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Altimeter circuit

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Hello,

I am thinking in building my own altimeter circuit and I was wondering if anyone of you already built this circuit? Which pressure sensor would you recommend ?

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I'v just built such a circuit.Using a motorola 4115,with an op.amp to limit the resolution to a theoretical 10k/ft. If you register with Freescale,I think thats what this division of Motorola call themselves now,you can get a couple of 4115's as samples for free!

You may also need a ADC,to interface a micro,if you want better than 10bits resolution.Try the Maxim 186(8 channel) or Maxim 187(Single channel) These can be obtained,also for free at the Maxim web site.

Just let me know if I can give you any more help.

Lyn. :D

Edited by Johnstorm

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Hello,

I must admit I am quite new in the electronics and micro-controllers world, and I have some troubles choosing the right component. From the Maxim's website, I see that the Max189 has an external voltage reference from 0 to 5V whereas the Max187 has a internal voltage reference of 4.096V. Can't I simply connect +5V to the ext voltage ref pin to get 0 -> +5V résolution on the max189 ?

Or do you know a 8051 core micro-controller with an ADC and a limited number of IO pins ?

Thank you for your help.

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Yes you can connect Ref to your 5v supply on the Max189,which does not have an internal reference,In fact this is the way it's done.As on the Max187,with internal reference you have to use either-internal reference, pull the Shdn pin high.Or float the Shdn pin(don't connect at all)to use your external 5v reference.If you order samples of the Max189,the one I am using,try to opt for the Max189AEPA (8 pin dip),or Max189AEWE (16 pin SMT).Check the downloadable spec sheet.

I personally have opted to use the Atmel AVR range of micro's.And for this particular project the Atmel Mega8,check them out!

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Or do you know a 8051 core micro-controller with an ADC and a limited number of IO pins ?

I personally have opted to use the Atmel AVR range of micro's.

The instruction sets are compatible.

A few project links here;

ULinks

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Hi Mike.

You'r right it does appear the 8051 architecture is compatable with the Atmel,so it makes sense the instruction sets would also be so.

Had a quick glance at the links! Nice one!

Lyn.

Edited by Johnstorm

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Thank you all for all your helpful information. But where did you see that avr instruction s set is compatible with 8051 ?

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Mikep was working on an altimeter project a while back.Unfortunately I have not seen any posts on this project,or indeed from Mike for a good while.

Lyn

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Sorry again for my ignorance, but what can substitute the MAX187 or MAX189 AD converter, because Farnell does not sell it... Actually I'm looking for a single channel 12-Bit serial AD converter...

Thank you again for your help!

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what can substitute the MAX187 or MAX189 AD converter, because Farnell does not sell it...

Maxim offers free IC samples. There is no need to spend a cent on these unless you need a lot of them.

http://www.maxim-ic.com/samples/index.cfm?...d&PartNo=MAX187

http://www.maxim-ic.com/samples/index.cfm?...d&PartNo=MAX189

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As I stated in my first reply,and Mr RC just said you can obtain these for free from Maxim's web site.Just register with them and be cheeky and ask for either,Max 189 AEPA 8 pin DIP,or Max189AEWE 16 pin SMT package.(A=lowest error,E=-40deg to 125deg temp.)

Lyn.

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I managed to get the mpx4114A pressure sensor working, using a max189 and a lm4040 (4.096) as a voltage reference. However, I still have a problem regarding the accuracy of these value : When the circuit is on my desk, I get value from 3997 (3.997V , 1mv resolution ) to 4003 when I expected to get the same value everytime. Is it normal that I don't get everytime the same value ?

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Do you mean it changes every few seconds or every few hours ?

It may be that you are measuring the change in air pressure where you are, you do now have a barometer !

Terry

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