Arduino Based Boost/Pressure Gauge

[Lactard]

So a buddy of mine recently picked up a turbo for his car but does not have a boost gauge. So I thought about trying to build one.

What really makes this different from other gauges that can be found on the internet? You don't have to buy another sensor, no long complicated code, and its universal as long as you can figure out the "sensitivity".

MAP Sensor theory of operation
When ECU is powered on (IGN ON, ENG OFF), it reads the output voltage from the MAP sensor and sets that as a reference to compare against the pressure/vacuum in the manifold while the engine is running. I wrote a program based on that theory.

In a lot of forums I've read that out MAP sensor is rated @ 1.7Bar but I have never seen a reference noted of that information. So after digging I was able to find a parts catalog that contains the Operating Range I was looking for. FAE, a electronic spare parts manufacture in Barcelona, supplies manufactures from all over the world with sensors.

http://www.fae.es/catalogos/part_ilu...tualitzada.pdf

From that catalog, our MAP sensor operates between 10kPa to 160kPA. 160kPa == 1.6Bar == 23.2 PSI. Since Sea Level is about 14.7 PSI, mathematically, you have 8.5 PSI limit.

More math:
EP3 MAP sensor range
0.4V == 10kPa
4.65V == 165kPa

The formula in the catalog: Vout = (Sensitivity * Pressure in kPA) - Offset
Look familiar? Slope intercept, Y = MX + B. This shows that the MAP sensor is very linear and easy to calculate.

Plugging in the variables... there are still two unknown variables.
0.4V = (Sensitivity * 165kPa) - Offset

Because of its linearity, we can make Offset == 0.1. Now the equation looks like...
0.4V = (Sensitivity * 165kPa) - 0.1
Sensitivity = (0.4V - 0.1)/10kPa == 0.03, makes sense to solve for the high range.

Sensitivity = (4.65V - 0.1)/165kPa == 0.027575
Pretty close, 9% difference. To be safe, the average is 0.02878

Now you can easily calculate pressure for any output voltage from the MAP.
Pressure = (Vout - Offset)/Sensitivity
Sensitivity = 0.02878
Offset = 0.1

As far as the program goes, the bench results work exactly as the theory says. Just have to tap into the MAP output wire to see if it works in the real world.