The Hobbyking E-OSD is a simple yet useful OSD to have. For my mini quad I don’t really need anything fancy like GPS or real time current, all I need is voltage level. However we can also read the RSSI level using the osd since it has two voltage inputs (Bat inputs). In this post I will describe how I hook up the E-OSD RSSI with my Frsky D8RXP receiver.
PWM RSSI Signal
Beware, the RSSI output is not a continuous voltage, but pulsed PWM signal. To use it on the e-OSD, we need a low pass filter, which consists of a resistor and a capacitor, just choose between 10-22k resistor and 1-5uF capacitor should be fine. Connection is shown below.
When hook up everything, battery, video transmitter, camera, and the radio receiver that is able to output RSSI value, you will have these connections.
To make things easier, I made a very simple low pass filter cable with a spare servo lead.
Check RSSI on E-OSD
To check this in the house (i am lazy to go out), I turned on the Range Test on my transmitter module (available on the Frsky DJT). It basically reduce the transmission power to 1/30, so the signal strength is reduced and range can be determine much easier, without flying the model or walking the model to the max range (which could be 1.5KM!)
The range of the RSSI value is between 3.7V to 0.2V (For me), 3.7 being perfect signal. And you should have something like this (sorry I don’t have a DVR to take picture of my monitor, so I found a picture from google image as an example)
To use percentage instead of voltage to represent RSSI, check out how to flash E-OSD with custom firmware.
I followed this instructions on the Frsky Manual, and it works great.
It is highly recommended that you perform a pre-flight range check. Caution must be paid when you do a range check in an environment with metal fences, concrete buildings, or rows of trees. Loss of signal may be experienced around these objects. Follow the steps below to perform range check with a completed model: 6.3.1 Place the model at least two feet (60cm) above the ground (like on a wooden bench). Shallow buried metal may disturb this check. Keep any part of the model’s receive antenna off the ground. 6.3.2 Place the antenna of the transmitter in a vertical position. 6.3.3 Turn on the transmitter and receiver, press the F/S button of the transmitter for 4 seconds to enter the special range check mode, the RED LED of the transmitter module will be off indicating much reduced power output. The effective working distance will be decreased to 1/30. 6.3.4 Walk away from the model while simultaneously operating the controls on the transmitter, confirming that all controls are completely and correctly operational at least 30 meters away. 6.3.5 Push and release the F/S button, the transmitter will exit range check mode.
7 Safe Flying Distance The two-way system has a feature to return the Received Signal Strength Indication (RSSI) of the receiver to the transmitter. The transmitter develops an internal voltage representing the receiver signal strength. Alarms are programmed in the transmitter to warn the pilot when the model is nearing maximum control range. These alarms are given arbitrary color designators in this manual (not on the equipment). The meaning each of these levels and the result is given in the table below.
Color Code Meaning Transmitter Green The signal strength is strong No beeps Yellow The signal strength is adequate Single beeps Orange The model is at far, but safe, range Constant double beeps Red The model is near maximum range Constant triple beeps
Note: It is normal to hear an intermittent, and not frequent, single beep as the model flies through signal fade points. Control will not be affected.
A lot of people claimed they have been using 4S battery on this OSD, so I gave it a try, and SMOKE! The E-OSD is now dead.
Although the LED is led up when I connect 5V to the microchip directly, it won’t power up when battery is connected to BAT2 (the power pin), so I think the voltage converter must have been fried and damaged.
It is rated for 2S to 3S, so it’s not under warranty. If you really need to run 4S on the OSD, get the Super Simple Mini OSD. I heard it’s not as accurate when reading voltage as the e-osd, and it’s not programmable, but at least it’s rated correctly for 4S.