zVMAP

Each VMAP is individually calibrated to replicate a Bosch 2.5 ... 3.0 bar sensor and the precision equivalents. We went to great lengths to accomplish this and make it very accurate over the entire temperature range. Also - if you pay a little extra you can have one that is adjustable from 2.5 to 4.0 bar in 0.1 bar steps. I run mine at 2.9 bar with 91 octane in the car.

There are 2 main variables one has to be concerned about (we won't go into the third and forth) and the circuit that is shown later attempts to address gain but will exhibit a very inaccurate offset. (Also don't forget op Amps make good oscillators if they are not laid out and compensated correctly ... so know what you are doing). With the adjustment of the values of the Bosch 2.5 bar sensors it is highly unlikely that you will replicate a Bosch 3.0 bar sensor and again what have you done for the reliability of that sensor? In Mihneas case he has the ability to adjust for these inaccuracies during his tuning session.

If you really want it cheaper buy a new GM Sensor and run the wires external. The MPX6300A curve does not replicate a Bosch sensor nor does a GM sensor ... however the GM sensor is closer to the Bosch characteristics.

Again it all depends what you want. If you want the best with years of proven reliability and accuracy go with a VMAP or with 0 features Bosch 3.0 bar. I hear the Bosch 3.0 bars are $300.00 - 400.00+ now ... so who knows if the VMAP pricing will stay so low?

Best regards,
Feico van der Laan

zVMAP

At fist glance it sure would be nice if it could be done with such a simple amplifier circuit and in a perfect world it could ... maybe this 750 kPa sensor is perfect ... however the 700 kPa MPX5700 you refer to is not!

This is a simple gain stage of about 2.33 when set to 3.0 bar and there is no offset compensation at all.

If there is a 0.2 volts offset which is typical for a production MAP sensor the error is as large as 0.2 * 2.33 = 0.47 volts. In addition these offset values can have a maximum deviation in excess of 0.4 volts providing an offset error of at least 0.4 * 2.33 = 0.932 volts!!!!

Not acceptable at all in my car.

At 1 bar absolute the ECU expects a signal around 1.5 volts. With this circuit the ECU may be getting a signal as high as as 1.97 volts in a TYPICAL case and 2.43 volts in the worst case.

This is equivalent to providing the ECU with an output of 1.31 bar absolute in a typical case or 1.62 bar in a worst case scenario when it expects 1.0 bar. Anything more than 1.1 bar is probably unacceptable in most cases.

Best regards,
Feico van der Laan

zVMAP

The MPX5700 has an offset as high as 0.409 volts and a gain error of +/- 2.5%.

Your circuit has 0 offset compensation and no gain fine tuning. Yikes! Although a fine attempt if it had 0 offset.

See later post about a not so perfect world!

Best regards,
Feico van der Laan

zVMAP

Kevin,

Knowing how accurate you are with the TDS-1 ... I know you would find the offset error unacceptable with this circuit. See earlier post.

This circuit has 0 offset corrections. Even worse it acts as an offset multiplier.

Does it work ... yes ... is it grossly inaccurate ...yes.

The specs are the specs. This circuit does nothing with respect to error compensation for the MAPs short comings. Actually it multiplies them.

Best regards,
Feico van der Laan

kday

There is a bit of unwritten back story here, in that Marc is looking for a way to run his TDS-1 now that he has gone standalone. I think you'd probably agree that using a VMAP just to drive the TDS-1 might not be cost-justified in all cases. It seems more accurate than necessary just for instrumentation. It is certainly the easist and most accurate way, though.

I agree with your points regarding the scaled MPX part as a replacement for the MAP in the Motronic. I wouldn't do that myself, although as you say, with custom tuning it can probably be compensated for to some extent (+/- ambient temp, etc.)

a4kquattro

as Kevin pointed out in a later post, I dont even run motronic anymore on my car and was just curious about what options I have to make use of my TDS-1 (you should get one by the way, great product!)

The VMAP is an excellent solution.

sergeynik s6

This scheme - sketches before work. Shift 0 has been compensated by diodes.