CAST-1 Audio Casting: ESPHome Network Audio Player

You probably already own speakers you like. CAST-1 gives them streaming, multi-room sync, and Home Assistant announcements for the cost of a small board and two cables, without replacing anything.

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CAST-1 Audio Casting: ESPHome Network Audio Player

Meet CAST-1: Your Speakers Are Already Good Enough

 Look at the speakers in your house. The bookshelf pair you saved up for. The old receiver that still sounds better than anything you could buy new for the same money. The desktop monitors you use every day.

There is nothing wrong with any of them. They sound good. The only thing they cannot do is join your smart home.

The usual fix is to replace them with smart speakers, which means spending real money to end up with worse sound and a cloud account you did not want. CAST-1 takes the other path. It gives the speakers you already own streaming, multi-room sync, and Home Assistant announcements, and it leaves everything else alone.

What CAST-1 is, and what it needs

CAST-1 is a small network audio player. It plugs into powered speakers, a hi-fi amplifier, an AV receiver, or a pair of desktop monitors, and turns them into a player your smart home can reach.

Two cables: USB-C for power, 3.5mm aux for audio. That is the whole install.

Being direct about what this is, because we would rather set expectations properly than surprise anyone:

  • CAST-1 is not a speaker. It has no amplifier and no drivers. It needs an existing speaker or amplifier to plug into.
  • The box contains CAST-1 only. The USB-C cable, the 3.5mm cable, a USB-C power adapter, and the W5500 Ethernet HAT for CAST-1 are all sold separately.

If you have a speaker you like and two cables, you are set. If you were hoping for something that makes noise on its own, this is not that product.

At 45 x 45 x 15 mm it disappears behind whatever it is driving.

A DAC worth caring about

Audio runs through a Texas Instruments PCM5122, a 32-bit stereo DAC with 112 dB SNR and dynamic range, -93 dB THD+N, and a 2.1 VRMS full scale line-level output.

That matters because a network streamer is only as good as the converter inside it, and the converter is usually where cost gets cut. If you have spent money on speakers, sending them a clean line-level signal is the difference between hearing what they can do and wondering why streaming sounds flat.

The PCM5122 is a part you would expect in dedicated audio gear, not in a board this size.

Sendspin and multi-room, honestly

CAST-1 supports Sendspin, the open audio streaming and synchronization protocol developed by the Open Home Foundation and built natively into Music Assistant.

Sendspin gives sample-accurate synchronization between players. In practice that means several CAST-1 units stay locked together room to room, so walking from the kitchen to the living room does not produce that hollow echo you get when two players drift apart. We have run multiple units in sync during testing and it holds up well.

Now the honest part: Sendspin is currently a technical preview. It works today, and it is improving quickly, but it is still evolving. We are not going to present multi-room sync as a finished, guaranteed-stable feature, because it is not one yet. If you want rock-solid multi-room today with no rough edges, wait a little. If you are comfortable being early on something genuinely promising, come along.

CAST-1 appears automatically in Music Assistant and Home Assistant through mDNS discovery, so there is no manual IP entry.

Announcements on the speakers already in the room

Outside of music, CAST-1 works as a standard ESPHome media player in Home Assistant. That opens up the everyday things people actually build:

  • Text-to-speech announcements in the room where they are relevant
  • A doorbell chime through the stereo instead of a phone buzz nobody hears
  • Automation alerts: laundry finished, garage left open, a sensor threshold crossed

These are the automations most people set up in their first week with Home Assistant, and they work better through speakers that are already positioned where you spend time.

CAST-1 is also Bluetooth proxy capable, so it can extend Home Assistant's Bluetooth coverage into the room it is already sitting in.

The solder pads, and lights that move with the music

This is the part we find most interesting.

CAST-1 exposes solder pads for 5 V, ground, and IO1. You can drive an addressable LED strip or an external sensor directly from the device.

Here is why that is different from bolting on a second gadget: the audio and the GPIO live on the same board, running the same ESPHome configuration. Lighting can react to playback without a second controller, without a bridge, and without two devices trying to stay in step with each other. Behind a TV, along a shelf, or under a desk, the lights and the audio come from one place.

The firmware is open source and the YAML is yours to modify, which is the real point of building on ESPHome. Build, learn, automate.

Wi-Fi, or wired when it matters

CAST-1 connects over 2.4 GHz Wi-Fi out of the box, which is fine for most rooms.

For everywhere else, there is the optional W5500 Ethernet HAT for CAST-1, sold separately. Wired is worth it when convenience is not the constraint: long runs to an outbuilding, thick masonry walls, a congested 2.4 GHz band in an apartment building, or a rack in the basement where you would rather not think about Wi-Fi again. Synchronized multi-room audio in particular benefits from a network path that does not fluctuate.

Specifications

Hardware

  • Microcontroller: Espressif ESP32-S3, 16 MB flash, 8 MB PSRAM
  • DAC: Texas Instruments PCM5122, 32-bit stereo, 112 dB SNR and dynamic range, -93 dB THD+N
  • Audio output: 3.5mm analog line out, 2.1 VRMS full scale
  • Indicators: RGB status LED
  • Dimensions: 45 x 45 x 15 mm (1.8 x 1.8 x 0.6 in)

Connectivity

  • Wi-Fi: 2.4 GHz
  • Ethernet: via the optional W5500 Ethernet HAT for CAST-1, sold separately
  • Bluetooth: BLE, Home Assistant Bluetooth Proxy capable
  • Discovery: automatic via mDNS in Music Assistant and Home Assistant

Software

  • Firmware: ESPHome, open source, locally controlled
  • Streaming: Sendspin, native in Music Assistant
  • Home Assistant: standard ESPHome media player
  • Cloud required: none, 100% local, no account, no subscription

Power and connections

  • Power: USB-C, 5 V 1 A
  • Ports: USB-C for power and programming, 3.5mm audio out
  • Expansion: solder pads for 5 V, GND, and IO1

In the box

  • CAST-1 only. The USB-C cable, 3.5mm cable, USB-C power adapter, and the W5500 Ethernet HAT for CAST-1 are sold separately.

Frequently asked questions

Does CAST-1 work without Home Assistant? Yes. It works as a Sendspin player in Music Assistant, which runs independently of Home Assistant. The Music Assistant server can be installed with Docker on a Raspberry Pi, a NAS, or a spare PC, and you control it from any browser. Home Assistant is one install option among several, and adding it brings the automation side: text-to-speech announcements, doorbell chimes, and alerts.

Do I need Music Assistant? No, though it is where Sendspin and multi-room sync live, so it gives you the fullest experience. Music Assistant is free and open source, and it is an Open Home Foundation project. Without it, CAST-1 still works as a standard ESPHome media player in Home Assistant.

What cables do I need to buy? A USB-C cable, a USB-C power adapter, and a 3.5mm audio cable. The box contains CAST-1 only. If your amplifier takes RCA rather than 3.5mm, you will want a 3.5mm to RCA cable.

Can I use more than one? Yes. Multiple CAST-1 units synchronize through Sendspin in Music Assistant for whole-home audio. Bear in mind that Sendspin is a technical preview and still evolving.

Is Sendspin stable yet? It is a technical preview. It works today and improves steadily, but it is not finished. We would rather say that plainly than have you find out after buying.

Will it work with my old receiver? If it has a 3.5mm input, or an RCA input and you use an adapter cable, yes. Reviving older gear is one of our favorite things people do with these.

Does it need the cloud or an account? No. Everything runs locally on your own network. No cloud, no account, no subscription, and the firmware is open source.

If it sounds useful

CAST-1 is a small board that solves one problem: the speakers you already own are not on your network, and replacing them would be a waste of good equipment.

If you have gear worth keeping, that might be enough.

Apollo Automation is a commercial partner of the Open Home Foundation, and CAST-1 runs on ESPHome, the open source firmware project the foundation stewards.

Apollo Automation designs, engineers, and manufactures privacy-first, locally-controlled smart home sensors in Versailles, Kentucky. Every product features 100% local control with no cloud dependencies or subscriptions required. Apollo is a Works With Home Assistant partner, Made For ESPHome certified, Works With Homey certified, a BBB Accredited Business, and the second official commercial partner of the Open Home Foundation. Learn more at apolloautomation.com.

#ApolloAutomation #CAST1 #ESPHome #HomeAssistant #MusicAssistant #Sendspin #MultiRoomAudio #SmartHome #LocalControl #OpenSource #HiFi #NetworkAudio #DIYAudio

CAST-1, audio casting, network audio player, ESPHome media player, Music Assistant, Sendspin, multi-room audio, Home Assistant audio, PCM5122, DAC, ESP32-S3, 3.5mm streamer, smart speaker adapter, whole home audio, Bluetooth proxy, local control, open source audio, Apollo Automation, TTS announcements, hi-fi streaming

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