Using the PCM to control a LED

[cantdecide]

We're using a custom LED assembly for illuminating the retro-reflective tape and it needs ~300 milliamps at 12V, meaning we can't use DIO, and because it heats up so quickly, we can't directly hook it up to the VRM(having the LED be on during the whole match would probably destroy the LEDs). I would have traditionally done this with a boring transistor, but it was 4 am(when the best ideas are formed) in the morning, and we had no transistors. That's when it suddenly came to us: we already had a device that had regulated 12V outputs which can be controlled via code: the PCM! We hooked up the LED to one of the solenoid outputs on the PCM, and it worked just fine. We checked the manual to see whether doing that was legal or not, and according to Table 4-4 under R53, CUSTOM CIRCUITS(I assume that our LED assembly is considered a CUSTOM CIRCUIT) can be controlled using the PCM. However, I still have the urge to ask: is this legal? It just feels so odd and honestly, it's something I wouldn't have allowed if I wrote the rules.

Kinda off-topic: third party fans for ESCs aren't allowed but wiring lights to solenoid slots is. Rules are weird.

[Poseidon5817]

Originally Posted by cantdecide

We're using a custom LED assembly for illuminating the retro-reflective tape and it needs ~300 milliamps at 12V, meaning we can't use DIO, and because it heats up so quickly, we can't directly hook it up to the VRM(having the LED be on during the whole match would probably destroy the LEDs). I would have traditionally done this with a boring transistor, but it was 4 am(when the best ideas are formed) in the morning, and we had no transistors. That's when it suddenly came to us: we already had a device that had regulated 12V outputs which can be controlled via code: the PCM! We hooked up the LED to one of the solenoid outputs on the PCM, and it worked just fine. We checked the manual to see whether doing that was legal or not, and according to Table 4-4 under R53, CUSTOM CIRCUITS(I assume that our LED assembly is considered a CUSTOM CIRCUIT) can be controlled using the PCM. However, I still have the urge to ask: is this legal? It just feels so odd and honestly, it's something I wouldn't have allowed if I wrote the rules.

Kinda off-topic: third party fans for ESCs aren't allowed but wiring lights to solenoid slots is. Rules are weird.

We used this last year in week 2 and it wasn't an issue.

[cantdecide]

Originally Posted by Poseidon1671

We used this last year in week 2 and it wasn't an issue.

Alright, it's comforting to see that another team has done this.

[richwong]

You could also use a Spike relay to control your LEDs.

[GeeTwo]

The last row of table 4-4 (R53) explicitly allows 1 custom circuit to be controlled by each PCM channel.

Do keep a good eye on the per-channel and total current drawn by the PCM in any given state.

Another alternative is to use a 12V opto-isolated relay module. These can be controlled from DIO ports or relay ports, and are much smaller and less expensive than a spike for custom circuit loads of up to 10A.

[scca229]

Originally Posted by cantdecide

We're using a custom LED assembly for illuminating the retro-reflective tape and it needs ~300 milliamps at 12V, meaning we can't use DIO, and because it heats up so quickly, we can't directly hook it up to the VRM(having the LED be on during the whole match would probably destroy the LEDs).

Can I ask a simple question? How BRIGHT is this LED assembly that would destroy the LEDs over the period of a match? The retro-reflective tape doesn't require all that much illumination and I'm now worried about a proverbial "light cannon" (as I've heard robot mounted flashlights called recently) shining into the opposing drive teams eyes. Remember that you aren't just on level ground but tilted if you are crossing the defenses at all.

Just curious is all...

[asid61]

A 300ma 12v led could be easily cooled by using a 3w led heatsink like the kinds you can find on ebay or local electronics stores. If the led is on a star, using thermal paste and screws to attach it to the chassis would heatsink it enough alone (the stars are usually isolated).

[cantdecide]

Originally Posted by scca229

Can I ask a simple question? How BRIGHT is this LED assembly that would destroy the LEDs over the period of a match? The retro-reflective tape doesn't require all that much illumination and I'm now worried about a proverbial "light cannon" (as I've heard robot mounted flashlights called recently) shining into the opposing drive teams eyes. Remember that you aren't just on level ground but tilted if you are crossing the defenses at all.

Just curious is all...

It's pretty much as bright as the ring light in FIRST Choice, but with much higher light per surface area(the ring light has 15 LEDs and outputs 304 lumen, meaning ~20 lumen per LED, whereas our assembly has 3 LEDs in total and outputs ~275 lumen(LED guy quote), so about ~90 lumen per LED). I'm trying to keep the light disabled as much as possible because of the nuisance factor. At the moment, it's only turned on when the robot is aiming towards the goal, which shouldn't take longer than 3 seconds(and the aim method has a 10 second timeout).

[BitTwiddler]

We use both an LED ring light from Superbright LEDS for the camera targeting as well as a high-power LED for manual targeting. Both lights are driven off the same Spike relay module which we've used in past years.

Note: our lights are pointed upward and we only turn them on when we need to use them. Otherwise they stay off so as not to unduly distract the opposing castle defenders.

[Coach Seb]

Any info on your setup with the Spike relay would be appreciated... i am trying ot get this going with a 12v to 3.3V converter but the 2 LEDs flashlight i used so far don't seem to hold up.... I have a nice bright light at forst, remove power then re-apply and then i can barely see it....