Reading a Mass air flow meter

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

Hi All,

Got a puzzling mystery for someone with better understanding of electronics than me. I am trying to read an automotive mass air flow meter with arduino nano. I have it setup as follows.

Arduino + and - come from the car ECU's regulated 5v output.

The MAF meter hot film needs 12v and the device outputs a 0-5v signal to indicate mass flow.

The 12v to the MAF hot film is supplied via the battery + and -.

The - of the MAF output is connected to gnd on arduino and the + of the output is connected to analogue input 4.

Here is the problem. When the connection from the ECU is unplugged and the arduino has no connection to GND or 5v, the voltage across the MAF sensor output is correct about 0.2v with no flow. When I plug the arduino in I measure about 2.7v across the MAF output with no flow. Im not sure what is causing this. Any ideas? I would imagine its no coincident that its shifted by half of 5v.

Tom

2

it sounds like your circuit is probably loading the circuit under test, and thus affecting the measurement.

have you considered using the OBDII connector inside the passenger compartment, and querying the automobile's central computer for the sensor data?

3

The vehicle in question pre-dates such things. Wouldn't loading the circuit cause a voltage drop rather than an increase? Where do you think a load might be coming from, the output is only connected to ground and an analogue input.

4

All sorted now, had the sensor output wired the wrong way round :D.

5

Hi there,

I am interested to know which mass air flow meter you are using :slight_smile:

I've seen this used to balance carbs - using an Arduino to go with a display would work really well.

James

6

Its a bosch hot film sensor. I can't remember the exact one but I will post it when I get home.

7

cool - could you let me know the pin outs also?

all useful if someone has done it before :slight_smile:

8

Ill go one better and link you to the datasheet.

9

Sounds great!

10
11

that datasheet is for a 4 pin - but you seem to be describing one with more pins?