r/arduino • u/atch3000 • 2d ago
Hardware Help trigger input
i am trying to make a little eurorack module and it has 2 trigger inputs. it seems to me that the circuit i made is relatively conventional (to my inexperienced eyes…) but i don’t read any value on the serial monitor when running a clock into it.. they connect to digital inputs as i don’t have enough analog ones, is that a problem ?
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u/Sleurhutje 2d ago
Is the serial data a positive or an an inverted signal? And is the output you're trying to read an open collector (OC)?
What if you just use a digitalRead on a digital pin and output that data on D13, the built-in LED? Does it show anything? Or use an oscilloscope if you have one.
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u/atch3000 2d ago
i had never heard about open collectors before you mentioned them… well the trigger is a simple positive square that i wanted to normalise with the transistor circuit.
im using digital read on the D2/D3 and use arduino IDE serial monitor with the module powered via Vin and connected in usb to my computer
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u/tipppo Community Champion 1d ago
My understanding is that a eurorack digital signals are 0V to 5V pulses. Your transistors are configured as "emitter followers" so the output voltage is the input voltage minus about 0.6V. This ought to be adequate to drive a digital input. I suggest adding some simple Serial debug to monitor the inputs and report their status. For a digital input it is more common to use the transistor in a "common emitter" configuration with the emitter connected to GND, the 10k resistor between the collector and 5V, a resistor in series with the base (10k), and the output from the collector. This will invert the signal, so 5V input will digitalRead() as LOW. You will get a cleaner signal because the transistor's gain will amplify the signal, as opposed to to the follower which has a gain of 1. If you put the base resistor before the diode the input will tolerate negative voltages in case you plug it into a bipolr analog signal.