This is my solution to fix the display on a combined VDO tachometer/hourmeter, which is used in many OEM installations, including Isuzu, Volvo Penta, Yanmar, and many others.

Software (complete, with source code), and mounting instructions can be found below.

My solution is based on an idea from a member (Stuart) on the Canal World Forums. You can find additional background information including some details of how to fit everything in the VDO enclosure there.

Update April 2022

This repair has now been running for seven years on my boat without any issues.

Update February 2020

It seems that www.boatstuff.se has stopped selling the replacement displays, but you can find some Chineese version on ebay for about 20 USD.

Meanwhile I've got some requests for supporting a 128x32 Arduino OLED display and moving the text to a different position on the display, so I've made a new release 3 you can find below.

Conor McLoughlin has written an excellent document showing how he has installed the 128x32 OLED display in a Yanmar VDO hour meter. It seems to be a smaller unit than mine, hence the smaller display is required. His writeup can be found here.

Update December 2016

This repair has now been running for two years on my boat without any issues. Initially I was a bit worried about the OLED and humidity combination, but it does not seem to be a problem. Also the hour meter is very easy to read at night, and a bit difficult to read during daylight. However I have a hunch that the original display would be no better during daylight, and certainly much worse during night.

Also note that boatstuff.se started selling replacements of the original display in the spring of 2016 (they have since stopped selling them). They're quite pricy, though at ~65 EUR, and they'll likely also have a limited lifespan. The proposed OLED solution shown here should be well below 10 EUR.

Arduino code for VDO repair

Use this code to have the Arduino Nano convert the 7-segment LCD memory map to OLED memory map.

If you find this useful, a small donation would be greatly appreciated :-) Use the contact form to request my paypal account. Of course you can also use the contact form if you have any questions!

Release 3 (February 2020) To use:   1. Install the Arduino IDE. I used version 1.8.11, but newer versions probably works too.   2. Import the OLED directory as an Arduino library   3. Compile and download this sketch   4. Enjoy Release 3 has now been uploaded, it has the following improvements: - Works with current Arduino IDE (1.8.11) - Supports 128x32 OLED display (along with 128x64 OLED display, as before) - Supports vertical adjustment of the image on the display - Option to flip display 180 degrees - Fixed a bug where 7 was shown incorrectly on some VDO displays when using Arial style font Note that the OLED library has changed from the previous releases, so if you already installed the release 1 or release 2 version you have to manually overwrite the files in your "My Documents/Arduino" folder. Also note that the splash screen tool has changed from the previous release, so make sure you use the one provided with this release. It is also called "Release 3" in an attempt to cause less confusion. Download the "release 3" Arduino code Unless I get feedback about problems or feature requests I consider this the final version.

Release 2 (January 2015) To use:   1. Install the Arduino IDE version 1.0.6     Note: It has to be version 1.0.6 as the newer 1.6 series uses an new GNU compiler, which seems to be incompatible with older code, including this.   2. Import the OLED directory as an Arduino library   3. Compile and download this sketch   4. Enjoy Release 2 has now been uploaded, it has the following improvements: - Nicer Arial style font - 7-segment font - A tool to convert a picture into a startup splashscreen, so you can have the name of your boat shown on startup Note that the OLED library has changed, so if you already installed the release 1 version you have to manually overwrite the files in your "My Documents/Arduino" folder. Download the "release 2" Arduino code

Possible Improvements

- Put Arduino to sleep mode.
- Power consumption has been increased quite a bit with the LED and Arduino. Hopefully not too much!

Connections

First connect the Arduino to the OLED display, as shown in the diagram below. Then download the code. When everything is good to go, connect the VDO unit to the Arduino. Note that the Vin pin should not be used as it is connected to a power regulator. Instead you can use the Vcc pin and there is a second Vcc pin in the 6-pin ISP programming header, if you don't want to connect two wires to the same hole (it's not really meant for two wires, so it's not super-easy to fit).

When the Arduino Vcc is connected to the VDO display you need to have 12V power on the VDO unit while the USB cable is connected to the Arduino. Otherwise the VDO unit is drawing too much current from the USB connection so the Arduino will not function. Your Arduino Nano should have a diode between the USB power and Vcc, which means that it is safe to connect USB power while the VDO powers Vcc on the Arduino. However it is possible that certain cheap knock-offs are not fitted with this in order to save two cents, so be careful!

Btw: I used an Arduino Nano without pin headers mounted. There was not enough room in my VDO case for the pins to fit.

Diagram

Pictures

The transparent plastic milled to fit the OLED display. I deliberately tried to avoid cutting the outer circular part. It is used to reflect the red light onto the unit. The hole is for the wires and the deepeed areas are because some of the capacitors are a little raised. I used a Proxxon tool with a suitable milling bit.	OLED display fits perfectly!
Cover added. The protective film on the OLED display is still fitted.
The PCB with wires and LED mounted.	The PCB with the high bright red LED mounted.
I had to mill the rear cover a little in order for the LED connections to fit.	Mounted and glued. I used silicon coating, but you can use any glue.
It just barely fits with the Arduino!	From the other side.
Powered up with the custom logo. You can easily create your own using Paint and the tool I created.	Hour counter now working.
The VDO programming modes also work.	The VDO programming modes also work.
One picture of the arial style font. I forgot to take it after putting the instrument together..