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RE: [Paparazzi-devel] IR resister swap, power supply, and video telemetr

From: akochevar
Subject: RE: [Paparazzi-devel] IR resister swap, power supply, and video telemetry
Date: Wed, 21 Feb 2007 09:12:40 -0700
User-agent: Web-Based Email 4.9.18

Let me see if I can shed some light for you.
1.) First off we have been meaning to clarify this for some time just havent gotten around to it.  The FMA board was designed to run off a 5V input with a 2.5v nominal output on the signals of the sensors with this signal voltage moving up or down with heat.  The new autopilots run off of a 3.3v source, and the signals will be centered on 1.65v.  This all works with the FMA board.  The problem arises with the Gain of the analog system.  The gain of the FMA board is 2000 I believe(need to check exact values).  Set by 2 resistors, a 1Mohm and a 500ohm, 1,000,000/500 = 2000.  This gain needs to be lowered to about 3.3/5 of 2000, which would be 1300.  Because its just easier we swap the resistors with a 1K and set the gain to 1000.  If you dont change the gain the sensors can become saturated at a lower temperature(like flying in the summer here in tucson).  Now something in my math is fuzzy because I thought the gain we were trying for was 660, but anyways you get the point.  You have to do this to both channels(pitch and roll). 
2.)  I dont see why you couldnt do this, and just tap the motor battery voltage to the ADC channel so you could monitor it.  The Tiny has a voltage regulator so you could bypass it if youw anted to use a nicad pack(5vish), but only the servos run off this voltage, everything else is 3.3v.  With a nice switching regulator we didnt see a need to seperate the batteries.  This is nice to have when you dont know the voltage, so if the motor cuts off you still have avionics, but when you know the voltage you can land safely long before the battery dies.  A second pack seems overkill?
3.)  Ok here is the deal with modems and video.  Most modem systems are on 900Mhz while video is on 2.4Ghz.  Some users are using hte Xbee modems from Maxstream which are 2.4Ghz and 100mw, these are nice units for testing and are really cheap(40 bucks a piece).  They have limited range that is really affected by where you fly(nearby wifi connections).  They will also step on any 2.4 video system.  The 900Mhz modems like the 9xtend from Maxstream are higher power longer range more expensive and heavier.  we have flown out a long way with these.  Audio telemetry is all but dead.  The Tiny 1.1 does not even have the hardware to do the audio encoding to be sent down the video transmitter.  Some people still use it(the University of Arizona) but they are even gettign rid of it.  The ability to move waypoints on the map, change any gain, update the flight altitude, are all thi ngs you can do with a modem that you cant with just audio downlink(because its unidirectional).  Hmm I think thats it.  Let us know if you have any other questions. 
Questions like these are perfect for the mailing list because it allows people to see the answers, when you get to building and have up to the minute questions go ahead and stop by #paparazzi on freenodes and ask there.
Anton Kochevar

-------- Original Message --------
Subject: [Paparazzi-devel] IR resister swap, power supply, and video
From: "John Koches" <address@hidden>
Date: Wed, February 21, 2007 7:54 am
To: <address@hidden>

We are moving along on our project, but I have some questions.
1.  I purchased the ready made FMA Direct IR Sensor.  Before I go opening up the case, the website ( ) indicates that a "simple resister swap" is all that is required to make this device workable.  I assume you are talking about the sensor board.  Could you elaborate please.
2.  The general diagram showing the Tiny 13 v1.1 board ( )  indicates that the flight battery is split between the board and the ESC.  I assume you are talking about a y connection and not two separate batteries so that you can monitor voltage as part of your system operations.  Is this correct?  Is there a reason that I couldn't use two batteries and keep the motor systems separate?  Are there any advantages to this solution?  I realize that we are talking more weight now.
3.  I am confused regarding the need for modem and/or video transmitter.  It sounds like if you can live without a video camera, you can install a modem for data telemetry.  But if you want a video camera, you need to find a video transmitter that handles audio so that you can send telemetry down that side of the system.  I suppose you could have a separate video system with flight telemetry going through the Auto Pilot using both a modem and a video transmitter, but I don't think that is what is intended.  Like I said, I am a little confused and I just need some clarification before I start the development of my ground station.
Thanks in advance for your help.

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