MAV-blog

Stuff related to MAV's (and UAV's) from a hobbyist's point of view. Info

New inertial sensor

Analog devices has created a new inertial sensor, the ADIS16355. It includes a 3 axis high precision gyroscope, and 3 accelerometers. On top of that, it includes digital I/O with some on-board basic sensor filtering. It’s target market are dead-reckoning applications such as car navigation when a GPS signal is lost.

Being a cube with a side of 23mm, it seems kind of big. Unfortunately no weight specs on the datasheet yet. For the very small MAV’s this might be too big, but for most autopilot systems this sensor will improve navigation performance!
Samples will cost $350, +1000 will be $250 per unit.

4 July 2007, 16:23 | Link | Comments [2]

Connecting a GPS (EB-85) to a PIC microcontroller

Last month I finally bought a GPS module. I decided on the EB-85 because it’s cheap (thanks to mr. rc-cam!) and it has a 5Hz update rate!

However, this module has an UART that operates at 2.8V. My PIC runs at 5V. After some investigations I figures out that the TTL pins of my PIC would interprete the 2.8V as logical high, but the ST-pins (Schmitt-trigger) won’t. Because the hardware UART or PIC uses ST, I was left with 2 options: Use the TTL-pins and a software UART or continue looking for another solution :-)

What I need is a TTL chip that has en open-collector output. TTL accepts 2.8V as a logical high, and the open-collector port allows me to use any voltage as logical out if I use a pull-up resistor.
My solution uses the 7407 IC, which is a “Hex Buffers/Drivers With Open-Collector High-Voltage Outputs”.

This is the schematic:

On the left you see the PIC, on the right you see the connector to my GPS. In the center-top you see the pull-up resistor to 5V, in the center-bottom you see the pull-up resistor to 2.8V that consists of a voltage divider that yields 2.8V.

On my test-board it looks as follows:

This is what my test-program does:

  1. Startup
  2. Send a message to the GPS so only the RMC (Recommanded minimum) messages come through:
$PMTK314,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0*29\r\n
  1. Every time a byte is received on the UART, an interrupt is launched and the received data is decoded.
  2. The main loop prints the data in the LCD

The overhead of the UART and GPS decoding is very low on my 4Mhz PIC. Perfect!

Here are some nice sites for electronics newbies like myself:

Update:
There was a slight error in my schematic: I played the voltage divider before the buffer instead of after it. It is corrected now.
This should also work (but my 7407 chip has 6 buffers so I didn’t care):

30 June 2007, 15:25 | Link | Comments [11]

Extremely basic autopilot

I found an interesting link while surfing the net (well, doesn’t it always happen like this ;-) )

It’s a rudder-driven autopilot with waypoints hard coded, but works with a PIC16F877
Very basic, but comes with pic-code and a very simple circuit.
http://www.pages.drexel.edu/~weg22/gpsMagpie/gpsFixedWing.html
Interesting to read.

23 June 2007, 07:08 | Link | Comments

FPV!

I was lucky enough to use someones wireless camera for two days. So I put it in my easy glider an HOP in the air with it! The transmitter was a 10mW one, and together with the CCD camera the imagery was brilliant!

The camera and transmitter I used is this one
The original quality was obviously a lot better than this compressed youtube one

20 April 2007, 14:59 | Link | Comments

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