Need mount for Freescale differential pressure sensor

[petespaco]

I'm new to arduino. I intend to build a process controller for a wood chip gasification system that supplies fuel gas (CO and H2)to a 60 KW genset that will be connected to the electric grid on a "net metering" contract.
To that end, I need to measure 4 pressures in the range of =/- 10 inches wc. Finding sensors to do this at a reasonable (to me) price is hard to do. But I HAVE found some. To be exact, the Freescale MPXV7007DP.
My problem(s):

1. I have looked at a LOT of Arduino examples and have found almost NONE that use pressure transducers other than barometric sensors.
---It's just interesting that folks don't seem to be interested in such things.
Is there some special place I should go?

2.The above mentioned sensor is an 8 pin surface mount looking device, but it has 0.1" pin spacing, like a old "DIP" chip, only wider, and with "flat feet" for soldering to pads. I can't find any kind of adapter board to use so I can plug it into a breadboard. The manufacturer says it's a DIP-8 case, but it isn't. It's a DIP-32 case.
I can't find any adapter boards that fit because this DIP-32 size is wider than DIP-8
What am I missing here?

If I get no replies, I will try to straighten out the "flat feet" and stick them into the breadboard, if they are long enough.

Pete
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[adafruit_support_mike]

The packages with the .05" pin spacing are the SOT family, and the number at the end tells you how many pins the device has. A surface-mount 555 chip comes in a SOT-8 package, for instance.

When you get into devices that have mechanical parts, like this one, the standard chip profiles and pin spacings don't apply. You just need to look at the recommended footprint pattern in the datasheet.

Since this device has pins on .1" centers, your best bet will probably be to get a chunk of prototyping board with copper pads around the holes and solder the device to that. Then cut chunks of 18 gauge wire about 3/4" long, bend them 90 degrees at one end so the long leg passes through one hole and the short leg reaches the next pad over. Put those in the protoboard so the short leg is soldered to the same pad as the device's pin, and the long leg is soldered to the next hole out.

As an alternative to hard pins, you might try using pieces of insulated 22-24 gauge wire about 3" long. You can plug the wires into your breadboard where you need them, instead of plugging the pins straight into the breadboard and then using jumpers.

[adafruit_support_bill]

I use a lot of the Freescale MPX series for various pressure applications. With .5 - 4.5v output, they are trivial to interface with an Arduino. And, the output is linear throughout the range, so no linearization curve is required. What is your application?

[CharlieD]

have a google at the Motorola range of sensors - there are some there which are mechanically far easier to mount, and the interface is the same as the freescale one you referenced

[petespaco]

I am interested in differential pressures in the +/- 2Kpa and +/- 7Kpa range for now. We're talking 0.3 psi to a max of about 1 psi. I am really measuring values in the 1 inch WC to about 10 or 12 inches WC range. And I need to be able to differentiate between -1" WC and -2" wc. Primarily measuring suction through my gasifier and its filter system as incoming air and llater,the gas moves through. It's a bit complicated since the gas is boosted with a blower on its way to the engine's intake. (See my original post). The incoming air is at ambient temp, at the output of the reactor, it can get as hot as about 1500 degrees F. The gases cool in the filter but can get pretty wet part way through.

And yes, I have looked at some of the Motorola sensors. I think I saw one style that is a disc shape, standing on end, with ports sticking straight up. I may look again, but I think the ones I need start at somewhere between $30 or $40 each, where the Freescale sensors I need are about $12.

As you guys probably know, one of the mounting and connection issues with the Freescale sensors is that the lower barb on the differential sensor actually sits a tiny bit BELOW the level of the PCB that it would sit on, so it has to be mounted right at the edge of a board. This means the legs go the wrong way for premade boards. Not tooooo big a deal; I'll just do as adafruit support suggested, but cut the boards up as needed to get connection clearance.
I 'spose I could start making boards, but my main project is woodgas to electricity, pcb mfg.

It's not MY fault for going on so long; it's YOUR fault for getting me on my favorite subject!

Thanks for your comments, guys. I always learn.
Pete
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[petespaco]

Thanks for all the input so far, folks.
I have built breakout boards for 4 MPXV series differential pressure sensors, 2 ea. 7007 and 2 ea. 7002.
They work. By having each sensor on a separate board, I can plug them in as needed.
Currently, I have a 20 X 4 LCD, 2 Max6675's, 2 LEDS, a thermistor, SD breakout board, and one Freescale MPXV7007DP hooked to my ATMega2560, powered from the USB cable.

New question 1.
Pressure sensor Calibration:
I read this article over and over. This isn't the same sensor that I am using, but I thought there'd be a lot of similarity:
http://spiffie.org/electronics/archives ... nsors.html

But the resolution and calibration seems a lot more complex than what I SEEM to need. I didn't do any of the reference setting that is described in this article and couldn't find reference to it in the datasheets for the sensors I am using. What am I missing?
Have the products changed since about 2009? When I fire up my circuit, I get a "0" reading every time. I just "map" to get a 1/4"wc resolution and divide by two for an offset to get into the middle since these are differential pressure sensors. I just chose a "map" range that gets me the resolution I need, while giving me the full scale limits of the sensor.

New Question 2.
I am new to Arduino, so I am borrowing code from everywhere. Right now my "root" program is an assemblage of at least a half dozen others. One of those programs does some sort of reference voltage calculation and then prints the result to the SD card and to the serial monitor.
Here's the first part of it:
//Code to prepare reference voltage to read and log
#define BANDGAPREF 14 // special indicator that we want to measure the bandgap
#define aref_voltage 3.3 // we tie 3.3V to ARef and measure it with a multimeter!
#define bandgap_voltage 1.1 // this is not super guaranteed but its not -too- off
-----------------------------------
Here's the rest of it:
// Log the estimated 'VCC' voltage by measuring the internal 1.1v ref
analogRead(BANDGAPREF);
delay(10);
int refReading = analogRead(BANDGAPREF);
float supplyvoltage = (bandgap_voltage * 1024) / refReading;

logfile.print(", ");
logfile.print(supplyvoltage);
#if ECHO_TO_SERIAL
Serial.print(", ");
Serial.print(supplyvoltage);
#endif // ECHO_TO_SERIAL

logfile.println();
#if ECHO_TO_SERIAL
Serial.println();
----------------------------------------
The number it prints is in the range of 2.5 volts and seems to vary from about 2.48 to 2.6 over many hours.
I have noted, however, that, when I vary the pressure to a sensor, that voltage drops to as low as about 2.25 volts.
---Does this mean that the Freescale sensor is taking a lot of current to do its thing?
---And, more importantly is this affecting the accuracy of my readings? ---Maybe the linearity?
---Finally, is it time to plug the 9 volt wall wart into my ATMega2560? (I have avoided doing this cuss I don't want to blow anything up!)

Pete Stanaitis
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