Whilst I’m not into FPV, I use an Eachine LCD5800D monitor to check the view from the Raspberry Pi companion computer of The Groundhog. With the super-imposed graphics, it gives a constant view of the status of the image lock on target etc. It also has a nifty built-in recorder.
Recently the link refused to work, and after first replacing the transmitter, I realised it was actually the receiver that had failed. I decided to upgrade the receiver, hopefully fitting a new unit within the existing case.
A good briefing on the internals is to be had from the excellent YouTube video from Albert Kim at https://www.youtube.com/watch?v=P7A6fKBtbXM.
The Eachine RC840 seemed a good candidate for the replacement. Diversity was not needed and the RC840 has an audio capability not present in the original, even thought the built-in recorder can accommodate an audio signal if provided. This might prove a useful addition for the future. Furthermore, the RC840 is more sensitive and so can support a greater range if needed.
The supply voltage for the RC840 is specified at 12V. However, I had it on good authority that it can be driven by the 7.4V battery in the monitor unit and a quick test seemed to confirm this. It doesn’t have auto-tuning, but it was considered this was not an issue either, as normally the Groundhog is flown alone in a field, so there is no need to keep changing channels.
It quickly became apparent that the RC840 would not fit inside the existing monitor casing, even with the (good quality) metal casing removed. So a decision was made to mount it externally.
The existing receiver (below) was disconnected and removed after the battery was taken out to guard against short-circuits. The three wires connecting the receiver were extracted from the connector block – video, supply and ground.
The video and ground wire was connected to an RCA phono socket for an external connection. Conveniently, the phono socket fitted the old antenna hole perfectly. The supply and further ground were run out of the casing to be terminated externally ready for connection to the RC840 power lead. As shown below, some hot glue and heat-shrink were used to give strain-relief for the supply wires.
The new connections are shown below. Note the recorder lower left. It has an audio connection which could be wired up in future, if desired. The usb charging circuit is lower right.
The final results are shown below. The supply and video signal wires to the RC840 receiver are coiled reasonably neatly on the back of the monitor. Given that the monitor will now be used on tripod, it would also be possible to mount the receiver separately, perhaps higher up to improve range.
I’ll be using the new monitor set-up in the next few days to record The Groundhog doing some more line following – given a break in the weather!