SparkFun Forums

[BigC]

After 4 years of using the MP3 trigger V23 board built into my own circuit board, I have recently been shipped a batch of V24 boards which simply wouldn't trigger when connected to my circuit.
8 of the trigger inputs are driven via a ULN2803 driver (used as a simple inverter)
Studying the circuit diagrams of v23 against V24 I noticed an additional resistor R12, pulling up the common from the 4067 to 3.3V.
Removing this resistor allowed the triggers to work again correctly.
I'm guessing the fact that a LOW trigger from the 2803 is actually 0.6V and not 0V, and when combined with the 3.3V pullup, the trigger signal isn't seen.
My question is, why was the resistor added? Is its value of 1k too low?

Another slight nark with the new version is the missing connections underneath the output jack that I used to feed the audio back into my circuit board (I can live with that since AC coupling has been added!)

[robertsonics]

The pull-up resistor was added to address false triggering issues when people use long wires attached to contact closures. Specifically, when an input trigger was activated (shorted to ground) the next input on the analog switch which was not grounded occasionally did not rise fast enough and was detected as active low. Rather than slow the input scanning down, which would have increased latency, this was added to increase the weak internal pull-up provided by the PSoC input.

At least now it's a lot easier to remove it than it was to add it if you needed it.

Just out of curiosity, have you considered using the WAV Trigger instead? It does everything the MP3 Trigger does (except play MP3 files, which you can easily convert to wav format) and a lot more, it's the same price, and also doesn't have the input trigger restrictions that the MP3 Trigger's analog mux requires.

[BigC]

Thanks for the reply.
Make sense when I think about it! At least I know I shouldn't be causing issues by removing it, as there is very little chance of false triggers.

I keep thinking I should investigate the WAV board, but never seem to get time.
Is the board layout identical to the MP3 board, i.e. would I need to redesign my board for the positioning of the trigger pins, power pins, mounting holes? Does it have (or need) the AC coupling circuit?

Thanks,
Carl