Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Pressure sensor on a Pic

Status
Not open for further replies.

brentonw2004

New Member
Hello Everyone! I am trying to build a digital boost gauge for automobiles. I am using a Pic 16F876, a 16x2 HD44780 LCD, and this pressure sensor:

http://catalog.sensing.honeywell.com/datasheet.asp?FAM=Pressure&PN=24PCDFA6G

For anyone here who has helped me with the rest of my project, I have finally gotten my LCD to work with my Pic, and have gotten serial communication, so thanks! The only thing that I have to figure out is how to get the pressure sensor to work with the Pic. There are four pins on the pressure sensor. 1->+V, 2->Output+, 3->GND, 4->Output- . I am supplying it with +5V and GND. I am then sending my + & - output to the An0, and An1 port of the Pic. I checked both of their values with a meter and one was 2.53V and the other was 2.54V. This is not nearly enough of a difference to measure. I need to have one output voltage with 0v being -30 psi, and 5v being +30psi. I think I need some type of differential amplifier for my circuit. If anyone has a schematic or advice on building a differential amplifier that can let me measure both boost and vacuum pressure I would definitely appreciate it. Does anyone know of any sites with an example of using a sensor such as this? Any type of advice is welcome. Thanks!
 
As i see this is also a bridge-type sensor as Motorola similar device. You need some amplifier like this:
 

Attachments

  • MPX_207.jpg
    MPX_207.jpg
    24.1 KB · Views: 1,399
What exactly is the MC33274? I take that it is a quad differential amplifier. Where can I find one of these? Does anyone have any experience with these? Can I find one of these at RadioShack? I don't want to pay 6 dollars shipping for a 1 dollar piece. Any advice is welcome.
 
Also, what type of voltages do I need to operate this chip? I know that most op amps work on +-18V, but i am working off of a +5v for the pic controller, or the unregulated vehicle voltage. How would I obtain the +-18V from a car power supply? Schematics are very welcome.
Thanks!
Brent
 
Sorry about this, but I have one more question. How do you have to adjust the amount that the amplifier amplifies the signal? Sorry about my ignorance.
Thanks!
 
This should do what you want. I used a current source to excite the bridge, since the datasheet says that this makes it self-compensating. You can tweak the current with RV1 to calibrate the full scale pressure(basically a gain adjustment), if you have a way to calibrate it. Otherwise, just set RV1 to half scale. Adjust RV2 to set the output to half scale (+2.5v if you have a 5v reference on your A/D converter) with zero differential (atmospheric) pressure.
You should try to use 1% resistors (not the pots) for good temperature stability of offset, gain, and common-mode rejection. They are not expensive, but may be hard to find locally.
 

Attachments

  • bridge_amp_111.gif
    bridge_amp_111.gif
    10.4 KB · Views: 885
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top