u/xNyke

I’m not that deep into ELRS yet, so I’m not entirely sure how I should approach this.

Basically, I have an RC car and I’d like to use some of the buttons/switches on my RadioMaster Boxer ELRS to control the LEDs on the car.

The LEDs are wired using a 3-wire cable, similar to a servo. The anode is permanently connected to the positive supply voltage, and I have a MOSFET that connects the cathode to GND when it receives a signal on the signal wire.

From what I understand, the usual receiver output modes are PWM with frequencies such as 50, 60, 100, 160, 333, or 400 Hz, with pulse widths like:

• Normal: 988–2012 µs (center 1500 µs)
• Extended: 885–2115 µs (center 1500 µs)
• Half pulse: 494–1006 µs (center 750 µs)

None of these seem particularly useful for my application, since the LEDs would never really be fully off.

However, I also saw in the documentation that ELRS receivers should support 10 kHz PWM with 0–100% duty cycle or even binary ON/OFF (HIGH/LOW) output. That would be exactly what I need.

The problem is that when I look at different ELRS receivers, I can’t seem to find much information about whether their outputs actually support these modes. As far as I understand, this is something that should be configured in the receiver settings, but I’m not sure how it works in practice.

So my questions are:

1. Can I configure any ELRS receiver output to act as a simple digital ON/OFF output?
2. Do I need a specific receiver that supports this, or can most ELRS receivers do it?
3. How would I configure one of the buttons/switches on my Boxer to control that output in this way?
4. I’d also like to implement turn signals. Can this kind of blinking pattern be configured in ELRS/receiver software, or would I need additional hardware (e.g. a small microcontroller, 555) to handle the blinking?

I’m mainly looking for the simplest/cleanest way to do this without adding unnecessary hardware.

Does this look like correct placement for fiducials and tooling holes?

I have never used them before. Despite trying to follow the standard guidelines, I couldn't find much information on this. Not even on the manufacturer's website. What I found:

Fiducials:

• Clear space around each fiducial: about 5 mm
• Placed near the corners
• Spaced as far apart as possible

Tooling holes:

• Board edge to hole center: minimum 3 mm
• Hole edge to board edge: minimum 1 mm
• Hole edge to copper / traces / zones: minimum 1 mm
• Hole edge to other holes: minimum 1.5 mm
• Hole edge to components: minimum 2 mm

Does this look like a good placement strategy? Also am I missing anything important, or are any of the dimensions off?

I’m designing a keyboard PCB and trying to figure out the best approach for the 5V WS2812 LED rail.

The MCU runs at 3.3V from a TLV76733 LDO, which already handles soft-start. The WS2812 LEDs are powered directly from VBUS. Users may optionally add more LEDs, so the capacitance and inrush current on the 5V rail can vary quite. I already have standard USB input protection in place (ESD + eFuse/current limiting).

What I want for the 5V LED rail is reverse polarity protection plus soft-start, ideally with minimal voltage drop and no need for MCU control.

My current idea is using a load switch like TPS22965 or TPS22910A, tied permanently enabled, since they include soft-start and seem simple to implement. I’m not sure if this is the best approach though.

Are load switches appropriate here, or would a different solution be more suitable?

I want to make sure the design is up to spec. This is the LDO circuit for a keyboard PCB. I plan to use the unified daughterboard, which has most ESD, resettable fuse and CC pull-ups already on it. The D+ pull-up is internal in the RP2350. For ESD safety when connecting, there is a second line of protection on this PCB. I am limiting the use of capacitors before the LDO to a maximum of 10 µF, and the LDO features a soft start for everything after that. Since the board is intended for DIY, I am adding a reverse current protection diode in case someone adds something with capacitance. Have I forgotten anything, and is the MBR130 a good choice here? I want the user to be able to add to the SK6812 leds if he wants. How can I ensure that the capacitance of any additional LED strips is still below 10 µF when there is already almost nothing left?

I have five identical SPI ADCs that sample on CS edge and then return a databit on each clock tick, so there is no MOSI. Only CLK, MISO and CS.
Are there any disadvantages to multiple MISO lines instead of multiple CS lines?
I can only see big advantages, since I can read the entire port at once anyway:

• I can use point-to-point termination very easily without worrying about parallel termination current.
• I can eliminate dead time when changing between the ADC slaves, since I only wait for sampling once.
• I can also use a clock frequency that is one-fifth of the original, or be five times faster.
• The only disadvantage is the risk of crosstalk and rearranging the data in the MCU, but this seems like a minor problem compared to all the benefits.

Am I missing something?