Senseo coffee automation (ATtiny 85, SG90)

Third go at automating my Senseo coffee maker: turn it on, wait for it to heat up, pour a cup of coffee and turn it off again.

First try was simple but hard to set up and not very reliable when pushing the buttons:

https://www.prusaprinters.org/prints/110353-universal-button-pusher-sg90-mg996r

Next iteration was robust and running for a couple of months; only drawback was slow speed for the steppers to turn the M5 pushing rods:

https://www.prusaprinters.org/prints/110331-linear-actuator-stepper-pusher-28byj-48-m5-rod

This version of much faster and still reliable ;-) :

https://youtube.com/shorts/s_PcQxmPolw

Main features:

• Simple electronics based on a attiny85 and SG90 servos
• Increasing force of servos with double threaded 8mm pitch about 20mm custom thread (pushing force >10N measured)
• Additional latching circuit court zero power consumption at idle
• Electric setup: old phone battery with Tp4056 for charging, latching circuit from electronoobs (see source link below, with IRF9540N and 2N2222 as transistor drop in replacement), small boost converter 3.7V → 5V, actual attiny85.
• Safety feature: program only starts if cup is in place (switch attached to machine)
• Code for flashing attiny85 is included, it is Arduino based. I'm not a programming hero; I've derived it on the “useless machine” code from bra lark over at thingiverse
• Small wiring writeup for attiny85: Pin 0: 1st servo, pin 1: 2nd servo, pin 2 safety switch (needs to be pulled low for “go”), pin 4: controlling latching circuit (needed to learn the hard way that pin 3 does not work for this… since it seems to be “high” on boot)

Source links:

https://electronoobs.com/eng_circuitos_tut61.php

https://www.thingiverse.com/thing:4561617