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Attention: RC-CAM.com will be closing down August 2021.

The RC-Cam.com forum was the very first online community dedicated to the advancement of wireless video cameras on radio controlled (R/C) models. This is now called "FPV" (First Person View). We are proud of the contributions that our members have made to the FPV hobby.

We've seen significant changes over the last twenty years. Initially there were a lot of eager R/C hobbyist that built their own video systems. Allowing these creative individuals to share their work was the purpose of this site. Now the FPV market is flooded with low cost systems; Sadly DiY FPV video projects are now rarely discussed.

RC-CAM.com (main site and forum) will be closing down August 2021. This is being announced now (March 2021) so that everyone has time to download any information that is important to them. After the site is shutdown the information will no longer be available here.

We appreciate every member's involvement with advancing the FPV hobby. It is indeed sad to say goodbye to all our online friends. Be safe and stay healthy.

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Can you give me a part name I can use as a 5V precision VRef ?

I just realized I had a brain fart. The MPX does not utilize external Vref (it can only create it internally). So, despite the hope I offered by suggesting a better part than the LM7805, it probably won't help you much to change it. You didn't say what your latest temperature drift results were (with amp removed), or how the test was performed, but it could very well reflect the basic performance of the design.

By the way, what do you use to power the circuit?

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With op amp removed , I also get the drift curve.

I made another test , I connected a battery to the op amp input , instead of the MPX pressure sensor. I also get a drif.

So resistors and mpx may not cause the problem . I can be either the 7805 or the ADC.

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Reducing the circuit to a minimum configuration is a good plan. If the latest configuration has drift that is temperature related, what temperature extremes are you testing with? What does the latest test circuit look like?

Keep in mind that batteries are temperature sensitive too. So, don't let that skew the results. :) As mentioned, you can carefully direct warm air from a hair dryer to test the reaction of each part. That way you can find those that are the worst offenders. But, you will probably never totally eliminate the issue -- all you can do is work within the component specifications.

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  • 2 weeks later...


I've rebuild the circuit, changing some resistors value and I still have a drift but less than the previous version. Anyway I think this will be ok for now. This project was fun at beginning but now I want to move to something else ;)


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I've started using Eagle to make the schematic and the board. My aim is to make a little PCB for this altimeter and thus, learn the process of board making. My problem is I don't know if the PCB eagle generate is correct. Can you have a little look at it and eventually tell me the mistakes I made ?

I also think I messed up something with vdd/vss/vdd/gnd in the schematic. In eagle, do you use the auto route feature? If I use it, can I be sure that the board connections match the schematics connection ?

I attached the board and the schematic file.


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I can't view the rar file. But, here are some things to consider in making your first PCB:

(1) Do not autoroute until you are good at manual routing.

(2) Pay close attention to how you run your power and gnds in this circuit, otherwise you will introduce noise in the analog path. That is, do not share digital power and digital gnd with analog power and analog gnd. They should be separate busses, with common connections at your power supply.

(3) Make sure your decoupling caps are very close to the IC's.

(4) Size the trace width to handle the current. Do not use fine widths (under 12mil) unless you know your fab vendor will accept them. As a general rule , avoid sharp 90 degree corners (bevel route them).

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