ATtiny85 Kettle Thermostat

Description

In progress... building a thermostat that can be used to control any kettle for lower-than-boiling temperature water. Could also be used with a slow cooker or rice cooker or something as a sous-vide I guess.

This is version 0.3 I guess? I just keep trying new stuff a little bit at a time.

I'll upload code to github soon.

Details

Originally started with a digispark, right now using a bare ATtiny85 - MIGHT need to switch to ATtiny84 for more pins... I just have to go get one!

Currently using an I2C 16x2 display which is overkill and too big, going to switch to 7 segment LED x 2 I think plus shift register(s).

Currently using a mini pot for temperature set, may switch to +/- buttons.

Currently have no relay connected, just a piezo beeper when water reaches correct temp.

First used High-low tech method for programming ATtiny, but switched to arduino-tiny cores in order to gain tone() support for my piezo. I think the arduino-tiny cores seem to work a little better anyway, although it's SLIGHTLY more work to install them.

I'm using an Arduino UNO to program ATtinys right now using a custom "shield" (some pins and wires soldered to a socket and a glob of hot glue) according to the diagrams at high-low tech.

Currently powered by rechargeable USB li-po battery/power supply... going to include a 5v switching power supply from a half-broken phone charger hidden in the case.

Ideally, in the end, I will plug this unit into the wall, plug the kettle into this, and dip the thermometer into the water. Everything will be contained in as small a package as possible. Probably will cost more than a proper temp-controlled kettle but I travel a bunch and drink tea that needs the water to be ~75*C. Plus this is a fun way to learn to push the ATtiny for small embedded projects.

Components

1 × ATtiny85 OR ATtiny84

1 × 16x2 LCD display (I2C)

1 × 5v battery power supply (or whatever) I'm using a powerstick power shot that I got for free at SXSW

1 × Arduino Uno plus a breadboard, jumper cables, and a 10uf cap for programming ATtiny

1 × DS18B20 waterproof digital thermometer the one epoxied in a steel case WITH FOOD SAFE shrink wrap

Discussions

BrendanMatkin wrote 04/10/2014 at 18:12

My relay was actually 12v and not working properly (oops). So I haven't made much progress... the tone library not working properly with arduino-tiny on attiny84 is a known issue, not sure if there is a real solution other than shifting the frequency like I did.

I'll post updated code and pictures evenetually, or sooner if someone requests it!

At this stage the whole unit is a backpack on the relay with leads out to the tiny 2-digit display. Nice and super tiny, it's very satisfying.

Are you sure? yes | no

Momcilo wrote 07/10/2018 at 22:37

Hi Brendan,

I would appreciate if you could post a code for tone for Attiny84.

Regards.

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Eric Evenchick wrote 04/09/2014 at 19:18

Any advice on where to get a food-grade DS18B20? I'd be a little bit worried about boiling a sketchy one from China in my food...

Are you sure? yes | no

BrendanMatkin wrote 04/10/2014 at 18:08

I got a cheezy stainless one from ebay then bought my own food-grade heat shrink locally (I think it was an adafruit product: http://www.adafruit.com/products/1020)

Are you sure? yes | no

Eric Evenchick wrote 04/10/2014 at 20:40

I did not know food-grade heat shrink was a thing. Thanks!

Are you sure? yes | no

BrendanMatkin wrote 02/27/2014 at 06:26

Status update! I've bread-boarded v0.4:
** working on the ATtiny84
** relay is working (not hooked up to 120v)
** 2-digit 7 seg LED is working through non-latched shift register making it as small as possible)
** thermometer is reading asynchronously (as not to interrupt LED display). I might shift to a latched shift register in order to just avoid this, I have a spare pin and an extra $0.20.
** Buzzer now plays two-tone mario-style sound just for fun (actually tricky at 8 MHz without delay for some reason).

Are you sure? yes | no

Marko Dragoslavic wrote 02/20/2014 at 07:25

Interesting project. Put piezo beeper on PWM pin and control duty cycle according to temperature.

Are you sure? yes | no

BrendanMatkin wrote 02/27/2014 at 05:53

Hey that's a cool idea that I never thought of! Right now it just makes a two-tone alarm that sounds like it came from super mario brothers when it reaches the pre-set temp. Since I don't have a relay hooked up, this is currently how I know to turn off the kettle..

If you try something like this, let me know how well it works (I'll do the same if I beat you to it)!

Are you sure? yes | no

ATtiny85 Kettle Thermostat

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