Controlling LED's using Pduino object in PD (Pure Data)

Hi , im relatively new at programming in general so this might be a stupid question and i apologise for that in advance. Im having pots and LED's hooked up to a Mux 2 shield ( i have 25 pots, 3 LED's, and 4 footswitches, hence the shield to expand inputs) which is then hooked up to an arduino mega. Iv set it up such that the arduino sends its serial data through usb to a raspberry pi ( where pd is running with a simple Tape delay patch) using the pduino object.

Question is I wanted to have the 3 Led's flash at the rate of the delay time set on each Head. which means Pd needs to alternate between high and low states of the particular digital output in question at the rate of the delay. How would be i able to achieve this?

Worth to note is that im currently using a version of firmata that has been modified by myself to make it more effecient.