkFun uses a stronger pull-up resistor than I was expecting (1kΩ). The Maestro and MP3 Trigger signal lines also have in-line protection resistors (220Ω and 100Ω respectively) built in. So, when the Maestro channel is driven low, it creates a voltage divider, and it doesn’t quite overcome the 1kΩ pull-up.