Problems with PIC16F876A

[Plateau]

Hello folks, are you fine?

I am developing a solution to convert the range of the resistence meter of my car's fuel tank to another range because the new dashboard does not work correctly. The original meter works with a range between 0 (empty) and 90(full) Ohms
and the new meter works with a range between 44(full) and 290(empty) Ohms.

The configuration of 16F876A is:



Using CCs as the compiler, I have created a logic in wich according to the voltage value that was read I set one of the output pins as LOW (output_low) and all of others as FLOAT(output_float) and that's why the PAINEL resistence value (an output in the image above) related to VSS (GND) is 20 Ohms (from PIC) + resistor associated on the pin (example: PIN_A1 -> 20 + 22 Ohms). When I measure the ohm value with a multimeter the value is OK but when I make a voltage divider using a 50 Ohm permanent resistor the voltage value is too wrong, i.e when PAINEL has 263 Ohm in the output and the input voltage of the voltage divider is 10v the resulting voltage is wrong (the correct should be 8.4v but the measured is 6v).

When I simulate in ISIS Proteus this problem does not occur.

Can anybody help me?

Regards,

Pedro Rosa!

 

[bigdogguru]

The description of the problem provided in your initial post is rather unclear.

Perhaps, there is a simpler solution than the rather complex solution presented. Or perhaps not.

To better understand the issue at hand, please clarify the scenario.

You have replaced the fuel gauge in your vehicle and the new fuel gauges specs significantly differ for the original. Correct?

Is the current fuel tank level sensor simply a variable resistor actuated by a float with 0 Ohms representing Empty and 90 Ohms representing Full?

Do these fuel gauges display the fuel level based on an inputted voltage level derived from a resistive voltage divider which includes the fuel tank level sensor?

If so what is the new fuel gauges input range in terms of voltage?

BigDog

 

[Plateau]

Hello Big, are you fine?

First of all sorry for the unclear explanation about my problem. I will make a video explaining so much better.

You have replaced the fuel gauge in your vehicle and the new fuel gauges specs significantly differ for the original. Correct?

I have replaced the old analog dashboard for a new digital dashboard. My car is a Chevrolet Kadett (In USA is the same of Pontiac LeMans and UK is the same of Vauxhall Astra, do you know?)

The old dashboard:


The new dashboard:


The old and current fuel tank level sensor is a variable resistor actuated by a float where 0 Ohms representing empty tank and 90 Ohms representing full tank.

The new dashboard needs a fuel tank level sensor that give us 44 Ohms when the tank is full and 290 Ohms when the tank is empty

Do these fuel gauges display the fuel level based on an inputted voltage level derived from a resistive voltage divider which includes the fuel tank level sensor?

The new dashboard calculate the level of fuel using a voltage divider wich includes a 50 Ohms permanent resistor and the fuel tank level sensor... and the voltage input is 10v.
The least value of voltage should be 4,86v ((44/(44 + 50))*10v) and the highest should be 8,52v ((290/(290 + 50))*10v)

The PIC give us a value of resistence according to the value of voltage read from a voltage divider wich include the old fuel tank level sensor (0 ~ 90 Ohms) and a 100 Ohms permanent resistor and the voltage input is 5v.

Well... when I measure the value of the resulting resistence with the multimeter all the things is ok, but when I tried to make a voltage divider with this resulting resistence the ouput voltage is always lower than 6v.

Is there still any doubt?

Thanks for helping me,

Regards,

Pedro Rosa!

 

[Plateau]

As I have promised

Recording.WMV - YouTube