Can I Drive a Logic Input from a RPi GPIO?

Look at page 10 of the 7330 schematics.

Each logic input has a pullup resistor to +5 V that can be defeated by removing a jumper. So, you will need to pull that jumper to prevent that source of +5 V from damaging your Pi's GPIO. (The pullup is provided in case the user wants to drive the logic input with a relay contact or an open-collector transistor.)

Next, you see 10k in series with the base of the NPN and 4.7k from the base to ground. That's a 3:1 voltage divider, meaning the voltage across the 4.7k will be 1/3 of the voltage you apply to the logic input.

A silicon NPN transistor requires about 0.7 V to turn on. Since it is preceded by a 3:1 divider, it takes about 2.1 volts at the logic input to turn on the NPN. For that reason, we refer to 2.1 V as the threshold voltage for all logic inputs (including the COR and CTCSS inputs). So, your 3.3 V logic should be enough to trigger any of those inputs as the load will be under 1 mA

[Tip from Bob, WA9FBO]

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