c. Frequency meter ex. Hall sensor

Frequency meter with gain (scaling ability) is located at T0 input , input have pull-up resistor enabled inside chip .

T0 input is located at new boards design v1.1 and v1.2 (or RCL input old board-must be soldered SMD resistor about 220ohm-512ohm) .

Frequency meter can be used with magnetic Hall's effect sensor or optical sensor with any mechanical sets . Can be scaled as Hz or RPM (gain=60) or whatever need .

The main idea , is to deliver to T0 input square signal , each falling edge will trigger frequency meter's interrupt , then each second OSD will display counted waves - it means show you frequency in Hz .

If we want the value to be scaled and displayed as RPM (Round Per Minute) then we must made gain=gain * 60 (multiplication by 60), because 60 second is in one minute.

If you have more magnets on axis , on one turn ex. 4 - for scale as Hz made gain=gain * 1/4 =gain * 0,25 (multiplication by 0.25).

T0 also can be used as RX frames counter when connected to any empty RX output (50Hz output from T9X TX for example) - scaled as percentage then gain=2 , because 50 * 2 =100% , when less the less percentage will be displayed .

But much better is to connect T0 to any flashing LED in 2,4GHz receiver to see the receiver range condition or LED flash indication , flashing frequency will be showed .

As main sensors can be used optical sensor - like photo diode from printer (detect if paper are at place).

Or Hall effect sensor - works giving changed waves of voltage depend from changed magnetic field around .

Those Hall sensors are easy to find out at old HDD, FDD, CD (near motor) or whatever PC fun with RPM measure ability (yellow wire is hall signal output from fun) .

Typical Hall sensor have open collector output - so it is OK because the T0 input have internal pull-up to Vcc .

Typical Hall sensor looks like that

http://www.rcgroups.com/forums/showpost.php?p=12474438&postcount=790

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And example how to made an excellent Hall sensor from old PC fan .

IMPORTANT - check your fun chip datasheet as some of them have another outputs and works in different ways .

First must make fun as pieces , all coils should be out .

There is already diode on Vcc so any opposite connection is not danger to fun's electronic.

Then instead of one coil - we put one resistor 50-75ohm - that works the best way (do not look at picture is 150 but is too much - can be two of them parallel) .

On OSD (new board type) I used GND near Video input , 5V - red cable , signal -white cable connected to pad named "T0"

(in old board it is RCl input with resistor SMD about 220ohm but can be just shortcut) .

Such Hall sensor works with any moving magnet , ex. glued to any motor axis , work as RPM or Hz measurement depend of input configuration (scaling using gain).

Or using with any fun rotor to measure for example air speed after scaling (using gain) .