Hi there, I come asking for help, perhaps because I'm being a nOOb, and perhaps because my question is a really hard search term.
I'd like to connect an arduino to an existing RX PCB inside an RC toy, and be able to sense when an SD card is written to. This will allow me to repurpose the RECORD button on the TX (which controls a feature I won't use) to do something else - see below:
I have a project where I'm modding a Nerf toy called a Terrascout (worth a google if you're interested). It's like a toy RC tank that fires nerf darts and has first person video with a screen on the transmitter.
The mod pathway for upgrading the Terrascout's flywheel powered blaster is well-trodden, it's all about intercepting the stock motor signals (via opto-isolation) and triggering a MOSFET to control beefier motors connected to a beefier battery - easy peasy stuff.
Where it gets interesting is that I figure I can put an arduino into the (well trodden) mix for finer a few features of my own. Perhaps voltage to the motors being tunable by PWM; controlling the dart pusher motor to fire 1, 3 or 5 round bursts each time the trigger (on the TX) is pulled, or tapped, or double tapped etc; or adding switches to sense various things.
What has me really excited, is that the Terrascout has one feature I won't use, but is controllable from the TX. It has a record button which starts recording from the onboard 480p camera (which streams live to a screen on the TX). The recording goes onto an onboard SD card.
I won't be using the above 480p recording feature because it's 2021 and I can strap a gopro to the thing. Buuuut, that leaves me with the tantilisign prospect of repurposing the REC button on the TX to do whatever I like.
I've read-up a little on the SD / SPI interface, and don't properly understand it. Apart from intercepting start bits, is there a simpler way to let an arduino know when the REC button on the TX is on or off (it latches)? I haven't yet seen the RX PCB in real life, but don't think there is anything easy like a red LED that lights up for recording.
Any ideas would be appreciated.