feat: Denkovi USB 4/8 (selectable) + generic USB-serial relay board (CH340/LCUS)

- Denkovi (FT245 D2XX) now selectable as 4 or 8 relays (a 4-relay board just uses
  the low nibble); NewDenkovi takes a count, driven by the device's Channels.
- New 'usbrelay' backend: cheap CH340/LCUS USB-serial boards over a COM port
  using the common A0 protocol ([0xA0][relay][state][checksum]); write-only, so
  Status is a shadow. Channel count configurable (1/2/4/8/16).
- StationDevice gains Channels; deviceRelayCount() drives label/relay counts for
  the variable-size types. Device editor: channel selector + COM-port picker
  (usbrelay) / FTDI-serial (denkovi).

Both untested on hardware; the A0 command set / Denkovi bit order may need a tweak
after a live test.

app.go

@@ -11397,14 +11397,28 @@ func boolStr(b bool) string {
 // StationDevice is one configured relay board for the Station Control tab.
 type StationDevice struct {
 	ID     string   `json:"id"`
-	Type   string   `json:"type"` // "webswitch" | "kmtronic" | "denkovi"
+	Type   string   `json:"type"` // "webswitch" | "kmtronic" | "denkovi" | "usbrelay"
 	Name   string   `json:"name"`
-	Host   string   `json:"host"`
+	Host   string   `json:"host"` // IP for network boards; FTDI serial for denkovi; COM port for usbrelay
 	User   string   `json:"user,omitempty"` // KMTronic HTTP auth (blank = none)
 	Pass   string   `json:"pass,omitempty"`
+	Channels int    `json:"channels,omitempty"` // usbrelay only: number of relays (1/2/4/8/16)
 	Labels []string `json:"labels"` // per-relay label (index 0 = relay 1)
 }
 
+// deviceRelayCount is the relay count for a configured device — fixed by type,
+// except the Denkovi (4 or 8) and the generic USB-serial board, whose channel
+// count the user picks.
+func deviceRelayCount(d StationDevice) int {
+	if d.Type == "usbrelay" || d.Type == "denkovi" {
+		if d.Channels >= 1 {
+			return d.Channels
+		}
+		return 8
+	}
+	return relayCountFor(d.Type)
+}
+
 // relayCountFor returns a device type's fixed relay count.
 func relayCountFor(typ string) int {
 	switch typ {
@@ -11422,7 +11436,10 @@ func deviceDriver(d StationDevice) relaydev.Device {
 		return relaydev.NewKMTronic(d.Host, d.User, d.Pass)
 	case "denkovi":
 		// Host carries the FTDI serial number (e.g. "DAE0006K"), not a hostname.
-		return relaydev.NewDenkovi(d.Host)
+		return relaydev.NewDenkovi(d.Host, deviceRelayCount(d))
+	case "usbrelay":
+		// Host carries the COM port (e.g. "COM5"); CH340/LCUS "A0" serial protocol.
+		return relaydev.NewSerialRelay(d.Host, deviceRelayCount(d))
 	default:
 		return relaydev.NewWebswitch(d.Host)
 	}
@@ -11458,7 +11475,7 @@ func (a *App) SaveStationDevices(devs []StationDevice) error {
 	}
 	for i := range devs {
 		switch devs[i].Type {
-		case "kmtronic", "denkovi", "webswitch":
+		case "kmtronic", "denkovi", "usbrelay", "webswitch":
 			// known type — keep
 		default:
 			devs[i].Type = "webswitch"
@@ -11466,7 +11483,7 @@ func (a *App) SaveStationDevices(devs []StationDevice) error {
 		if strings.TrimSpace(devs[i].ID) == "" {
 			devs[i].ID = fmt.Sprintf("dev%d-%d", i, time.Now().UnixNano())
 		}
-		n := relayCountFor(devs[i].Type)
+		n := deviceRelayCount(devs[i])
 		for len(devs[i].Labels) < n {
 			devs[i].Labels = append(devs[i].Labels, "")
 		}
@@ -11507,7 +11524,7 @@ func (a *App) GetStationStatus() []StationDeviceStatus {
 		go func(i int) {
 			defer wg.Done()
 			d := devs[i]
-			n := relayCountFor(d.Type)
+			n := deviceRelayCount(d)
 			ds := StationDeviceStatus{ID: d.ID, Name: d.Name, Type: d.Type}
 			ctx, cancel := context.WithTimeout(a.ctx, 6*time.Second)
 			defer cancel()

frontend/src/components/SettingsModal.tsx

@@ -698,7 +698,7 @@ function RelayAutoPanel() {
         <div key={dev.id} className="rounded-md border border-border">
           <div className="px-3 py-1.5 border-b border-border bg-muted/40 text-xs font-semibold">{dev.name || dev.id}</div>
           <div className="divide-y divide-border/60">
-            {Array.from({ length: relayCountUI(dev.type) }, (_, i) => i + 1).map((relay) => {
+            {Array.from({ length: (dev.labels?.length || relayCountUI(dev.type)) }, (_, i) => i + 1).map((relay) => {
               const r = ruleFor(dev.id, relay);
               const label = (dev.labels?.[relay - 1] || '').trim() || `${t('relayauto.relay')} ${relay}`;
               return (

frontend/src/components/StationControlPanel.tsx

@@ -12,17 +12,22 @@ import {
   GetStationDevices, SaveStationDevices, GetStationStatus, StationSetRelay,
   GetRotatorHeading, RotatorGoTo, RotatorStop,
   GetUltrabeamStatus, SetUltrabeamDirection, UltrabeamRetract, MotorSetElement, MotorReadElements,
-  ListDenkoviDevices,
+  ListDenkoviDevices, ListSerialPorts,
 } from '../../wailsjs/go/main/App';
 
 type RotatorProps = { centerLat?: number | null; centerLon?: number | null; bearing?: number | null };
 
-type Device = { id: string; type: string; name: string; host: string; user?: string; pass?: string; labels: string[] };
+type Device = { id: string; type: string; name: string; host: string; user?: string; pass?: string; channels?: number; labels: string[] };
 type Relay = { number: number; label: string; on: boolean };
 type DevStatus = { id: string; name: string; type: string; connected: boolean; error?: string; relays: Relay[] };
 
-const RELAY_COUNT: Record<string, number> = { webswitch: 5, kmtronic: 8, denkovi: 8 };
+const RELAY_COUNT: Record<string, number> = { webswitch: 5, kmtronic: 8, denkovi: 8, usbrelay: 8 };
-const TYPE_LABEL: Record<string, string> = { webswitch: 'WebSwitch 1216H', kmtronic: 'KMTronic 8-relay', denkovi: 'Denkovi USB 8-relay' };
+const TYPE_LABEL: Record<string, string> = { webswitch: 'WebSwitch 1216H', kmtronic: 'KMTronic 8-relay', denkovi: 'Denkovi USB relay', usbrelay: 'USB serial relay' };
+
+// Relay count for a configured device: fixed by type, except Denkovi (4/8) and
+// the generic USB-serial board, whose channel count the user picks.
+const chanCount = (d: Device): number =>
+  (d.type === 'denkovi' || d.type === 'usbrelay') ? (d.channels && d.channels >= 1 ? d.channels : 8) : (RELAY_COUNT[d.type] ?? 5);
 
 function blankDevice(): Device {
   return { id: '', type: 'webswitch', name: '', host: '', user: '', pass: '', labels: Array(5).fill('') };
@@ -446,12 +451,25 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
   const ref = useRef<HTMLDivElement>(null);
   useEffect(() => { ref.current?.scrollIntoView({ behavior: 'smooth', block: 'nearest' }); }, []);
   const setType = (type: string) => {
-    const n = RELAY_COUNT[type] ?? 5;
+    const channels = (type === 'denkovi' || type === 'usbrelay') ? (device.channels || 8) : undefined;
+    const n = chanCount({ ...device, type, channels });
     const labels = Array.from({ length: n }, (_, i) => device.labels[i] ?? '');
-    onChange({ ...device, type, labels });
+    onChange({ ...device, type, channels, labels });
+  };
+  const setChannels = (channels: number) => {
+    const n = chanCount({ ...device, channels });
+    const labels = Array.from({ length: n }, (_, i) => device.labels[i] ?? '');
+    onChange({ ...device, channels, labels });
   };
   const isKM = device.type === 'kmtronic';
   const isDenkovi = device.type === 'denkovi';
+  const isUsbRelay = device.type === 'usbrelay';
+  // COM ports for the generic USB-serial relay picker.
+  const [serialPorts, setSerialPorts] = useState<string[]>([]);
+  useEffect(() => {
+    if (!isUsbRelay) return;
+    ListSerialPorts().then((p) => setSerialPorts((p ?? []) as string[])).catch(() => setSerialPorts([]));
+  }, [isUsbRelay]);
   // Detected FTDI serials for the Denkovi picker.
   const [denkoviSerials, setDenkoviSerials] = useState<string[]>([]);
   const [detecting, setDetecting] = useState(false);
@@ -477,7 +495,8 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
             <SelectContent>
               <SelectItem value="webswitch">WebSwitch 1216H (5 relays)</SelectItem>
               <SelectItem value="kmtronic">KMTronic 8-relay (LAN)</SelectItem>
-              <SelectItem value="denkovi">Denkovi USB 8-relay (FT245)</SelectItem>
+              <SelectItem value="denkovi">Denkovi USB relay (FT245, 4/8)</SelectItem>
+              <SelectItem value="usbrelay">USB serial relay (CH340/LCUS)</SelectItem>
             </SelectContent>
           </Select>
         </div>
@@ -486,6 +505,19 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
           <Input value={device.name} placeholder={TYPE_LABEL[device.type]} onChange={(e) => onChange({ ...device, name: e.target.value })} />
         </div>
       </div>
+      {(isDenkovi || isUsbRelay) && (
+        <div className="space-y-1 max-w-[10rem]">
+          <Label>{t('station.channels')}</Label>
+          <Select value={String(chanCount(device))} onValueChange={(v) => setChannels(parseInt(v, 10))}>
+            <SelectTrigger className="h-9"><SelectValue /></SelectTrigger>
+            <SelectContent>
+              {(isDenkovi ? [4, 8] : [1, 2, 4, 8, 16]).map((n) => (
+                <SelectItem key={n} value={String(n)}>{n}</SelectItem>
+              ))}
+            </SelectContent>
+          </Select>
+        </div>
+      )}
       {isDenkovi ? (
         <div className="space-y-1 max-w-md">
           <Label>{t('station.ftdiSerial')}</Label>
@@ -503,6 +535,23 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
           </div>
           <p className="text-[10px] text-muted-foreground">{t('station.ftdiHint')}</p>
         </div>
+      ) : isUsbRelay ? (
+        <div className="space-y-1 max-w-md">
+          <Label>{t('station.comPort')}</Label>
+          <div className="flex items-center gap-2">
+            <Select value={device.host || '_'} onValueChange={(v) => onChange({ ...device, host: v === '_' ? '' : v })}>
+              <SelectTrigger className="h-9 flex-1"><SelectValue placeholder="— COM —" /></SelectTrigger>
+              <SelectContent>
+                {serialPorts.length === 0 && <SelectItem value="_" disabled>{t('station.noPorts')}</SelectItem>}
+                {serialPorts.map((p) => <SelectItem key={p} value={p}>{p}</SelectItem>)}
+              </SelectContent>
+            </Select>
+            <Button size="sm" variant="outline" onClick={() => ListSerialPorts().then((p) => setSerialPorts((p ?? []) as string[])).catch(() => {})}>
+              <RefreshCw className="size-3.5" />
+            </Button>
+          </div>
+          <p className="text-[10px] text-muted-foreground">{t('station.usbRelayHint')}</p>
+        </div>
       ) : (
       <div className={cn('grid gap-3', isKM ? 'grid-cols-3' : 'grid-cols-1')}>
         <div className={cn('space-y-1', isKM ? '' : 'max-w-xs')}>

frontend/src/lib/i18n.tsx

@@ -131,7 +131,7 @@ const en: Dict = {
   'uscty.backfillIntro': 'Resolve county (and grid) for US QSOs already in your log that are missing them. Existing values are kept — only blanks are filled.',
   'uscty.backfillRun': 'Fill missing counties',
   'uscty.backfillDone': '{s} US QSOs scanned · {c} counties, {g} grids filled.',
-  'station.title': 'Station Control', 'station.rotator': 'Rotator', 'station.rotatorNoRead': 'No heading read', 'station.pattern': 'Pattern', 'station.bi': 'Bi', 'station.retract': 'Retract elements', 'station.moving': 'MOVING', 'station.elements': 'Elements (mm)', 'station.read': 'Read', 'station.readLengths': 'Read current element lengths from the controller', 'station.noLengths': 'Lengths unknown — click Read to fetch them from the controller.', 'station.element': 'Element', 'station.reflector': 'Reflector', 'station.driven': 'Driven', 'station.director': 'Dir', 'station.set': 'Set', 'station.elementsHint': 'Each press lengthens/shortens the element by 2 mm (like the physical console). Verify which element responds on your antenna.', 'station.setExactLen': 'Click to type the exact current length (fixes the baseline if the auto-read is off).', 'station.atMax': 'Controller refused — the element is likely at its maximum length for this band, so it can\'t extend further.', 'station.go': 'Go', 'station.stop': 'Stop', 'station.dragHint': 'Drag a widget by its card to reorder. Pick a column count to lay them out in a grid.', 'station.colsAuto': 'Auto', 'station.addDevice': 'Add device', 'station.editDevice': 'Edit device', 'station.empty': 'No relay boards yet. Add a WebSwitch 1216H or a KMTronic 8-relay board to control your station power and accessories.', 'station.online': 'Online', 'station.offline': 'Offline', 'station.edit': 'Edit', 'station.delete': 'Delete', 'station.relay': 'Relay', 'station.on': 'ON', 'station.off': 'OFF', 'station.type': 'Device type', 'station.name': 'Name', 'station.host': 'Host / IP', 'station.user': 'Username', 'station.pass': 'Password', 'station.optional': 'optional', 'station.ftdiSerial': 'FTDI serial number', 'station.detect': 'Detect', 'station.ftdiHint': 'The Denkovi board is driven via FTDI bit-bang (not the COM port). Pick its serial (e.g. DAE0006K). Needs the FTDI D2XX driver installed.', 'station.labels': 'Relay labels', 'station.cancel': 'Cancel', 'station.save': 'Save',
+  'station.title': 'Station Control', 'station.rotator': 'Rotator', 'station.rotatorNoRead': 'No heading read', 'station.pattern': 'Pattern', 'station.bi': 'Bi', 'station.retract': 'Retract elements', 'station.moving': 'MOVING', 'station.elements': 'Elements (mm)', 'station.read': 'Read', 'station.readLengths': 'Read current element lengths from the controller', 'station.noLengths': 'Lengths unknown — click Read to fetch them from the controller.', 'station.element': 'Element', 'station.reflector': 'Reflector', 'station.driven': 'Driven', 'station.director': 'Dir', 'station.set': 'Set', 'station.elementsHint': 'Each press lengthens/shortens the element by 2 mm (like the physical console). Verify which element responds on your antenna.', 'station.setExactLen': 'Click to type the exact current length (fixes the baseline if the auto-read is off).', 'station.atMax': 'Controller refused — the element is likely at its maximum length for this band, so it can\'t extend further.', 'station.go': 'Go', 'station.stop': 'Stop', 'station.dragHint': 'Drag a widget by its card to reorder. Pick a column count to lay them out in a grid.', 'station.colsAuto': 'Auto', 'station.addDevice': 'Add device', 'station.editDevice': 'Edit device', 'station.empty': 'No relay boards yet. Add a WebSwitch 1216H or a KMTronic 8-relay board to control your station power and accessories.', 'station.online': 'Online', 'station.offline': 'Offline', 'station.edit': 'Edit', 'station.delete': 'Delete', 'station.relay': 'Relay', 'station.on': 'ON', 'station.off': 'OFF', 'station.type': 'Device type', 'station.name': 'Name', 'station.host': 'Host / IP', 'station.user': 'Username', 'station.pass': 'Password', 'station.optional': 'optional', 'station.ftdiSerial': 'FTDI serial number', 'station.detect': 'Detect', 'station.ftdiHint': 'The Denkovi board is driven via FTDI bit-bang (not the COM port). Pick its serial (e.g. DAE0006K). Needs the FTDI D2XX driver installed.', 'station.channels': 'Relays', 'station.comPort': 'COM port', 'station.noPorts': 'No ports found', 'station.usbRelayHint': 'Cheap USB-serial relay boards (CH340/LCUS) using the A0 command protocol. If yours does not switch, tell me its model / command set.', 'station.labels': 'Relay labels', 'station.cancel': 'Cancel', 'station.save': 'Save',
   'sec.awards': 'Awards', 'sec.cat': 'CAT interface', 'sec.rotator': 'Rotator', 'sec.winkeyer': 'CW Keyer',
   'sec.antenna': 'Ultrabeam / Steppir', 'sec.antgenius': 'Antenna Genius', 'sec.pgxl': 'Power Genius', 'sec.flex': 'FlexRadio', 'sec.audio': 'Audio devices',
   'sec.relayauto': 'Relay auto-control',
@@ -444,7 +444,7 @@ const fr: Dict = {
   'uscty.backfillIntro': "Résout le comté (et le locator) pour les QSO US déjà dans ton log qui n'en ont pas. Les valeurs existantes sont conservées — seuls les vides sont remplis.",
   'uscty.backfillRun': 'Remplir les comtés manquants',
   'uscty.backfillDone': '{s} QSO US analysés · {c} comtés, {g} locators remplis.',
-  'station.title': 'Contrôle station', 'station.rotator': 'Rotator', 'station.rotatorNoRead': 'Azimut non lu', 'station.pattern': 'Diagramme', 'station.bi': 'Bi', 'station.retract': 'Rétracter les éléments', 'station.moving': 'EN MOUVEMENT', 'station.elements': 'Éléments (mm)', 'station.read': 'Lire', 'station.readLengths': 'Lire les longueurs actuelles depuis le contrôleur', 'station.noLengths': 'Longueurs inconnues — clique sur Lire pour les récupérer depuis le contrôleur.', 'station.element': 'Élément', 'station.reflector': 'Réflecteur', 'station.driven': 'Radiateur', 'station.director': 'Dir', 'station.set': 'Régler', 'station.elementsHint': "Chaque appui allonge/raccourcit l'élément de 2 mm (comme le pupitre). Vérifie quel élément répond sur ton antenne.", 'station.setExactLen': "Clique pour taper la longueur actuelle exacte (recale la base si la lecture auto est fausse).", 'station.atMax': "Refusé par le contrôleur — l'élément est probablement en butée (longueur max pour cette bande), il ne peut plus s'allonger.", 'station.go': 'Aller', 'station.stop': 'Stop', 'station.dragHint': 'Glisse une carte pour réordonner. Choisis un nombre de colonnes pour la disposition.', 'station.colsAuto': 'Auto', 'station.addDevice': 'Ajouter un appareil', 'station.editDevice': "Modifier l'appareil", 'station.empty': "Aucune carte relais. Ajoute un WebSwitch 1216H ou une carte KMTronic 8 relais pour piloter l'alimentation et les accessoires de ta station.", 'station.online': 'En ligne', 'station.offline': 'Hors ligne', 'station.edit': 'Modifier', 'station.delete': 'Supprimer', 'station.relay': 'Relais', 'station.on': 'ON', 'station.off': 'OFF', 'station.type': "Type d'appareil", 'station.name': 'Nom', 'station.host': 'Hôte / IP', 'station.user': "Nom d'utilisateur", 'station.pass': 'Mot de passe', 'station.optional': 'optionnel', 'station.ftdiSerial': 'Numéro de série FTDI', 'station.detect': 'Détecter', 'station.ftdiHint': "La carte Denkovi se pilote en FTDI bit-bang (pas via le port COM). Choisis son numéro de série (ex. DAE0006K). Nécessite le driver FTDI D2XX installé.", 'station.labels': 'Libellés des relais', 'station.cancel': 'Annuler', 'station.save': 'Enregistrer',
+  'station.title': 'Contrôle station', 'station.rotator': 'Rotator', 'station.rotatorNoRead': 'Azimut non lu', 'station.pattern': 'Diagramme', 'station.bi': 'Bi', 'station.retract': 'Rétracter les éléments', 'station.moving': 'EN MOUVEMENT', 'station.elements': 'Éléments (mm)', 'station.read': 'Lire', 'station.readLengths': 'Lire les longueurs actuelles depuis le contrôleur', 'station.noLengths': 'Longueurs inconnues — clique sur Lire pour les récupérer depuis le contrôleur.', 'station.element': 'Élément', 'station.reflector': 'Réflecteur', 'station.driven': 'Radiateur', 'station.director': 'Dir', 'station.set': 'Régler', 'station.elementsHint': "Chaque appui allonge/raccourcit l'élément de 2 mm (comme le pupitre). Vérifie quel élément répond sur ton antenne.", 'station.setExactLen': "Clique pour taper la longueur actuelle exacte (recale la base si la lecture auto est fausse).", 'station.atMax': "Refusé par le contrôleur — l'élément est probablement en butée (longueur max pour cette bande), il ne peut plus s'allonger.", 'station.go': 'Aller', 'station.stop': 'Stop', 'station.dragHint': 'Glisse une carte pour réordonner. Choisis un nombre de colonnes pour la disposition.', 'station.colsAuto': 'Auto', 'station.addDevice': 'Ajouter un appareil', 'station.editDevice': "Modifier l'appareil", 'station.empty': "Aucune carte relais. Ajoute un WebSwitch 1216H ou une carte KMTronic 8 relais pour piloter l'alimentation et les accessoires de ta station.", 'station.online': 'En ligne', 'station.offline': 'Hors ligne', 'station.edit': 'Modifier', 'station.delete': 'Supprimer', 'station.relay': 'Relais', 'station.on': 'ON', 'station.off': 'OFF', 'station.type': "Type d'appareil", 'station.name': 'Nom', 'station.host': 'Hôte / IP', 'station.user': "Nom d'utilisateur", 'station.pass': 'Mot de passe', 'station.optional': 'optionnel', 'station.ftdiSerial': 'Numéro de série FTDI', 'station.detect': 'Détecter', 'station.ftdiHint': "La carte Denkovi se pilote en FTDI bit-bang (pas via le port COM). Choisis son numéro de série (ex. DAE0006K). Nécessite le driver FTDI D2XX installé.", 'station.channels': 'Relais', 'station.comPort': 'Port COM', 'station.noPorts': 'Aucun port', 'station.usbRelayHint': "Cartes USB-série bon marché (CH340/LCUS) protocole A0. Si la tienne ne commute pas, donne-moi le modèle / jeu de commandes.", 'station.labels': 'Libellés des relais', 'station.cancel': 'Annuler', 'station.save': 'Enregistrer',
   'sec.awards': 'Diplômes', 'sec.cat': 'Interface CAT', 'sec.rotator': 'Rotator', 'sec.winkeyer': 'Manipulateur CW',
   'sec.antenna': 'Antenne motorisée', 'sec.antgenius': 'Antenna Genius', 'sec.pgxl': 'Power Genius', 'sec.flex': 'FlexRadio', 'sec.audio': 'Périphériques audio',
   'sec.relayauto': 'Relais automatiques',

frontend/wailsjs/go/models.ts

@@ -2600,6 +2600,7 @@ export namespace main {
 	    host: string;
 	    user?: string;
 	    pass?: string;
+	    channels?: number;
 	    labels: string[];
 	
 	    static createFrom(source: any = {}) {
@@ -2614,6 +2615,7 @@ export namespace main {
 	        this.host = source["host"];
 	        this.user = source["user"];
 	        this.pass = source["pass"];
+	        this.channels = source["channels"];
 	        this.labels = source["labels"];
 	    }
 	}

internal/relaydev/denkovi_other.go

@@ -10,12 +10,17 @@ import (
 	"fmt"
 )
 
-type denkoviStub struct{}
+type denkoviStub struct{ count int }
 
 // NewDenkovi returns a stub on non-Windows builds.
-func NewDenkovi(serial string) Device { return denkoviStub{} }
+func NewDenkovi(serial string, count int) Device {
+	if count != 4 {
+		count = 8
+	}
+	return denkoviStub{count: count}
+}
 
-func (denkoviStub) Count() int { return 8 }
+func (s denkoviStub) Count() int { return s.count }
 func (denkoviStub) Status(context.Context) ([]bool, error) {
 	return nil, fmt.Errorf("Denkovi USB relay board is only supported on Windows")
 }

internal/relaydev/denkovi_windows.go

@@ -46,10 +46,14 @@ type denkovi struct {
 	opened bool
 }
 
-// NewDenkovi builds a driver for a Denkovi USB 8-relay board identified by its
+// NewDenkovi builds a driver for a Denkovi USB relay board (4 or 8 relays)
-// FTDI serial number (shown by the vendor tool / FT_PROG, e.g. "DAE0006K").
+// identified by its FTDI serial number (shown by the vendor tool / FT_PROG,
-func NewDenkovi(serial string) Device {
+// e.g. "DAE0006K"). count defaults to 8; a 4-relay board just uses the low 4 bits.
-	return &denkovi{serial: strings.TrimSpace(serial), count: 8}
+func NewDenkovi(serial string, count int) Device {
+	if count != 4 && count != 8 {
+		count = 8
+	}
+	return &denkovi{serial: strings.TrimSpace(serial), count: count}
 }
 
 func (d *denkovi) Count() int { return d.count }

internal/relaydev/serialrelay.go

@@ -0,0 +1,89 @@
+package relaydev
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"sync"
+
+	"go.bug.st/serial"
+)
+
+// serialRelay drives the common cheap USB-serial relay boards (CH340 / LCUS-1
+// style) that use the "A0" command protocol over a virtual COM port:
+//
+//	[0xA0] [relay 1-based] [state 0|1] [checksum]     checksum = (0xA0+relay+state) & 0xFF
+//
+// e.g. relay 1 ON = A0 01 01 A2, relay 1 OFF = A0 01 00 A1. These boards are
+// write-only (no state readback), so Status reflects a shadow of what we sent.
+// Channel count varies by board (1/2/4/8/16), so it is configurable.
+type serialRelay struct {
+	portName string
+	count    int
+	baud     int
+	mu       sync.Mutex
+	port     serial.Port
+	shadow   []bool
+}
+
+// NewSerialRelay builds a driver for a CH340/LCUS-style USB-serial relay board on
+// the given COM port with `count` channels (defaults to 8).
+func NewSerialRelay(port string, count int) Device {
+	if count < 1 {
+		count = 8
+	}
+	return &serialRelay{portName: strings.TrimSpace(port), count: count, baud: 9600, shadow: make([]bool, count)}
+}
+
+func (s *serialRelay) Count() int { return s.count }
+
+func (s *serialRelay) ensureOpen() error {
+	if s.port != nil {
+		return nil
+	}
+	if s.portName == "" {
+		return fmt.Errorf("no COM port set for the USB relay board")
+	}
+	p, err := serial.Open(s.portName, &serial.Mode{BaudRate: s.baud})
+	if err != nil {
+		return fmt.Errorf("open %s: %w", s.portName, err)
+	}
+	s.port = p
+	return nil
+}
+
+func (s *serialRelay) Set(ctx context.Context, relay int, on bool) error {
+	if relay < 1 || relay > s.count {
+		return fmt.Errorf("relay %d out of range 1..%d", relay, s.count)
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if err := s.ensureOpen(); err != nil {
+		return err
+	}
+	st := byte(0)
+	if on {
+		st = 1
+	}
+	r := byte(relay)
+	frame := []byte{0xA0, r, st, byte(0xA0) + r + st} // last byte = checksum
+	if _, err := s.port.Write(frame); err != nil {
+		// Drop the handle so the next call reopens (USB unplugged / port reset).
+		s.port.Close()
+		s.port = nil
+		return fmt.Errorf("write to %s: %w", s.portName, err)
+	}
+	s.shadow[relay-1] = on
+	return nil
+}
+
+func (s *serialRelay) Status(ctx context.Context) ([]bool, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if err := s.ensureOpen(); err != nil {
+		return nil, err
+	}
+	out := make([]bool, s.count)
+	copy(out, s.shadow)
+	return out, nil
+}