a. Current sensors

Current sensor, in my opinion can only be used in a warm countries.

In places where winter and summer have large temperature differences, there are also large differences in temperature as function of height.

At the airport can be 22 degrees Celsius (warm) and only 7 degrees (cool) at a 150m height or less at a higher altitude.

Unfortunately, Li-Pol effective capacity depends a lot on the temperature, at low temperature just quickly fall.

So, Capacity consumption (mAh) calculated by current (current sensor) and a time, is displayed as expected of nominal battery capacity. But in fact, it is different from the actual power remaining in the battery. So, the capacity measurement based on the current sensor, simply lie about the real state of the battery when temperatures are low.

In my opinion, the voltage is the only factor, we can estimate the true state/condition of Battery at the moment, in most accurate way. Voltage never lay about the actual battery condition.

Anyway, the OSD allows you to connect the current sensor and shows the capacity (mAh) drawn from battery (remember, capacity of the Li-Pol, depends on temperature).

Well, if someone wants to build and use a current sensor - this is not a problem.

This PCB can also be used as a Power Board, to spread the power of T or XT60 connector to other parts, such as camera, VideoTX and OSD.

The current sensor connection - in fact, is easy part.

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Universal PCB, allows you to use chip INA138, INA139, INA168, INA169 to build current sensor.

The image below, shows a board and place when to soldering INA series chip, R = 100kOhm, C = 100nF

This picture below, shows ready to use current sensor, done with IC INAxxx

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PCB INA138, INA139, INA168 or INA169 chip is basically the same chip used in Pitlab's or Flytron's current sensor.

I-sense resistor (shunt) should be one 0.002 Ohm, or two parallel resistors (summary 0.001 Ohm) for the current over 35Amps.

Because the OSD has ability to calibrate the current sensor, calibration works very well, as the current sense resistance (shunt) can also be used a piece of copper wire (not too thick), this for example can be 50Amps car fuse (use the appropriate current for the installation), which also protects against Shortcut and possible fire.

For example, the sensor below works with 0.04055 gain value, so as shunt can be used more thicker wire, which increases the maximum current value

Anyway - now all OSD kits include bare PCB current sensor.

I think that most users will build a current sensor based on this board easy - especially, as the INA139/168/169/138 are available for free, as samples from the Texas Instruments web site, they ship 4-6 chips without problems.

This sensor is powered from the battery - so you do not need to made any Vcc to run. For proper current measure, sensor needs to connect only black (GND) and purple (signal for ADC).

Note, that the red (Vcc) cable, is not sensor supply - it is for measurement of the Battery voltage, connected to the OSD ENGine input.

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OSD works with any type of sensor, providing analog output signal, proportional to the current flown by current sensor.

FIRST of all, we must know, if our sensor module needs 5V supply for proper operation or don't need any Vcc supply, as it is already powered by measured battery.

For example, very popular sensors Allegro

It needs 5V supply, taken from the OSD or whatever other source.

There are a few tips, sensors can have already soldered 5V power source (ex. small stabilizer LDO), near Allegro current sensor on the same board.

If sensor needs 5V, than we have to prepare 5V from OSD, alco GND and the signal from the sensor to the input ADC6 - so 3 wires must be prepared signal, 5V, GND.

Described here is another $1 DIY project of user "mmormota", sensor is described here http://www.rcgroups.com/forums/showpost.php?p=12479839&postcount=814

This sensor does not require a 5V power supply, because is powered by the measured battery.

In fact, most of the sensors can be made as DIY using any op-amp, rail-to-rail type.

- Diagram of Flytron is on his website, the same solution Pitlab.

So, when sensor do not need external Vcc , we need to prepare only two wires, signal (to ADC6) and GND.

Some users have tested the OSD with Flytron's current sensor with success:

https://sites.google.com/site/remzibiosd/5-external-sensors/5-current-sensors/50a-current-sensor-for-simpleosd.jpg

https://sites.google.com/site/remzibiosd/5-external-sensors/5-current-sensors/ultralight-50ah-current-sensor.jpg

Other sensors, such as Pitlab, good quality and not expensive, also works well with the OSD

Here is a sample, how to connect a Pitlab sensor with remzibiOSD:

Connection is for measurement of current and voltage of the battery.

If the main battery is not connected to the Video battery's GND, then connect as shown below.

Or you can simply connect main battery GND to any OSD GND pin (ex. GND of Video)

If both battery have common GND, so the only one positive wire from ENGine battery, to the positive pin of ENG input, must be connected (to ADC6).

If only one battery is used to power all electronic gear (Engines and Video), then ENG input is not used.

In the same way, we can connect Flytron's sensor to the remzibi OSD.

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More about GND - this is important

About GND - if we use ENGine Voltage measurement input with GND pin used (or if GNDs of both battery is externally connected as one common GND) - so we do not need to double GND connection to the current sensor - In this case, only one signal cable need to be connected to the current input (ADC6) .

In any type of Current Sensor connection, calibration in each case is the same - when is current 0 Amps, then zero value is read at ADC6 (except, when at zero current sensor give small ADC value - so use it as a Minimum Value).

Then, turn on well-known current, ex. 10A current (measured in parallel by the multimeter) - and read the ADC value at ADC6 (press pooling button in GUI in ADC window) when current 10A flow - we can scale the ADC6 value to the "proper value" to show on the screen the proper 10A current - type in Desired Output 10 - gain will be counted automatically - that's all, press "Programm OSD" button to save those gain value in OSD.

As additional information - current sensor can be connected to any ADC input and calibrated - but only, when connected to the input ADC6, OSD will calculate and show the energy consumption information in virtual ADC7.

So, is possible to connect more than one current sensor to OSD, but consumed capacity of the battery mAh (at ADC7), will show only when current sensor is connected to ADC6 input (I2 pin) .

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