My guess is that it's a simple relay that flips closed for a period of time when the first car passes the finish line, but I could be wrong and it's something else like a high/low voltage change?
I'm building an interface circuit so that I can use that 'photo finish' output to send a hotkey keystroke to OBS to trigger a slow-motion replay, vs doing it manually after every race...
My plan is when that 'photo finish' is triggered, wait for say 2 seconds (so the other cars finish) then send the hotkey keystroke to OBS that will then play the previous 7 or 8 seconds of race video in slow motion and then return to the live main video feed.
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You can contact eTekGadget to get more info, as they are the ones that provide the electronics for the double sided Champ timer models.
Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
Doh... I don't know how I missed that on their timer tutorial as those settings are in the screenshot of the setup software...
I will do that...
It's as I suspected the tip & ring of the phono jack simulate a normally open momentary switch that closes based on the values in the timer firmware, almost certainly a MOSFET/transistor of some kind, but I'm not going to break the security tape to confirm
Simple enough to interface, I used a Digispark development board between the timer and computer with some simple code... The Digispark detects the champ timer photo trigger, it waits an adjustable amount of time, then sends a keystroke to the computer that triggers the slow motion instant replay in OBS. I was just going to use a hacked keyboard circuit board, but after getting my hands on the timer, I see the max delay is only 255ms and I needed far more delay adjustment than than before the scene change is launched...
I'll fine-tune it on race day, but right now after the first car crosses the finish line and the timer triggers the Digispark, the Digispark waits about 3 seconds (for the other cars to fully finish) then sends a keystroke to OBS, at that time OBS changes to a replay graphic overlay scene, and plays back the previous 10ish seconds of cached video at 50% speed showing the entire previous heat in slow motion, then returns to the live feed with no user interaction...