quad-386 coffee heater

Who says CPUs waste energy by producing heat? - It can be used to warm coffee!
A USB-driven, temperature-monitored quad-386 coffee heater.

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The goal of this project is to build a coffee (tea perhaps in V2) cup warmer ("coffee heater") using four CPUs for producing the heat. In the pictured prototype the used CPUs are variations of the good old 386. The heat production is controlled by changing the duty cycle of reset assertion. In addition the built-in self test is used to make the CPU being active. The temperature is monitored via four DS18B20 sensors and sent via an AVR using V-USB to the PC, where a python-ncurses tool is used to display it (see screenshot using "Cathode" on OS X).

Project status

  • Prototype PCB assembled
  • V-USB communication working
  • one-wire temperature sensors working
  • LEDs working
  • User interface ready
  • Case machined
  • Heating to be debugged (seems to be some power-up latchup problem and/or partly broken CPUs)
  • Twitter account!?!

Openess and Connectivity

Schematics and PCB are done using EAGLE. Apart that only open source tools where used. Special emphasis being on the ruby-script generated gcode (that was fun!). Some cross-checks on the licenses of the used libraries needs to be done and I am looking forward to publishing sources.

Connectivity? Yes!

  • Monitor and log the temperature at 4 places!
  • Show status on 4 LEDs!

How would you do without?!?

  • 4 × 386 Microprocessor, some different variants, PGA132
  • 1 × ATtiny461 Microcontroller, SMD SO20
  • 4 × DS18B20 One-wire temperature sensor, SMD SO08
  • 4 × LED, red SMD, 0805
  • 18 × capacitor, 100nF SMD, 0603

View all 13 components

  • Project status...

    magnustron12/01/2015 at 19:18 0 comments

    Dear followers,

    thanks for being interested in this project! Unfortunately, I do not have not had much time to work on it. As mentioned in the status, the heating is causing some headache. These are some observations:

    • It seems one needs to be very careful switching the CPUs on. Initially, I had foreseen a reed-relay for this. Too crude, I fear. When turning on, some CPU starts to heat up quickly, while others do not. The one getting hot changes with power cycle.
    • Switching on the CPUs too sudden also caused a break down of board voltage, which caused the USB connection to become unstable.
    • I could not find sockets for the CPUs and soldered them directly on the PCB, which makes troubleshooting now quite difficult. Moreover they are powered in parallel. I have the suspicion that some CPU is broken.
    • Software USB and one-wire does not go well together. I have not figured out a solid way to make this stable. Either USB interrupts the one wire timing, or - with USB interrupts disabled during one wire transactions - USB becomes unstable.

    Summary: while temperature monitoring and LED blinking works like a charm, powering the CPUs was so far not successful in a reproducible manner and I could not verify that the idea of periodically triggering the self-test would really work.

  • Updated project page

    magnustron08/20/2014 at 23:18 0 comments

    Well, finally, I've found the time to update the page with more details on the project! Enjoy!

View all 2 project logs

  • 1
    Step 1

    Produce PCB

    This is an ordinary 8x8 cm^2 double-sided PCB. Got mine done at WE direkt.

  • 2
    Step 2

    Populate PCB

    This is best done step by step. For the processors, I'd loved to had sockets...

  • 3
    Step 3

    Produce case

    Get a pice of wood and a CNC machine - my great thanks to Paul for installing the Badog X2 @ PTL. You can use the provided ruby script to directly generate gcodes.

    Here are a pic from one of the first trials. Its scaled down to one CPU (perhaps the "Espresso"-version)

    Here actually a nice and - very helpful - simulation with OpenSCAM:

View all 6 instructions

Enjoy this project?



Edgar Kogler wrote 02/23/2024 at 14:40 point

great ! This surpasses even the Commodore-64-PowerSupply Coffee-Heater !

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mohsinirshad494 wrote 05/11/2022 at 16:20 point

that is great project and I am really impressed. Kindly visit my webpage to check my projects here

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veerun zek wrote 02/04/2021 at 11:45 point

yes i now these types of coffee heaters are very useful in these days they have so many advantages and so much facilities they provide i am also working on the same project you can see here

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martingallispe wrote 12/19/2020 at 03:12 point

I like this project. Can we use it for different brands of coffee, you can see here detail

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zivimo wrote 11/26/2016 at 14:21 point

Hey Magnus,

could you make the Eagle and source files available? I really would like to build my own coffee warmer!


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Witek wrote 10/21/2016 at 23:10 point

I think you could actually consider clocking the cores and switching the clock frequency depending on core temperature. Also it would be *like super cool* to measure the temperature using PN-junction characteristics of the silicon inside (e.g. clipping diodes).

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Kn/vD wrote 08/18/2016 at 06:03 point

I like the project, but it makes me little sad at the same time seeing the great 386 processor being reduced to a dumb heater

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Yann Guidon / YGDES wrote 08/18/2016 at 15:50 point

It's not a dumb heater. It's a heater but it's far from dumb :-D

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Arduino Enigma wrote 08/30/2018 at 01:33 point

I was not aware the mighty 386 got warm during normal use. Something might be wrong with the one that gets warm.

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Arduino Enigma wrote 08/30/2018 at 01:33 point

Sad indeed...

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Joakim L. Christiansen wrote 08/13/2016 at 18:45 point

Can you have it mine Bitcoins?

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Psy Chip wrote 08/13/2016 at 17:15 point

haha! laugh at loud :D also i got two pairs of 486 cpu's which laying around since 10 years. i can send them to you if you wish.

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Arduino Enigma wrote 08/30/2018 at 01:39 point

CPUs did not start requiring active cooling until the Pentium was introduced. I don't think even the DX4 100 needed cooling. Cyrix 686 on the other hand....

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magnustron wrote 08/30/2018 at 07:13 point

Well, at least I remember having nearly burnt my finger on a working 40MHz 386 compatible (AMD?). 386s do comsume a few watts -- typically enough to get decently warm/hot. Anyhow, sad, yes! But, also makes me remeber the good times whenever looking at it! Would really like to find the time to do this again with Pentium 60/66/90s, this time adding a bit of memory + I/O.

Now, you made me think of the (evaporative) cooling power of a cup of coffee!

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Tillo wrote 12/05/2015 at 21:56 point

That project is so great. 

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Eric Hertz wrote 11/07/2015 at 03:39 point

I dig it, and clever to use the self-test mode to get 'em chugging!

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Roobotics wrote 10/24/2015 at 09:15 point

Hah, this is hilarious and amazing at the same time, a very clever little conversation starter as well. Also for availability's sake you might want to switch to 486 processors, those are still easy to find, 286/386 are much more rare these days.

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Crypto [Neo] wrote 04/17/2015 at 06:13 point

Haha, omg this is great! I remember having 3-4 386 and 486 computers at one point :) it's funny what we're using the hardware for now.

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Dylan Bleier wrote 04/15/2015 at 03:34 point

in 15 years will we be doing this with 64 bit processors?

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Christoph wrote 08/20/2014 at 07:12 point
Aaahahaha this is great!

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OneShot Willie wrote 08/20/2014 at 02:46 point
I think you have to use 286s for tea...

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magnustron wrote 08/20/2014 at 05:42 point
Do you have a good source? These four 386 were already quite hard to get (and I am not yet sure they work) - and came without sockets (if you look closely, they are soldered by directly to the PCB).

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zuul wrote 08/20/2014 at 00:54 point

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Mic wrote 08/19/2014 at 21:41 point
Really nice project, can't wait for the tea-compatible version!

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