Pressure Sensor

NWCCTV

I have a couple questions about the Pressure Sensor in the Micro Medic kit. First, after following the instructions here: http://learn.parallax.com/pressure-sensor-bar-graph-propeller-spin-demo My reading is at 325 to 326 and it shows only 44. Is this correct? Next, if I connect a hose to one end and blow on it is the data suppose to change or what? Edit: Now I see what I did wrong. I had the ADC on 3 instead of 0. I see that when putting air through it the numbers go up and the rest of the LED's light up. Quite cool and I think this is what I need for a portion of my project!!!

GrandeNurse

now that you have it running, how do you plan on calibrating it? If you are using this with the Blood Pressure cuff, you can read the (I hope this meter is still calibrated after I dropped it on the ground) meter and correlate the values. But do the values change per day (humidity, temperature, vibrations, ...)? When you determine the reading is 120 mm hg, how precise / accurate is it ?

frank freedman

Having the device able to determine a pressure is only one part of the equation for BP readings. You will still need to be able to detect the Korotkoff sounds in order to determine the correct systolic and diastolic pressure values. Better to probably hack a Walmart personal BP device to get this value. They are probably more stable than the PCT using the stethoscope who may have a cold or allergies causing hearing level differences day to day. Course you would then have a working system to dissect and analyse including the pressure and sound sensors as well as the display.

Personally if I had the time I dream of this device could be the centerpiece for a good pulmonary measurement and therapy system as a flow/volume meter in differential mode. Add in a CO2 sensor and other possibilities open up.........

GrandeNurse

Patient care technicians (PCT), Certified Nursing Assistants (CNA), Nurse (LPN, RN), Doctor ……, all of them can get different values on the same patient, just like the equipment. I’ve also seen automated machines get different results due to cuff placement or vibrations on the air hose. Multiple readings sound good, so the average could be recorded, but they also have issues.

Is it the operator / machine or could it be tissue issues? Performing a Blood Pressure on a patient may force absorption of fluids into cells due to an increased differential pressure, so additional readings performed in the next several minutes end up with slightly different results.

“Gauge” readings are suppose to be compensated but seem to be subject to variations in room/tube-bend pressure. A true Hg U-tube is already compensated to atmospheric pressure and has enough mass to reduce vibration issues. What about a sensor array on an Hg U-tube for comparison values to your pressure sensor?

NWCCTV

So, I was able to get everything working in the Demo code for the Pressure Sensor. The Bar Graph Lights go on up the bar when pressure goes up and they go back down when the pressure goes down. Also, the Serial Terminal shows the increase and decrease. I was also able to edit the program using dira and outa to light up the LED on pin 11 if the pressure >= 150. Now I am stuck. I just want to be able to modify the Pressure Sensor Demo code to be able to start turning a Servo clockwise when the pressure is >= 150 instead of lighting the LED. I have tried various ways of doing this and nothing seems to work. I tried to create a new Cog and that did not help. I just want the servo to turn without having to write 100 plus lines of code to do it. This would be so much easier if it were in PBasic. @xanadu posted what he thought would work here: http://forums.parallax.com/showthread.php/147086-Spin-Help-Needed but even using the OBEX he suggested I am getting errors as outlined in tht thread. I thought I would post here since there may be more people interested in this Forum that are working with the same sensor.

frank freedman

If this is for a BP cuff, is there a reason you need a servo to work? One of the major OEMs uses a dc motorized pump to inflate the cuff. Near as I can tell without access to the code, the solenoid valves close and the motor is turned on. Since the systolic pressures can cover a wide range, you may want to consider the point where the appropriate korotkoff sounds are detected + maybe a percentage beyond that. I believe that is what this OEM does. Once that pressure is reached, one of the solenoid valves opens to let the air out at a slow enough rate to detect the sounds on the way down and records the pressure at least the points indicating again the systolic pressure followed by I think the point of no further sound (which some references consider an appropriate point to record the diastolic pressure) and then open the large valve to dump the remaining pressure. I think the big valve (or they could be two smaller valves open at the same time) is also used to dump pressure in a failure/error condition.

NWCCTV

No, It is not for a BP cuff. I am going a completely different direction with this sensor and yes there is a reason I need the servo to turn. Otherwise I would not be wasting my time with it.

NWCCTV

OK. For anyone that might need to start a servo when your pressure sensor gets to a specific rawReading I have modified the Pressure Sensor Demo code to do just that. You may think it is not a big deal but being new to Spin it took me a week to figure this one out!!!! Why turn a servo using pressure sensor??? Stay tuned and that will be revealed when I finish my Contest project!!!!

frank freedman

Never said or implied time waste. Rough guess given what was in the kit. Other than that, merely curious regarding the final app.

Dat was all.

F

NWCCTV wrote: »

No, It is not for a BP cuff. I am going a completely different direction with this sensor and yes there is a reason I need the servo to turn. Otherwise I would not be wasting my time with it.