fuel gage




February 12th 2013




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Possi’s motorbike fuel gage

Electronic circuit diagram

I had transferred the circuit diagram onto a transparency foil and then developed based on the common printed circuit board production process with photo techniques the pcb. As replacement for the operation amplifier TL 081 CP (Conrad po-no. 175331), that does have only one amplifier installed, I used the TL 082 CP (Conrad po-no. 175340), which is fully compatible. Since the TL 081 CP is no longer available on the market, I continued the project using the TL 082 CP. To build the pcd module is relatively easy, but if you require more details, then look onto Possie’s website Possi.de.


circuit diagram


Assembly description

Both, the circuit board and the sensor should be installed into a metal housing. The sensor I’ve installed into an aluminum housing type (Conrad po-no. 520012) and the electronic circuit into an aluminum housing type (Conrad po-no. 541613). The cable connection from the sensor to the electronic circuit was done with a two wire shielded cable. This will avoid noise on the whole circuit generated by the generator or the electronic ignition box.

The sensor housing was connected to the shield of the sensor cable. The other side of the sensor cable was connected to the metal of the circuit board housing and to chassis ground. To avoid ground loops, we highly recommend to ensure that the shielded cable of the sensor line is only connected on one side to the chassis ground. Again thanks a lot to all the folks that have supplied so much feedback of their experience over the past years regarding that project.


Sensor installation

The sensor comes with two metal connection poles for electric crimp connectors. Solder the two wires from the sensor cable on that two poles. We do not recommend to use crimp connectors, since they oxidize over the time and produce then a high resistance making the unit to fail. During installation you need to ensure, that the flow direction marked on the sensor is connected in the correct way into the fuel pipe. Cut out an appropriate slice from the metal housing on both sides to fit the nozzles of the sensor. To fix the sensor inside the housing, we usually use hot-glue.

Since however the two nozzles have smaller diameters than most of the fuel tubes installed in motorbikes, you need to build an adapter to make it fit. You may purchase in a hardware store a copper pipe, that has an outer diameter that fits into the inside of your fuel tube, and an inner diameter that may approximately fit the outer diameter of the sensor nozzle. Cut an appropriate piece in length and solder a copper wire around one end. This will avoid that the tube may slip off afterwards.

The whole set is then built together by using a two component epoxy resin. To ensure that the epoxy flows perfect into that connection, you may heat it up by using a hair dryer. Before you start that job, you need to ensure that the sensor nozzle wholes are perfect covered and that no epoxy may drain in. I have used a piece of the shielded two wire cable, greased it a little bit that the epoxy wont stick and pressed it into the nozzles. After approximately ten minutes, the epoxy is hardened and the piece of cable can be removed from the nozzles.

sensor modifications
The drawing above shows the epoxy filling with blue color. The installation on the Honda Varadero is done in the fule line that goes from the two tank hoses to the fuel pump. (refer to photos below for more details)


Set calibration for a Honda Varadero

As initial value for the bicycle speedometer, you should start with 1960. Possi' s recommended value of 1400 results in a deviation of 35% on the Varadero. With 1960 the tolerance on my motorbike was less than 2% with a complete used gas tank content.

This however differs between motorbikes. So during refueling fill your gas tank fully up, compare the amount of fuel with the amount shown on the display, calculate the difference in percent, and then adjust your bicycle speedometer number by that percentage. At the latest after the third tank filling you will have the accuracy as described above.



sensor installation

cockipt view of Honda Varadero

The picture shows the sensor insztalled into a aluminum housing, Both tube ends are fatsened on the sensor nozzles with metal tube bands.

That’s the view to my Honda Varadero cockpit. On the right hand side of the Gramin GPS12 GPS receiver you see the bicycle speedometer that is used here as fuel meter. That BC700 speedometer does not show the speed, but the fuel used with an accuracy of 2%.

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