# Thread: Unsure what area this relates to but im struggling with an ignition map

1. ## Unsure what area this relates to but im struggling with an ignition map

Im trying to write a microcontroller program to run the ignition in my car.

However im struggling to interpret values from a table properly if the value i need falls inbetween the values in the table, im not convinced the method im using does a very good job.

Going by the image i have attached what would be the value for advance be if the load was 67 and the RPM was 4600?

thanks

Dan

2. Originally Posted by powermandan
Im trying to write a microcontroller program to run the ignition in my car.

However im struggling to interpret values from a table properly if the value i need falls inbetween the values in the table, im not convinced the method im using does a very good job.

Going by the image i have attached what would be the value for advance be if the load was 67 and the RPM was 4600?

thanks

Dan
Linear interpolation:

1. Assume that the increase between 60 and 80 or 4000 and 5000 respectively is proprtional. That means: To reach the 67 you have to calculate: $67 = 60+(80-60) \cdot \frac{7}{80-60}$. So the increase is $\frac7{20}$ of the difference of the 2 corresponding values.
Now calculate the 2 values in the 4000 and 5000 column.

2. The increase in the last row is $\frac{600}{1000} = 0.6$ of the difference between the 2 corresponding values in the last row.

3. Now calculate the increase between the newly calculated values.

4. I've attached a table with the results.

3. Thank you very much