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DragonOSD+ calibration procedures

Posted: Fri 16 Apr 16 2010 9:59 am
by Daniel Wee
RSSI Calibration

For those wishing to calibrate their RSSI, the procedure is as follows:-

1. Make sure that RSSI is connected and you have some functionality
2. Turn the transmitter off
3. Adjust the RSSILOW parameter until the RSSI reading just reaches 0%
4. Turn the transmitter on (near the receiver)
5. Adjust the RSSIHIGH parameter until the RSSI reading just reaches 100%
6. Save the settings to EEPROM when you are satisfied with the results

Some notes about this:-

1. There will be some fluctuation of the RSSI reading so it's not unusual to see the readings jump between 0% to 7% on the low side for example. The high side values tend to be more stable but then again, do not be surprised at some fluctuation.

2. The RSSI reading is actually a voltage reading so that you can actually measure the RSSI line with a DMM to get an idea of what the voltages are. This way you can enter the voltages directly rather than take a trial and error approach to find the threshold readings. Having said that, it is probably still necessary to tweak it a bit to get the readings exactly right because the calibration of the board voltage readings may not be as accurate as that of your meter (or vice versa).

3. When using the menu to make this adjustment, it is necessary to exit the menu to look at the resultant readings. When using the serial terminal to make this adjustment, you should be able to see the change immediately. The serial commands take the form of:-


4. All of the above assumes that you have already activated the RSSI percentage display. This would be the G.P. Input mode 2, which can also be set using the serial terminal command:-


Some of you may notice that there is a GPMODE 3. I do not recommend using this (dBm display) because you will need to calibrate this very accurately for it to make any real sense at all.

5. It should be fairly common knowledge at this point that some receivers will require a buffer for the RSSI line. The reason for this is three fold:-

a) the RSSI voltage is used for internal AGC (gain control) purposes of the receiver
b) it was not really meant to drive an external ADC (such as found on the OSD)
c) because of a & b, the RSSI voltage may be pulled too low and cause the receiver to malfunction

Some receivers such the the DragonLink do not have this problem but many of the other receivers do. If you need such a buffer, you can try the following link:- ... ge=14&js=n

6. Different receivers will require different calibrations, even if they're the same model and make.

7. For those of you who are planning to fly long range, I would suggest not going below about 30% to be on the safe side, unless you are equipped with a functioning RTH system.


Re: DragonOSD+ calibration procedures

Posted: Wed 26 May 26 2010 12:32 pm
by Daniel Wee
Current and mAh Calibration

To start with, if you are using the SFE Atto-sensor, your Current Offset value needs to be at 0.0. Also make sure that the resistor indicated in the link below, has been removed:-


If you are using an Allegro based sensor, you may need to set the Current Offset to whatever the output voltage of the sensor is when there is no current flowing through it.

The current reading should be calibrated before use. Ideally, you'd connect a Wattmeter in series and power up the motor and watch the current reading on the Wattmeter and compare that to the OSD reading. Then you would adjust the Current multiplier (IMULT) such that the two match up.

Suppose that the wattmeter reading is IW and the OSD reading is IO, and the current multiplier is M1 during the test. The adjusted value for the multiplier should be M2 where:-

M2 = IW / IO * M1

You should also calibrate the mAh reading. This is done by flying a fully charged pack and noting the final mAh reading. Then charge the battery with a charge that reports the amount of mAh going into the battery. Note the differences and then adjust the mAh multiplier such that they agree.

Suppose that the mAh reading on the charger for a full top-up charge is WT and the mAh reading indicated at the end of the flight on the OSD is WO, and the mAh multiplier is presently M1, then adjusted multiplier should be M2 where:-

M2 = WT / WO * M1


Re: DragonOSD+ calibration procedures

Posted: Wed 26 May 26 2010 12:45 pm
by Daniel Wee
V1 and V2 Calibration

Because of component variations about the tolerance values, the voltage readings may not be as accurate as it could be. If you want the highest accuracy for the voltages read, you should calibrate them. In order to do so, you will need an accurate digital multi-meter (DMM).

Let us start with V1, which is the supply voltage for the DOSD+ board. Whatever voltage present on these pins will be read as V1. Note that if you are powering the board using the current sensor board and jumpering J1, then V1 and V2 are connected and the same voltage is being read by both channels. Nevertheless, both channels need to be calibrated individually.

Hook up the power to the DOSD+ and see what the reading at the top left corner is (assuming that you have not disabled the display). Let us call this reading VOSD. While still connected, use the DMM in DC-voltage mode and measure the voltage across the battery terminals. Call this reading VDMM. Assuming that the V1 multiplier is presently M1. The new adjusted value for the V1 multiplier should be:-

M2 = (VDMM / VOSD) * M1

The multiplier for V2 is determined in the same way. Connect the current sensor to the DOSD+ board and then connect a battery to it. Note the voltage reading at the bottom left group and call that VOSD. Measure the voltage across the battery (which is connected to the current sensor) terminals using the DMM in DC-voltage mode, and call that VDMM. Where the present V2 multiplier is M1, the new adjusted V2 multiplier is given as M2 using the above formula.

Be sure to save your changes.