|Oct 26, 2013, 10:41 AM|
RSSI tracker Arduino based
The incentive to build the Arduino based rssi tracker came after building a transistor based one and working with it for a while. It would do a good job of pointing at the model but was a difficult to get tuned, slow to find the model, and constantly moving back and forth when in use. I made a “wish”list of the things that I would improve. Most important it needed to have a LCD screen so I could see what I was adjusting in “numbers”. I presented my idea to a longtime friend “Eric”, he programs computers for a living and is also a modeler, not FPV “yet”. Eric has been able to implement all of my ideas and added a few of his own. What we have created IMHO is a giant improvement to the analog rssi design.
The processor based circuit can process so much information in a very short time that it is possible to read the RSSI values from the tracking receivers, filter out the erroneous readings, average the ones left and determine which direction to move the servo to keep the signals balanced in the middle. All this occurs about 60 times per second. I chose to use a servo as the drive motor but bypass the onboard servo control board. The servo is controlled from a separate motor driver giving it a linear ramp of the speed. If code determines that the error between the two receivers is excessive it will ramp the motor to high speed, about 120 degrees / second, and very quickly zero in on the model. The turntable design is not too critical as long as it is capable of full speed rotation of about 360 degrees in 3 seconds.
(1) LCD, these can be found all over EBay. Referred to as; 16x2 character LCD display module, HD44780 controller. They come in different backlight colors, I chose yellow.
(1) Serial interface for the LCD. This interface allows the Arduino to communicate with the LCD using only 2 IO connections. Referred to as I2C/TWI/SPI Serial Interface Board Module for 1602LCD Display.
(1) Motor controller; http://www.pololu.com/product/1212
(1) Arduino Pro Mini 328 - 5V/16MHz https://www.sparkfun.com/products/11113
These can be found on Ebay for $6.50 but be sure they are the current design with A4-A7 connections.
(1) Slip ring, 12 circuit 22mm
(1) standard size servo, speed @ 5 volts .10 - .18 sec / 60 degrees, prefer ball bearings and metal output shaft but not mandatory.
(3) RC305 receivers, modified for RSSI output, see method below.
(2) tracking antennas, I prefer 5 turn helical, but others may also work good.
(1) receiving antenna I am using a 3 turn helical but anything should work here.
(1) mini toggle switch.
(1) 3000uf or larger 15V capacitor, this one is 4200uf and the same physical size as the 3000uf. http://www.mouser.com/Search/Product...BG250ELL422AM2
(2) 7805 regulator.
(3) push button switches. https://www.sparkfun.com/products/97
(1) 4.7K (472) SMD resistor
(1) 10K (103) SMD resistor
(3) 2.2K (222) SMD resistor
(4) 1N40## SMD diodes, these can be 1N4001 – 1N4007 as long as they are rated at 1 amp. I used these. http://www.mouser.com/Search/Product...y511-STTH102AY
(2) 10uf 10V SMD capacitors
(3) .047uf (473) ceramic
I did not include in the parts list the bolts & nuts, header pins, connectors, circuit board material, interconnecting wire, etc.
The tracker needs to use the RSSI signals from the two outside receivers so they must be modified as in the picture. It is not necessary to modify the center receiver. To make it simple to plug into the tracker board I used a servo wire/plug and incorporated the power and RSSI into that cable.
It is important to use the 10K ohm resistor to protect the RSSI pin on the receiver. Without the resistor it the pin were ever grounded while power is on the RSSI circuit will be destroyed. The receiver will still output video and audio but not RSSI.
|Oct 26, 2013, 10:59 AM|
I would be interested in seeing your servo driver.
I have allot of ongoing work happening in relation to exactly the same project.
I even have a chap who has all the CNC equipment on board to help make a suitable chassis for a pan and tilt mechanism :)
For your filtering.. I spent allot of time testing for bad data on the rssi signal. Tried various filters... And in the end have gone back to unfiltered. I found it worked better!
Maybe just my algorithms that where dodgy :)
|Oct 26, 2013, 11:20 AM|
This is the design. It is self contained with a 2200 mah LiPo in the base that powers the tracker and goggles. The LCD is the user interface for setup and adjustments. There is a single cable coming from the base (not in the photo), that goes to the goggles, or monitor, it supplies 12 volts, audio / video. There is a second plug in to the base that supplies video for a "passenger". The size is approximately 9 inches in diameter with the console on one side. This is the prototype and there is some finish detail to be done.
|Oct 26, 2013, 11:29 AM|
|Oct 28, 2013, 05:23 PM|
|Nov 11, 2013, 02:55 AM|
Thanks for the video. Looking good.
I can't help wondering why no one uses the Baby Orangutan which has numerous analogue to digital converters, 2 motor drivers built in and is about 20 bucks. Using Atmel studio it is a cinch to progam in C and works very well. It doesn't have an LCD display but you can debug with the onboard LED.
I am using one for my RSSI tracker and it is a joy to use and program. I have yet to test it outside with a real aeroplane but I will do soon. I'm not using any fancy filter like Kalman as it is unnecessary with the proper code.
|Nov 12, 2013, 09:08 PM|
The latest code was flown with this weekend and I am quite pleased at the smoothness and precision. I am working on the schematic drawings, PCB traces and pics of the build. I will get it all posted soon.
|Nov 21, 2013, 11:18 AM|
Until this point in the testing the center receiver / antenna has never been used since the focus was to have the tracker move smooth with no jumpiness and that has been best observed watching its movements directly. The code is almost there so the center antenna and goggles were added only to find out there was a bit of "noise" on the video signal. it took a few days to track it down and come up with a solution. The parts should be here today, then I will make new PC boards and should be back on track.
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