Add rapid fire to Daemonbite pro micro

[msknight]

I'm going to show my complete noviceness here.

I have a joystick I built using a pro micro and Daemonbite's free software. Here's the overview -
https://github.com/MickGyver/DaemonBite-Arcade-Encoder

To "fire" a button, I'm connecting the pin to the ground. So far so good.

Now I want to convert it to quick fire using a 555 as per this...
https://www.instructables.com/Add-a-rap ... ng-a-555-/

Initially, I thought, "Ok, I simply wire the "To Mouse" to the pin I want to fire on.

Then I thought... hang on... if I fire a button by connecting the pin to ground, then it surely can't be that the promicro is detecting by receiving a voltage on that pin... because I'm connecting it to ground... so that must mean that the pin is generating the 5v... and if so, then how is it detecting that I've, "fired," it... and what does that mean for me wiring in the autofire 555 circuit?

I'd be grateful for insight into how this is working please, as I clearly need to learn about this.

[julie_m]

The "fire" input is ordinarily connected to +5V via a "pull-up" resistor (which probably is inside the microcontroller), so it reads logic high (1).

When the input is connected to 0V, either by the "fire" switch or the output switching transistor in the 555 timer, it will read logic low (0).

The pull-up resistor limits the amount of current flowing to ground.

[msknight]

So if I read that correctly, what I need to do is use the pulse output of the 555 timer, to operate an electronic switch which will connect the Pro Micro pin to ground when there is current coming out of the 555 ?

[msknight]

Or should I be looking at doing this some other way than trying to adapt that 555 circuit?

[julie_m]

Pin 7 of the 555 is an open collector NPN transistor (or an open-drain N-channel MOSFET, in the low-power 7555 version) which is used to discharge the timing capacitor. So you could try connecting a diode with the cathode (business end) to pin 7 of the 555, and the anode to the side of the fire button that would originally have gone to ground. This ought to pull it low enough to read as a logic 0 when the button is pressed.

Alternatively, if there is room in the Pro Micro and you are comfortable with writing Arduino code, you could use a software timing loop to pulse the "fire" input.

[msknight]

Many thanks. I'll give that a try.