K4-PB

The smallest pixel controller: 4 eFused pixel ports with per-port current monitoring and a DMX header, on a 71 × 67 mm board that fits a small TA-200 enclosure.

This page describes revision v3.0.1 (printed on the board as K4-PB v3.0.1). The K4-PB works with both the PocketBeagle 2 and the original PocketBeagle 1, and nothing blocks the SD card slot.

How the K4-PB differs from the K8, K16 and K32 boards

• No Ethernet on the board. Plug a USB Ethernet adapter or an FPP-supported USB Wi-Fi adapter into its USB-A port. You need one of them to set it up. A "nano" or "mini" Wi-Fi adapter fits inside a TA-200 enclosure.
• One power terminal, 5 or 12 V. It powers the controller and all four ports, so all of them run at the same voltage. 18 V is the absolute maximum; don't use 24 V supplies.
• No differential ports and no expansion port. It drives only its four local ports.
• DMX is a 3-pin header, not an RJ45 jack.
• No real-time clock. The board gets the time from the network (NTP).
• Not protected against a reversed supply. Check the polarity before you power up.

PocketBeagle 1: never connect its USB port to a computer

With an original PocketBeagle 1 fitted, don't power or set up the K4-PB through the PocketBeagle's own USB port (USB tethering). It can permanently damage the K4-PB. Power it only from its power terminal, and set it up over a USB network adapter. With a PocketBeagle 2, USB tethering is safe.

Specifications

	K4-PB
Local pixel ports	4 (PT1–PT4), 3-pin 3.5 mm pluggable, plugs included
Port protection	eFuse per port, about 5.2 A, latching
Power switching	per port (FPP-controlled)
Current monitoring	every port
Differential ports	none
Total strings	4
Power input	1 terminal, 5 or 12 V DC (18 V maximum), powers the controller and all 4 ports
DMX / serial	1, RS-485 transmit, 3-pin 2.54 mm header (ttyS4)
GPIO header	2×4, unpopulated: 3.3 V, GND and six PocketBeagle pins (P1-2 to P1-12)
Audio	none built in. Use a USB sound card.
Ethernet	none. Use a USB Ethernet or Wi-Fi adapter.
USB-A	1
Display & buttons	128×64 OLED, Test-Down / Enter
Real-time clock	none
Temperature sensor	yes
Size	71.1 × 67.1 mm (2.80 × 2.64 in), 3 mounting holes, 4.0 mm
FPP output	BBB48String
Requires	PocketBeagle 2 (FPP 9.5 or later recommended; any 9.x works) or PocketBeagle 1

Board map

Power terminal

The power terminal is at the bottom left: GND on the left screw, V+ on the right. It powers the PocketBeagle, the USB port and all of the logic, and all four pixel ports. FPP shows its voltage as VIN.

• Every port shares this supply, so all four strings must be the same voltage: 5 V or 12 V pixels.
• 18 V is the maximum. A 24 V supply will damage the board.
• Two blue LEDs on the right-hand edge show that the board has power and that its internal 5 V supply is running.

Check polarity before you power up

The K4-PB is not protected against a reversed supply. The controller's own logic is protected, but a supply wired backwards drives the input surge-protection diode, which is likely to burn out. It usually fails as a short, and the board then won't power up until it is repaired.

Pixel ports

The four pixel ports are in a row across the middle of the board, PT1 on the left to PT4 on the right. Each is G D V (ground, data, +V), as printed beneath it. PT1 is FPP port 1, and so on. See Pixel outputs.

eFuses and current monitoring

Every port has its own eFuse, which trips at about 5.2 A and latches off. FPP reads every port's current and turns each port on and off as needed. When an eFuse trips, FPP marks the port with a red icon on Status/Control → Port Status; click it to turn the port back on once the fault is fixed. See Current monitoring.

DMX

DMX is on the 3-pin, 2.54 mm header on the left edge, marked ttyS4:

Pin	Marking	Signal	DMX XLR pin
top	G	Ground	1
middle	-	Data −	2
bottom	+	Data +	3

Make up a cable from a 3-pin socket to an XLR or RJ45 DMX connector, wired as above. The output is transmit-only and can also drive Renard, LOR or Pixelnet through a suitable adapter. FPP calls the port ttyS4. See DMX / serial.

DMX on a PocketBeagle 2 with an older EEPROM

On a PocketBeagle 2, FPP finds this DMX port through a mapping in the cape EEPROM, added in EEPROM 3.0.1 (February 2025). On a board programmed before then, a DMX output on ttyS4 goes to the wrong serial port and nothing comes out. Fix it by updating the cape EEPROM under Help → About → Cape Info (see Updating), or set the DMX output's port to ttyS5 instead. On a PocketBeagle 1, ttyS4 always works.

GPIO header

The 2×4 header position at the top right is not fitted: solder in a 2×4, 2.54 mm pin header if you want to use it. It brings out 3.3 V, GND and six PocketBeagle pins, numbered on the board: P1-2, P1-4, P1-6, P1-8, P1-10, P1-12. Use them in FPP's GPIO Inputs for buttons or switches to ground. They connect straight to the PocketBeagle, so they are 3.3 V only; never connect 5 V or anything higher.

Other connectors

Connector	Marking	Details
USB-A	—	1 port, top left, for the network adapter. USB
OLED	GND 3.3 SCL SDA	Controls & display
Buttons	Test/Down Enter	Down and Test share one button. Controls & display

FPP setup

When FPP detects the K4-PB it sets itself up automatically. It enables the K4-PB pixel-string layout (FPP's BBB48String output), with each port set to 100 WS2811 pixels at 50 % brightness, the voltage, current and temperature sensors, and a disabled DMX output on ttyS4. Set the pixel counts and start channels from xLights or the FPP Pixel Strings page. See Configuring outputs.

For the first setup, plug in a USB Ethernet adapter and connect it to your network, or use a USB Wi-Fi adapter and FPP's Wi-Fi hotspot. Because the board has no clock, set up NTP under Settings → Time so schedules run at the right time.

Dimensions & mounting

• 71.12 × 67.06 mm (2.80 × 2.64 in), 3 mounting holes, 4.0 mm, for M3 or M3.5 (or #6) screws.
• Designed to fit a TA-200 enclosure.
• Use standoffs at least 6 mm (¼ in) tall, so nothing on the underside touches the enclosure.