Add photos and datasheet; correct wiring and protocol docs
The 20L203 input is RS-232 (reference build uses a MAX3232), it runs on 5-24 V, and it boots in non-scrolling overwrite mode. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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# Samsung serial VFD — ESPHome component
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An ESPHome external component for the Samsung 2-line × 20-character serial VFD
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(vacuum fluorescent display) that takes 5 V TTL serial at 9600 baud, 8N1.
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An ESPHome external component for the Samsung 20L203 2-line × 20-character VFD
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(vacuum fluorescent display) pole display, driven over a single serial wire at
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9600 baud.
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It keeps a copy of the screen in RAM and only sends data when something
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changes. Updates overwrite the screen in place instead of clearing it first,
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so the clock doesn't flicker.
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<p>
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<img src="docs/front.jpg" alt="Front of the display" height="300">
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<img src="docs/back.jpg" alt="Back of the controller board" height="300">
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</p>
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```
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components/samsung_vfd/ the component (Python schema + C++)
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examples/samsung-vfd.yaml full example: clock + two Home Assistant text entities
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examples/secrets.yaml.example
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docs/ photos and the 20L203DA12 datasheet
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```
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## Using it from your ESPHome server
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@@ -43,24 +50,70 @@ into your ESPHome config folder. Add the keys from
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[examples/secrets.yaml.example](examples/secrets.yaml.example) to your
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`secrets.yaml`.
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## Wiring
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## Hardware
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The component only sends to the display. The ESP32's 3.3 V output is enough for
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most 5 V TTL inputs. ESP32 GPIOs are **not** 5 V tolerant, so never connect the
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display's TX back to the ESP32 without a level shifter or divider.
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The board in the photos is a 20L203DA5 (rev A). The included
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[datasheet](docs/20L203DA12-datasheet.pdf) is for the 20L203DA12, a variant
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with the same command set.
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| Display | ESP32 |
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|---------|-------|
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| RX | GPIO17 (UART TX) |
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| GND | GND |
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| 5 V | external 5 V supply |
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### Connector (3-pin Molex 5046-03A)
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The display draws more current than a dev-board regulator can comfortably
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supply. Power it from its own supply and connect the grounds together.
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| Pin | Signal | Connect to |
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|-----|--------|------------|
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| 1 | VCC | 5–24 V DC supply |
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| 2 | RXD | MAX3232 T1OUT (T1IN ← ESP32 GPIO17), see below |
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| 3 | GND | supply GND, MAX3232 GND **and** ESP32 GND |
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To use GPIO1 (TX0, shared with USB logging), set `tx_pin: GPIO1` and
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`logger: baud_rate: 0` so log output doesn't end up on the display. If the
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display stays blank at 3.3 V levels, add a 74HCT125 or similar level shifter.
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### Power
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The display takes 5–24 V. At 5 V it draws about 0.8 A typical and 1.2 A
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maximum, and the inrush current at power-on can be up to five times that. A
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dev-board regulator can't supply this, so give the display its own supply,
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for example 12 V at 1 A, and connect the grounds together.
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### Signal levels
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The RXD input goes through an RS-232 receiver: it expects ±3 to ±15 V and
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idles at the negative level (mark). It tolerates ±30 V, so a 3.3 V ESP32 pin
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can't damage it. There are two ways to connect it:
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- **Through a MAX3232 (recommended, and how the original build is wired).**
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Power the MAX3232 from the ESP32's 3.3 V, then wire GPIO17 → T1IN and
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T1OUT → display RXD. The MAX3232 produces real RS-232 levels and does the
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inversion itself, so use the plain `tx_pin: GPIO17`.
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- **Direct from the ESP32.** A plain TTL signal arrives inverted, so wire
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GPIO17 straight to RXD and invert the pin in the UART config:
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```yaml
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uart:
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id: uart_vfd
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tx_pin:
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number: GPIO17
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inverted: true
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baud_rate: 9600
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```
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This relies on the receiver's switching threshold, which on most RS-232
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receivers is around 1.3 V. It isn't guaranteed by the spec, which asks for
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at least 3 V.
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If the display shows garbage or nothing at all, the inversion setting is the
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first thing to check: off with a MAX3232, on without one.
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### Jumpers
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The 2×8 pin header on the board selects the following. All jumpers open is the
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factory default.
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| Jumpers | Setting | Default (open) |
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|---------|---------|----------------|
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| 1, 2 | baud rate: 9600 / 4800 / 2400 / 19200 | 9600 |
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| 3, 4 | parity: none / odd / even | none |
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| 5 | self-test at power-on | off |
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| 6, 7, 8 | font for codes 0x80–0xFF | PC437 |
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This component expects 9600 baud and no parity, which ESPHome's UART uses by
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default.
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## Configuration
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@@ -70,7 +123,7 @@ samsung_vfd:
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uart_id: uart_vfd
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cols: 20 # default 20 (1–80)
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rows: 2 # default 2 (1–8)
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send_newlines: false # default false; send CR LF between lines
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send_newlines: false # default false; leave off for this display
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```
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The UART must be 9600 baud with a `tx_pin`. The component requires a `time:`
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@@ -121,26 +174,30 @@ characters become spaces.
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## Protocol
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These are the commands the component uses. The datasheet, section 5.4, lists
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the rest, including cursor positioning, brightness, blinking and the
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annunciator triangles.
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| Bytes | Effect |
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|-------|--------|
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| `1B 40` (`ESC @`) | init / reset |
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| `0C` | clear screen |
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| `0B` | cursor home |
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| text | printed at the cursor; wraps to the next line by itself |
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| `1B 40` (`ESC @`) | initialise: reset settings, clear, cursor home |
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| `0C` | clear screen, cursor home |
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| `0B` | cursor home (top-left) |
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| `20`–`FF` | print a character and move the cursor right |
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Each update sends `0B` (home) followed by both lines, each padded to exactly
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`cols` characters.
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At power-on the display is in overwrite mode. After the last column of the top
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line the cursor continues on the bottom line, and after the last column of the
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bottom line it goes back to the top-left. Nothing scrolls. Each update
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therefore sends `0B` (home) followed by both lines, each padded to exactly 20
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characters.
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## Troubleshooting
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- **Line 2 lands on the wrong row, or text runs together:** try
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`send_newlines: true`.
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- **The screen scrolls up a line after each update:** the display scrolls as
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soon as the last cell is written. Use `cols: 19` together with
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`send_newlines: true`.
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- **A stray character appears top-left:** the display doesn't treat `0B` as
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home. Change `CMD_HOME` in
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[samsung_vfd.h](components/samsung_vfd/samsung_vfd.h).
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- **Garbled characters:** check that `uart:` is at 9600 baud and that the
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display takes 5 V TTL levels, not RS-232 levels. A real RS-232 input needs a
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MAX232 inverter.
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- **Garbage or nothing on the display:** toggle `inverted:` on the TX pin (see
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[Signal levels](#signal-levels)). Check that the baud jumpers 1 and 2 are
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open (9600) and that parity jumpers 3 and 4 are open (none).
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- **The display runs its self-test for about 20 s after power-on:** jumper 5 is
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shorted.
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- **Line 2 text lands on line 1:** make sure `send_newlines` is off. With
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20-column lines the cursor has already wrapped to line 2, and an extra line
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feed sends it back to line 1.
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