Triggering toy from modular synth.

CrowleyE · Joined: Aug 16, 2019 Posts: 2 Location: London

Hi All.

I am trying to trigger a circuit bent toy with a gate or trigger from Mutable instruments Grids on my modular synth.

I am using a 2N3904 transistor as a spdt switch with no success.

Is one of this toys, and i am connecting them like this.

Base connected to the tip of the jack, and Emitter and collector to both sides of the toy to close the connection.

Also tried wiring the ground of the jack to the ground of the toy.

Sorry if all this sounds stupid.
Thanks so much

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blue hell · Posted: Fri Aug 16, 2019 3:54 am Post subject:

No base current limiting resistor used? that might have fried the transistor Confused

Also C and E should be connected to the right polarities ... also the transistor must be the correct type .. prolly NPN.

oh, and welcome

of course

CrowleyE · Joined: Aug 16, 2019 Posts: 2 Location: London

Thanks Bluepill for the welcome and answer.

Yes, the 2N3904 is a NPN transistor.
I might fried every single transistor that i tried without the limiting resistor, true.

but I think the buttons of the toy is a matrix button, so there is no polarity there.
Maybe i should use something else instead of the transistor.

Thanks again.

PHOBoS · Posted: Fri Aug 16, 2019 7:36 am Post subject:

For interfacing with toys I recommend using an optocoupler, especially since toys often work on a low voltage
so this will prevent any damage if you use a higher voltage to control it. It can also keep some noise out since
there is no electrical connection. I've used the CNY17 myself but there are other optocouplers that will work.
note: an optocoupler is not the same as a vactrol

You could add a driver for the input side of the optocoupler but in my experience that's usually not necessary and
a resistor to limit the current is all that's needed. You can experiment with how you connect the collector/emitter,
sometimes it works in both directions. If you are connecting it to a modular synth it might also be a good idea to
add a diode (something like 1N4148) antiparallel (opposite direction) with the LED in the optocoupler. This will
prevent possible damage to that LED from a negative voltage.

btw did you also connect the GND (sleeve) ?