show the Oil temperature directly after start in your VW Golf 3:

Golf 3 Tacho MFA

The VR6 Engine is very picky with its oil temps, so every drivers first steps after starting the engine is hittin the MFA switch 5 times to see the oil temp in the so called "MFA-Display".

Why not make this automaticaly?


A ATtiny12 or ATtiny13 with a Transistor is all it takes to make this task for you 😇




it is small enough to go right into the gauge cluster of the Golf! See the Breadboard version on top of my "Debug" Unit:


MFA Umschalter Debug

The code is also simple! It waits 1sec after ignition is on, then switches the transitor 5 times and then goes to sleep.

Its written in Assembler as the AVRStudio cannot compile with the AVR-GCC for the ATtiny12...

ATtiny12 programmer with AVRMK2

Projekt: MFA Umschalter

Automatisches Anwählen der Öltemperatur
im Golf 3 VR6 Tacho

Date: 21.09.2011
Autor: Stephan Martin

.include ""        //ATtiny12, Adjust to if ATtiny13

sbi    DDRB, 4    ; output on Pin 5

ldi  R17, $0A
WGLOOP2:  ldi  R18, $C6
WGLOOP3:  ldi  R19, $C9
WGLOOP4:  dec  R19
brne WGLOOP4
dec  R18
brne WGLOOP3
dec  R17
brne WGLOOP2

//Pin 5x Toggeln

rcall toggle
rcall toggle
rcall toggle
rcall toggle
rcall toggle

//And Sleep!

ldi r16, 0b00110001        //Power Down and Sleep Enabled
out MCUCR, r16

//in case of broken sleep:

loop:    rjmp loop


//Toggle Subroutine

sbi PORTB, 4
rcall delay
cbi PORTB, 4
rcall delay

//delaying 0,1sec (at 1,2MHZ internal):
ldi  R17, $C7
WGLOOP0:  ldi  R18, $C8
WGLOOP1:  dec  R18
brne WGLOOP1
dec  R17
brne WGLOOP0


This should work on a ATtiny12 or ATtiny13! A great tool for getting the timing right is here:

I did not even made a circuit board for it, just take a piece of breadboard and make it 😃


DL1DOW got me on the Idea for this, his project had the same idea, but i thought i can make it smaller 😉

Hackaday got it postet:

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