Is there a 3.3V source I can use in SLB? I only see 5V and 24V options. The reason I need it is that I have an external microcontroller that only accepts 3.3V as digital HIGH, and I want to connect this as a source for SW1 or SW2. I’m trying to avoid adding a voltage divider to my wiring if possible.
Additionally, is there any documentation for the GPIO 40 pins? Is this compatible with the Raspberry Pi? My main concern is whether it can power the Pi through the 40-pin header.
@siganberg, we didn’t end up needing any 3.3V or 12V power on the board so we only have 24V and 5V unfortunately. Regarding the 40-pin output, we chose that size since the connectors used for Pis are very prevalent, which would make setup more accessible, but the hookup is not Pi compatible. It’s more a combination of assorted pin outputs - some are duplicates from other spots on the board and some are novel. I haven’t had the time to document it in a readable form, but the pinout for the design can be referenced in our open source files if you’re savvy: (see page 19) SuperLongBoard/Project Outputs for Longboard_32bit/Schematic and 3D Prints/Longboard_32bit_Schematic_B6.1_FULL_PLACE.PDF at master · Sienci-Labs/SuperLongBoard · GitHub
Thanks, @chrismakesstuff! I was able to get 3.3V scavenging resistors from a bi-directional level shifter by creating a voltage divider.
FYI, the bi-directional level shifter doesn’t work in my case because my microcontroller’s I/O pin has a pull-up resistor. I think the SLB FLOOD I/O 5V is floating when it’s off (neither HIGH nor LOW), so I have no way to know if it’s off from my microcontroller. What worked was converting it to a voltage divider, which also acts as a pull-down resistor for my I/O pin.
Just FYI - voltage regulators are dirt cheap at Aliexpress. You are looking at probably less than $3 for a tiny board that takes in let’s say 5V and spits out 3.3V. Adjustable regulators are slightly more money but still dirt cheap.
While voltage dividers are a quick fix, they depend on load current. Ok if your load current is fixed but with a voltage regulator being as cheap as they are, why not use them. I would never use a voltage divider for powering a microcontroller since load current varies and microcontrollers tend to be voltage sensitive. A Raspberry pi for example has a lot of issues with aftermarket power supplies being ever so slightly low in output voltage.
Since lead time from Aliexpress is somewhere around 3-4 weeks for me, I carry stock on cheap stuff like that.
This isn’t about powering the microcontroller—it’s about level shifting the I/O output signals from 5V, which the SLB is sending, down to 3.3V for the microcontroller’s I/O pins. Feeding 5V directly to an I/O pin will damage the microcontroller. Voltage level shifters were designed for this purpose, but most are intended for bi-directional signals, commonly used in serial digital communication like SPI. On the SLB side, the signal is floating when is OFF, while on the microcontroller side, it’s set as INPUT_PULLUP, meaning there’s no way to detect LOW on my I/O pins. A voltage divider is actually perfect for this scenario cause it also act as PULL-DOWN.
By the way, I also tried using a simple voltage regulator at first, thinking it would work, but it wasn’t fast enough for switching between HIGH and LOW signals, which is critical for my application.