Freescale/Motorola Pressure Transducer

[salvageV6]

Here is a link to a $16 pressure transducer which reads 0 to 36 psi. gauge pressure.

The output is approx. 0 to 5V specs. are at Newark electronics link pages.

From that using a voltage comparator approx. $3 or less we can build pressure switches, readouts for LED's, boost shift lights etc.

Circuits and instructions to follow............

http://www.newark.com/freescale-sem...ensor-0-to-250kpa/dp/48F4498?in_merch=Popular Products

 

[davelostmissing]

Xenocron have had had kits using MPX variants for a long time- even hiding them inside the OEM sensors.

I don't doubt that's what is inside many OEMS

 

[salvageV6]

Here is some pics. of the schematic for the basic building block of the system.

Easy to source parts (Radio Shack, any Electronic distributor etc.) capacitors and the MPX4250GP from Newark Electronics.

Radio Shack has the 5V regultors you can use the 100ma version or the 1A version in the TO220 package and buy a heat sink for it cheap enough although the current will never approach 1A from the 5V source.

After building this portion of the circuit you simply attach well regulated shop air from 0 to 36 psi. and make a chart of the voltage output from the system over each 1/2 psi.

That will give you the target voltages you need to match for the comparator circuit to be added next.

 

[davelostmissing]

Good.
I think the 78L05 is plenty here. The individual calibration deals with the ratiomatic nature of the sensors and regulator variance. Considered something more on the input for transients, load-dumps? An insulated tab like a NJM7805FA might be good for "breadboarders"?

 

[salvageV6]

I stick my breadboards in a cheesy plastic box, it's small enough to fit anywhere, use some small 1/4" standoffs for #6 or 4-40 screws to mount it.

Same with the MPX4250GP to the breadboard locate it so the nipple sticks out a 1/2" or so hole.

Cut the hole in the side of the box and attach your choice of hose to the nipple using a clamp or super glue/hairspray.

The 5V signal is plenty stable especially with the basic filtering.

Next up is the LM339 comparator and some reference voltages you can set to trigger at different psi. outputs.

The 339 can drive high brightness LED's decently but we can add a transistor switch to control relay coils to trigger things like an alky. solenoid to add nozzles at higher boost or open a direct line to a wastegate if overboost is detected etc. etc. etc.

 

[TurboDave]

Stupid question, maybe I'm missing something. Why do you keep calling it a 0-36psi device when it's called out on the spec sheet as 0-250kpa?? 250kpa is only about 21psi if I recall correctly.

 

[salvageV6]

It's gauge pressure there's no need to read atmosphere for what we're doing here.

We only care about boost pressure above atmosphere here.

Just add 14 or so atmospheric psi. and voila 36psi.