HUD, Head Up Display

on screen info on the analog FPV goggles output for the Hubsan H501S quadcopter

This project is released under the GPL license



I designed and build an on screen character generator that displays on the analog goggles output the info you normally only see on the remote LCD


Screen view, all messages are relayed, except tilt and roll, mainly due to limited screen space, and not sure that info helps a lot:
hud_view_IMG_5976.JPG

Circuit diagram, I added a 22uF/25 V electrolytic capacitor from the regulator output to ground to reduce LF noise on the supply.
Please note that the circuit is designed for 4 normal AA batteries, if you want to put in 7.4 V or more, then you need a bigger transistor for the BC547 and a heatsink, or better use a switcher,
Note that there exists several package versions of the SAA5281 chip, some have smaller pinout and more pins, and DIFFERENT pin numbering, so check the datasheet,
this is the SOT240-1 DIP 48 version:
hubsan_h501s_hud_circuit_diagram_IMG_6746.JPG


Build it, component view.
There is also a hole under the PCB where the power and AFC_RX wires enter the remote.
The little empty sockets are for testing (serial port) and programming the PIC:
H501_HUD_PCB_in_box_IMG_5993.JPG


Wiring side, note the small SMD components:
H501S_HUD_PCB_wiring_side_IMG_5994.JPG


I mounted it on the left side of the remote control, the switch powers it, or switches it off, when switched off it shows the normal analog output without info:
H501S_HUD_box_on_side_remote_IMG_6005.JPG


This shows the connection made to the remote controller, note I use ground from the battery - point (brown wire), and take the + after the on/off switch (yellow wire).
The remote AFC_RX testpoint feeds into the box via a series resistor, to protect the remote against shorts (grey wire).
There are some more wires, and the little board at the bottom is the auto pilot, it is still being modified as I want to add a drop command,
for that I use the LED switch, and the transistor next to the AFC_RX point connects with wires to the other side of the board to the LED switch,
more about that later when I got all parts in:
H501S_HUD_box_connections_to_remote_IMG_6001.JPG


Current consumption is about 75 mA, powered from the remote controller batteries.
It would be easy to make a PCB for this.



The asm code for Microchip PIC18F14K22, this is NOT for MPlab, I use gpasm in Linux:
hud_to_waypoints-0.1.asm
And for those who cannot assemble it, here the hex file:
hud_to_waypoints-0.1.hex
These are new versions of the software that accomodate logging the flight to a PC via USB, or using the log_pic flight recorder.
The optional USB module is a standard ebay USB to logic level board, and located in the cable, not needed if you use the fight recorder.
One record per sector of 512 bytes is written to the sdcard every 2 seconds,
the format is:
11 N53.2512398 E005.5995891 S0.7% A1.5m 0 H143 54
where 11 is the number of satellites the drone uses, then latitude, longitude, airspeed, altitude, commands, heading, waypoint_name
waypoint name is an increasing number.
commands is not used in this version.

Note on the asm,
there are a number of defines at the start of the source file, With only the number of satellites for remote and drone displayed more screen area is visible for flying.
And you only need that info to make sure you have enough sats for GPS, the exact location is usually known.


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