feat: Denkovi USB 8-relay board (FT245 D2XX bit-bang)

Third relay device alongside WebSwitch and KMTronic. Despite enumerating as a
COM port, this board is driven via FTDI D2XX synchronous bit-bang (one byte = 8
relays, bit 0 = relay 1), not serial ASCII — so we load ftd2xx.dll at runtime
(no CGO) and call FT_OpenEx/FT_SetBitMode/FT_Write, addressing the board by its
FTDI serial (e.g. DAE0006K), exactly like the vendor tool. Windows-only (stub
elsewhere); ListDenkoviDevices enumerates connected serials for the picker.

Wired into relaydev (Count/Status/Set), app.go (deviceDriver/relayCountFor/type
whitelist + ListDenkoviDevices binding), and the Station device editor (new type
+ FTDI-serial field with Detect). Untested on hardware; bit order / on-polarity
may need a flip after a live test.

app.go

@@ -11397,7 +11397,7 @@ 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"
+	Type   string   `json:"type"` // "webswitch" | "kmtronic" | "denkovi"
 	Name   string   `json:"name"`
 	Host   string   `json:"host"`
 	User   string   `json:"user,omitempty"` // KMTronic HTTP auth (blank = none)
@@ -11407,19 +11407,32 @@ type StationDevice struct {
 
 // relayCountFor returns a device type's fixed relay count.
 func relayCountFor(typ string) int {
-	if typ == "kmtronic" {
+	switch typ {
+	case "kmtronic", "denkovi":
 		return 8
-	}
+	default:
 		return 5 // webswitch 1216H
 	}
+}
 
 // deviceDriver builds the wire driver for a configured device.
 func deviceDriver(d StationDevice) relaydev.Device {
-	if d.Type == "kmtronic" {
+	switch d.Type {
+	case "kmtronic":
 		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)
+	default:
 		return relaydev.NewWebswitch(d.Host)
 	}
+}
+
+// ListDenkoviDevices returns the FTDI serial numbers of connected Denkovi/FTDI
+// boards, for the settings picker. Windows-only (FTDI D2XX).
+func (a *App) ListDenkoviDevices() ([]string, error) {
+	return relaydev.ListDenkovi()
+}
 
 // GetStationDevices returns the configured relay boards (without live state).
 func (a *App) GetStationDevices() []StationDevice {
@@ -11444,7 +11457,10 @@ func (a *App) SaveStationDevices(devs []StationDevice) error {
 		return fmt.Errorf("db not initialized")
 	}
 	for i := range devs {
-		if devs[i].Type != "kmtronic" {
+		switch devs[i].Type {
+		case "kmtronic", "denkovi", "webswitch":
+			// known type — keep
+		default:
 			devs[i].Type = "webswitch"
 		}
 		if strings.TrimSpace(devs[i].ID) == "" {

frontend/src/components/SettingsModal.tsx

@@ -647,7 +647,7 @@ function ADIFMonitorPanel() {
 type RelayRuleUI = { device_id: string; relay: number; mode: string; freq_lo_khz: number; freq_hi_khz: number; bands: string[] };
 type StationDevUI = { id: string; type: string; name: string; labels: string[] };
 const RELAY_BANDS = ['160m', '80m', '60m', '40m', '30m', '20m', '17m', '15m', '12m', '10m', '6m', '4m', '2m', '70cm'];
-const relayCountUI = (type: string) => (type === 'kmtronic' ? 8 : 5);
+const relayCountUI = (type: string) => (type === 'kmtronic' || type === 'denkovi' ? 8 : 5);
 function RelayAutoPanel() {
   const { t } = useI18n();
   const [enabled, setEnabled] = useState(false);

frontend/src/components/StationControlPanel.tsx

@@ -12,6 +12,7 @@ import {
   GetStationDevices, SaveStationDevices, GetStationStatus, StationSetRelay,
   GetRotatorHeading, RotatorGoTo, RotatorStop,
   GetUltrabeamStatus, SetUltrabeamDirection, UltrabeamRetract, MotorSetElement, MotorReadElements,
+  ListDenkoviDevices,
 } from '../../wailsjs/go/main/App';
 
 type RotatorProps = { centerLat?: number | null; centerLon?: number | null; bearing?: number | null };
@@ -20,8 +21,8 @@ type Device = { id: string; type: string; name: string; host: string; user?: str
 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 };
+const RELAY_COUNT: Record<string, number> = { webswitch: 5, kmtronic: 8, denkovi: 8 };
-const TYPE_LABEL: Record<string, string> = { webswitch: 'WebSwitch 1216H', kmtronic: 'KMTronic 8-relay' };
+const TYPE_LABEL: Record<string, string> = { webswitch: 'WebSwitch 1216H', kmtronic: 'KMTronic 8-relay', denkovi: 'Denkovi USB 8-relay' };
 
 function blankDevice(): Device {
   return { id: '', type: 'webswitch', name: '', host: '', user: '', pass: '', labels: Array(5).fill('') };
@@ -450,6 +451,21 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
     onChange({ ...device, type, labels });
   };
   const isKM = device.type === 'kmtronic';
+  const isDenkovi = device.type === 'denkovi';
+  // Detected FTDI serials for the Denkovi picker.
+  const [denkoviSerials, setDenkoviSerials] = useState<string[]>([]);
+  const [detecting, setDetecting] = useState(false);
+  const detectDenkovi = async () => {
+    setDetecting(true);
+    try {
+      const list = ((await ListDenkoviDevices()) ?? []) as string[];
+      setDenkoviSerials(list);
+      // Auto-fill when there's exactly one and nothing chosen yet.
+      if (list.length >= 1 && !device.host.trim()) onChange({ ...device, host: list[0] });
+    } catch { setDenkoviSerials([]); }
+    finally { setDetecting(false); }
+  };
+  useEffect(() => { if (isDenkovi) void detectDenkovi(); /* eslint-disable-next-line */ }, [isDenkovi]);
   return (
     <div ref={ref} className="mt-4 max-w-4xl rounded-xl border border-primary/40 bg-card p-4 space-y-3">
       <div className="text-sm font-semibold">{device.id ? t('station.editDevice') : t('station.addDevice')}</div>
@@ -461,6 +477,7 @@ 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>
             </SelectContent>
           </Select>
         </div>
@@ -469,6 +486,24 @@ 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 ? (
+        <div className="space-y-1 max-w-md">
+          <Label>{t('station.ftdiSerial')}</Label>
+          <div className="flex items-center gap-2">
+            <Input className="font-mono flex-1" value={device.host} placeholder="DAE0006K"
+              list="denkovi-serials"
+              onChange={(e) => onChange({ ...device, host: e.target.value })} />
+            <datalist id="denkovi-serials">
+              {denkoviSerials.map((s) => <option key={s} value={s} />)}
+            </datalist>
+            <Button size="sm" variant="outline" onClick={detectDenkovi} disabled={detecting}>
+              {detecting ? <Loader2 className="size-3.5 mr-1 animate-spin" /> : <RefreshCw className="size-3.5 mr-1" />}
+              {t('station.detect')}
+            </Button>
+          </div>
+          <p className="text-[10px] text-muted-foreground">{t('station.ftdiHint')}</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')}>
           <Label>{t('station.host')}</Label>
@@ -487,6 +522,7 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
           </>
         )}
       </div>
+      )}
       <div className="space-y-1">
         <Label>{t('station.labels')}</Label>
         <div className="grid grid-cols-4 gap-2">

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.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.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.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.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/main/App.d.ts

@@ -546,6 +546,8 @@ export function ListContests():Promise<Array<contest.Def>>;
 
 export function ListCountries():Promise<Array<string>>;
 
+export function ListDenkoviDevices():Promise<Array<string>>;
+
 export function ListOperatingTree():Promise<Array<operating.Station>>;
 
 export function ListProfiles():Promise<Array<profile.Profile>>;

frontend/wailsjs/go/main/App.js

@@ -1050,6 +1050,10 @@ export function ListCountries() {
   return window['go']['main']['App']['ListCountries']();
 }
 
+export function ListDenkoviDevices() {
+  return window['go']['main']['App']['ListDenkoviDevices']();
+}
+
 export function ListOperatingTree() {
   return window['go']['main']['App']['ListOperatingTree']();
 }

internal/relaydev/denkovi_other.go

@@ -0,0 +1,29 @@
+//go:build !windows
+
+// The Denkovi USB board is driven through FTDI's D2XX bit-bang API (ftd2xx.dll),
+// which OpsLog only wires up on Windows. This stub keeps the package building on
+// other platforms; every call reports the board is unavailable.
+package relaydev
+
+import (
+	"context"
+	"fmt"
+)
+
+type denkoviStub struct{}
+
+// NewDenkovi returns a stub on non-Windows builds.
+func NewDenkovi(serial string) Device { return denkoviStub{} }
+
+func (denkoviStub) Count() int { return 8 }
+func (denkoviStub) Status(context.Context) ([]bool, error) {
+	return nil, fmt.Errorf("Denkovi USB relay board is only supported on Windows")
+}
+func (denkoviStub) Set(context.Context, int, bool) error {
+	return fmt.Errorf("Denkovi USB relay board is only supported on Windows")
+}
+
+// ListDenkovi has no devices to report off Windows.
+func ListDenkovi() ([]string, error) {
+	return nil, fmt.Errorf("Denkovi USB relay board is only supported on Windows")
+}

internal/relaydev/denkovi_windows.go

@@ -0,0 +1,181 @@
+//go:build windows
+
+// Denkovi USB 8-channel relay board (FT245RL). Despite enumerating as a virtual
+// COM port, this board is NOT driven by serial/ASCII: the FT245's 8 data lines
+// each drive a relay, controlled through FTDI's D2XX "bit-bang" mode. One byte
+// written = the 8 relays at once (bit 0 = relay 1). We load ftd2xx.dll at runtime
+// (no CGO) and call the D2XX API directly, exactly as the vendor's tool does
+// (which addresses the board by its FTDI serial, e.g. "DAE0006K").
+package relaydev
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"sync"
+	"syscall"
+	"unsafe"
+)
+
+var (
+	ftdll             = syscall.NewLazyDLL("ftd2xx.dll")
+	procOpenEx        = ftdll.NewProc("FT_OpenEx")
+	procClose         = ftdll.NewProc("FT_Close")
+	procSetBitMode    = ftdll.NewProc("FT_SetBitMode")
+	procSetBaudRate   = ftdll.NewProc("FT_SetBaudRate")
+	procWrite         = ftdll.NewProc("FT_Write")
+	procPurge         = ftdll.NewProc("FT_Purge")
+	procCreateInfo    = ftdll.NewProc("FT_CreateDeviceInfoList")
+	procGetInfoDetail = ftdll.NewProc("FT_GetDeviceInfoDetail")
+)
+
+const (
+	ftOpenBySerial  = 1    // FT_OPEN_BY_SERIAL_NUMBER
+	ftBitModeSyncBB = 0x04 // FT_BITMODE_SYNC_BITBANG (the mode Denkovi documents)
+	ftPurgeRX       = 1    // FT_PURGE_RX
+)
+
+func ftOK(r uintptr) bool { return r == 0 } // FT_OK == 0
+
+type denkovi struct {
+	serial string
+	count  int
+	mu     sync.Mutex
+	shadow byte    // last output byte (bit n = relay n+1); authoritative state
+	h      uintptr // FT handle
+	opened bool
+}
+
+// NewDenkovi builds a driver for a Denkovi USB 8-relay board identified by its
+// FTDI serial number (shown by the vendor tool / FT_PROG, e.g. "DAE0006K").
+func NewDenkovi(serial string) Device {
+	return &denkovi{serial: strings.TrimSpace(serial), count: 8}
+}
+
+func (d *denkovi) Count() int { return d.count }
+
+// ensureOpen opens the board and puts it in synchronous bit-bang mode with all 8
+// lines as outputs. Idempotent.
+func (d *denkovi) ensureOpen() error {
+	if d.opened {
+		return nil
+	}
+	if err := ftdll.Load(); err != nil {
+		return fmt.Errorf("FTDI D2XX driver (ftd2xx.dll) not found — install the FTDI D2XX driver / Denkovi software: %w", err)
+	}
+	if d.serial == "" {
+		return fmt.Errorf("no FTDI serial number set for the Denkovi board")
+	}
+	ser, err := syscall.BytePtrFromString(d.serial)
+	if err != nil {
+		return err
+	}
+	var h uintptr
+	if r, _, _ := procOpenEx.Call(uintptr(unsafe.Pointer(ser)), ftOpenBySerial, uintptr(unsafe.Pointer(&h))); !ftOK(r) {
+		return fmt.Errorf("cannot open Denkovi board %q (FT_OpenEx status %d) — is it connected and not in use by another app?", d.serial, r)
+	}
+	// All 8 lines output, synchronous bit-bang.
+	if r, _, _ := procSetBitMode.Call(h, 0xFF, ftBitModeSyncBB); !ftOK(r) {
+		procClose.Call(h)
+		return fmt.Errorf("FT_SetBitMode failed (status %d)", r)
+	}
+	procSetBaudRate.Call(h, 9600) // bit-bang pin-update clock; relays don't need speed
+	d.h = h
+	d.opened = true
+	// Make the hardware match our shadow (starts all-off on first open).
+	return d.writeLocked()
+}
+
+// writeLocked pushes the shadow byte to the relays. Caller holds d.mu.
+func (d *denkovi) writeLocked() error {
+	var written uint32
+	b := d.shadow
+	if r, _, _ := procWrite.Call(d.h, uintptr(unsafe.Pointer(&b)), 1, uintptr(unsafe.Pointer(&written))); !ftOK(r) {
+		return fmt.Errorf("FT_Write failed (status %d)", r)
+	}
+	// Synchronous bit-bang echoes each written byte into the RX buffer; drop it so
+	// it doesn't fill over the life of the connection.
+	procPurge.Call(d.h, ftPurgeRX)
+	return nil
+}
+
+func (d *denkovi) Set(ctx context.Context, relay int, on bool) error {
+	if relay < 1 || relay > d.count {
+		return fmt.Errorf("relay %d out of range 1..%d", relay, d.count)
+	}
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	if err := d.ensureOpen(); err != nil {
+		return err
+	}
+	bit := byte(1) << uint(relay-1) // relay 1 → bit 0
+	if on {
+		d.shadow |= bit
+	} else {
+		d.shadow &^= bit
+	}
+	return d.writeLocked()
+}
+
+func (d *denkovi) Status(ctx context.Context) ([]bool, error) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	if err := d.ensureOpen(); err != nil {
+		return nil, err
+	}
+	out := make([]bool, d.count)
+	for i := 0; i < d.count; i++ {
+		out[i] = d.shadow&(byte(1)<<uint(i)) != 0
+	}
+	return out, nil
+}
+
+// ListDenkovi returns the FTDI serial numbers of connected devices, for the
+// settings UI to pick from. Requires ftd2xx.dll.
+func ListDenkovi() ([]string, error) {
+	if err := ftdll.Load(); err != nil {
+		return nil, fmt.Errorf("FTDI D2XX driver (ftd2xx.dll) not found — install the FTDI D2XX driver / Denkovi software")
+	}
+	var n uint32
+	if r, _, _ := procCreateInfo.Call(uintptr(unsafe.Pointer(&n))); !ftOK(r) {
+		return nil, fmt.Errorf("FT_CreateDeviceInfoList failed (status %d)", r)
+	}
+	var out []string
+	for i := uint32(0); i < n; i++ {
+		var flags, typ, id, loc uint32
+		serial := make([]byte, 16)
+		desc := make([]byte, 64)
+		var h uintptr
+		r, _, _ := procGetInfoDetail.Call(
+			uintptr(i),
+			uintptr(unsafe.Pointer(&flags)), uintptr(unsafe.Pointer(&typ)),
+			uintptr(unsafe.Pointer(&id)), uintptr(unsafe.Pointer(&loc)),
+			uintptr(unsafe.Pointer(&serial[0])), uintptr(unsafe.Pointer(&desc[0])),
+			uintptr(unsafe.Pointer(&h)),
+		)
+		if !ftOK(r) {
+			continue
+		}
+		if s := cstr(serial); s != "" {
+			out = append(out, s)
+		}
+	}
+	return out, nil
+}
+
+// cstr trims a C string (up to the first NUL) from a fixed buffer.
+func cstr(b []byte) string {
+	if i := indexByte(b, 0); i >= 0 {
+		b = b[:i]
+	}
+	return strings.TrimSpace(string(b))
+}
+
+func indexByte(b []byte, c byte) int {
+	for i := range b {
+		if b[i] == c {
+			return i
+		}
+	}
+	return -1
+}