WARNING!

This PCB is powered from 5V that comes from the power management board inside the ultrasonic cleaner. To access this timer board, cleaner has to be opened AND MAINS CONNECTED CIRCUIT IS EXPOSED! The power board has capacitors and other parts of the circuit that can be dangerous! If you open your ultrasonic cleaner and do any modifications to it, you are doing it at your risk.

Simple project to fix significant problem

It's time to finally fix the main issue I've had with household ultrasonic cleaners: Too short maximum timer duration.

Luckily microcontroller that handles the timer is in a separate PCB with the buttons and display and all the power handling and transducer driving stuff is in a separate PCB. These boards are connected with four wires: 5V, GND and two IO pins. One IO controls heater element (not powerful enough, I decided not to use it) and another controls the main ultrasonic transducer driver.

What's not working/implemented

Heating element and temperature reading haven't been tested. The heating element is in my opinion too small to be useful, so I didn't bother using it. Circuit is there, if someone wants to go and tinker with it.

SOFTWARE/Sketch

I can't find the sketch for this. But it's countdown clock with I2C oled as a display, few switches and two regular outputs for the cleaner/heater. Should be pretty trivial to write your own implementation.

Modifications since video?

You can see this project in a video embedded below. I did update the layout to use 0603 resistors and capacitors, instead of 0402. I use 0603 components if there isn't real reason to go smaller or larger. THIS VERSION HASN'T BEEN TESTED! Try at your own risk. But KiCad's DRC (Design Rules Check) didn't find any errors, apart from some silkscreen areas overlapping or being clipped by board outline... Nothing that affects functionality.

Component sizes

Resistors and capacitors are 0603, like mentioned above. In the demo video, they were 0402.

Connectors and 3mm LEDs are reused from the original PCB.

The 16MHz resonator is 3.0mmx1.1mm smd version.

Buttons are the usual 6mm tactile switches, see the original board to see the dimensions. Switches from the original PCB can be reused.

Pin functions

Switces from left to right are connected to PD4-PD2, internal pull-ups should be used.

PD0 controls ultrasonic cleaner element (Active high)

PD1 controls heating element (Active high), NOT TESTED

PC0 (A0) is temperature sensor's output, NOT TESTED

PC1 Controls the status LED

Video