Sub-GHz RF Studio Power Automation

Sub-GHz RF Studio Power Automation (`pikvm-studio`)

This page details the wireless sub-GHz RF power control infrastructure in the studio, including the hardware transceiver, mathematical reverse-engineering of the 33-bit Princeton/Fosmon PWM protocol, complete device payload database, and CLI controller.

1. Hardware & Physical Setup

All lighting, outboard gear racks, monitor speakers, and peripherals in the studio are switched via 433.92 MHz RF wireless power relays controlled by a dedicated transceiver plugged into pikvm-studio.

Host Node: pikvm-studio (PiKVM V4 Plus, Raspberry Pi 4 Model B, Arch Linux ARM)
Transceiver: Great Scott Gadgets YARD Stick One
USB ID: 1d50:605b (OpenMoko / GSG RfCat CC1111)
Antenna: Sub-GHz vertical SMA whip antenna
Carrier Frequency: 433.92 MHz
Modulation: ASK / OOK (Amplitude Shift Keying / On-Off Keying)

+--------------------------------------------------------------------------------+
| Host: pikvm-studio (Arch Linux ARM)                                            |
|                                                                                |
|  [ studio-power CLI ] ---> [ RfCat / rflib ] ---> [ YARD Stick One (CC1111) ]  |
+-----------------------------------------------------------------------|--------+
                                                                        | 433.92 MHz ASK/OOK
                                                                        | (33-bit PWM)
                                                                        v
+------------------+  +------------------+  +------------------+  +------------------+
| Moroccan Lamp    |  | Recording Rack   |  | Studio Computer  |  | Subwoofer        |
| (Fosmon Outlet)  |  | (Fosmon Outlet)  |  | (Fosmon Outlet)  |  | (Fosmon Outlet)  |
+------------------+  +------------------+  +------------------+  +------------------+
+------------------+  +------------------+  +------------------+
| Main PA Speakers |  | TV Monitor       |  | Neewer LED Panels|
| (Fosmon Outlet)  |  | (Fosmon Outlet)  |  | (Fosmon Outlet)  |
+------------------+  +------------------+  +------------------+

2. Protocol Specification (Princeton / Fosmon 33-Bit PWM)

The wireless relays in the studio use the 33-bit Princeton / Fosmon Pulse-Width Modulation (PWM) encoding over a 433.92 MHz ASK/OOK carrier.

Timing & Waveform Structure

Fundamental Clock Tick Period ($T_e$): $291.75,\mu\text{s}$ ($\approx 3428\text{ baud}$)
Bit Symbol 0:
- $1 T_e$ High ($292,\mu\text{s}$)
- $3 T_e$ Low ($875,\mu\text{s}$)
- OOK Bitstream Pattern: 1000 (4 ticks / $1.167\text{ ms}$)
Bit Symbol 1:
- $3 T_e$ High ($875,\mu\text{s}$)
- $1 T_e$ Low ($292,\mu\text{s}$)
- OOK Bitstream Pattern: 1110 (4 ticks / $1.167\text{ ms}$)
Sync Pulse:
- $1 T_e$ High ($292,\mu\text{s}$)
- $31 T_e$ Low ($9044,\mu\text{s}$)
- OOK Bitstream Pattern: 1 + 31 zeros (32 ticks / $9.336\text{ ms}$)

Bit '0':  +---+
          |   |___________________   (1 tick high, 3 ticks low)
          <Te><------ 3Te ------->

Bit '1':  +---------------+
          |               |_______   (3 ticks high, 1 tick low)
          <----- 3Te ----><--Te-->

Sync:     +---+
          |   |____________________________________________________  (1 tick high, 31 ticks low)
          <Te><---------------------- 31Te ----------------------->

Complete Frame Composition

Each command transmission consists of: $$\text{Frame} = 33 \text{ data bits} \times 4 \text{ ticks} + 32 \text{ sync ticks} = 164 \text{ ticks} = 47.85\text{ ms}$$

Transmissions are repeated 5 to 10 times consecutively to guarantee reliable reception across physical barriers.

3. Studio Device Payload Database

Every studio outlet has a dedicated 33-bit code for ON and OFF. Below is the complete, mathematically decoded bitstream database:

Device Key	Device Name	Description & Safety Notes	State	33-Bit Binary Bitstream	Hex Payload
`mrc`	Moroccan Lamp	Decorative ambient studio lighting	ON OFF	`110100001100000100001011011110100` `110100001100000100001010011110110`	`0x1a18216f4` `0x1a18214f6`
`rack`	Recording Rack	Preamp rack, compressors, FireWire interfaces	ON OFF	`001011011010100100001011100110000` `001011011010100100001010100110010`	`0x5b521730` `0x5b521532`
`computer`	Studio Computer	DAW PC power outlet (requires PiKVM wake)	ON OFF	`001011011010100100001101100111110` `001011011010100100001100100111100`	`0x5b521b3e` `0x5b52193c`
`sub`	Subwoofer	Studio active subwoofer monitor	ON OFF	`010110100111010000001101000111000` `010110100111010000001100000111010`	`0xb4e81a38` `0xb4e8183a`
`pa`	Main PA Speakers	Main active monitor speakers	ON OFF	`010110100111010000001011000110100` `010110100111010000001010000110110`	`0xb4e81634` `0xb4e81436`
`tv`	TV Monitor	Studio display monitor & Chromecast	ON OFF	`010110100111010000001111000111100` `010110100111010000001110000111110`	`0xb4e81e3c` `0xb4e81c3e`
`neewer`	Neewer LED Lights	Video and photography LED studio lighting	ON OFF	`001010010110011000001111010101110` `001010010110011000001110010101100`	`0x52cc1eae` `0x52cc1cac`

4. Signal Synthesis Implementation (Python)

To generate and transmit any command from scratch using rflib:

#!/usr/bin/env python3
import sys, time
sys.path.insert(0, "/tmp/rfcat")
import rflib

def synthesize_pwm(bit_string):
    """Converts a 33-bit code into a mathematically pure 3428-baud OOK payload."""
    raw_bits = ""
    for bit in bit_string:
        if bit == '1':
            raw_bits += "1110"
        elif bit == '0':
            raw_bits += "1000"
    # Append Sync: 1 tick high, 31 ticks low
    raw_bits += "1" + ("0" * 31)
    
    # Pad to byte boundary
    while len(raw_bits) % 8 != 0:
        raw_bits += "0"
        
    return bytes(int(raw_bits[i:i+8], 2) for i in range(0, len(raw_bits), 8))

def send_signal(bit_string, repeats=10):
    payload = synthesize_pwm(bit_string)
    d = rflib.RfCat()
    d.setFreq(433920000)
    d.setMdmModulation(rflib.MOD_ASK_OOK)
    d.setMdmDRate(3428)
    d.setMdmSyncMode(0)
    d.setMaxPower()
    d.RFxmit(payload * repeats)
    d.cleanup()

# Example: Turn ON Moroccan Lamp
send_signal("110100001100000100001011011110100", repeats=10)

5. CLI Tool: `studio-power`

The utility is permanently installed on pikvm-studio at /usr/local/bin/studio-power.

Command Syntax

# Toggle individual devices:
$ sudo studio-power mrc on
$ sudo studio-power mrc off

$ sudo studio-power rack on
$ sudo studio-power rack off

$ sudo studio-power computer on
$ sudo studio-power computer off

$ sudo studio-power sub on
$ sudo studio-power sub off

$ sudo studio-power pa on
$ sudo studio-power pa off

$ sudo studio-power tv on
$ sudo studio-power tv off

$ sudo studio-power neewer on
$ sudo studio-power neewer off

# Session management (turn entire studio on or off):
$ sudo studio-power all on
$ sudo studio-power all off

# List devices:
$ studio-power list

Sub-GHz RF Studio Power Automation