Frequently asked questions

Windows: serial ports and USB-serial adapters, Bluetooth LE, USB HID devices and TCP. Android: USB-serial adapters over USB-OTG, Bluetooth LE and TCP. The built-in Demo device answers like a real board, so you can try everything without hardware.

Open Devices and connect to Demo. It echoes what you send and answers a few commands. On the Scenarios screen, Load the demo scenario and press Run to see a complete pass/fail test.

Not in this version. LinkJig talks to Bluetooth LE modules (HM-10, ESP32, nRF and similar). Classic Bluetooth serial is planned.

Not yet. LinkJig runs on Windows and Android.

Many ESP32 and Arduino boards reset or enter the bootloader when the DTR or RTS line changes. LinkJig keeps both off by default and sets them the moment the port opens, so connecting does not pulse them. If your board needs them on, turn on DTR on after connecting or RTS on after connecting in the serial settings.

Another program has the port open — usually a serial monitor, an IDE or a second LinkJig window. Close it and press Retry. The message shows the real Windows error, so "access denied" means busy, not a broken cable.

The baud rate does not match the device. LinkJig notices unreadable data and offers Change baud. If you don't know the rate, use Find baud rate in the serial settings: it tries the common rates (115200 first), sends a command you choose (for example AT) or just listens, and stops at the first rate that gives a readable answer. Data bits, parity and stop bits must also match; most devices use 8N1, the default.

Check, in this order:

• Line ending. Most devices act only after the end of a line. The default is CR LF (\r\n); some devices want only CR or only LF.
• Wiring. TX goes to RX, RX to TX, and the grounds are connected.
• Baud rate and the other line settings.
• The send bar shows the exact bytes before you send, so you can compare them with the device's manual.

Use a USB-OTG adapter or cable, then plug the adapter in. Android asks whether LinkJig may use the device — allow it. Some phones need OTG switched on in their settings. Adapters with CP210x, CH34x, FTDI and PL2303 chips, and CDC-ACM boards, are supported.

Some phones cut USB-OTG power at low battery. LinkJig warns you when this may happen. Charge the phone or use a powered OTG hub.

Check that Bluetooth is on and that LinkJig has the "Nearby devices" permission (Android 12 and newer) or Location (Android 11 and older). LinkJig says plainly when a permission is missing or Bluetooth is off; "No devices found" means the scan worked and nothing answered. Many BLE modules stop advertising while something else is connected to them.

On Android 11 and older, the system shows nearby Bluetooth devices only to apps with Location permission. LinkJig never reads or stores where you are.

Nordic UART (NUS), TI CC254x / HM-10 (FFE0) and Microchip transparent UART are detected automatically. For other modules LinkJig picks a service with a writable and a notifying characteristic. If it picks the wrong one, open the GATT explorer from the terminal menu, choose the TX and RX characteristics and press Use for terminal.

Choose Network, enter the host name or IP address and the port, and connect. LinkJig connects as a TCP client — for example to an ESP32 or a serial-to-Wi-Fi bridge. Devices that announce themselves with mDNS (such as esp32.local) appear under On this network after you press Find.

In Network, tap Scan in the Wi-Fi section and tap the module's network. Enter its password once; with Remember password on, a tap is enough next time. After joining, LinkJig fills in the module's address (usually 192.168.4.1): press Connect. The saved connection remembers the Wi-Fi, so later one tap joins the network and connects. On Android, the first scan asks for the Location permission: Android lists Wi-Fi networks only to apps that have it. LinkJig never reads where you are.

On Android 10 and newer, no: only LinkJig uses the module's network and the rest of the phone stays online. On Windows and Android 9 the whole device switches to the module's network until you tap Leave (or Back to … on Windows). Windows never joins a module's network by itself later.

On Windows, yes. Under Saved connections, open the connection's menu and choose Create desktop shortcut. Opening it starts LinkJig, joins the saved Wi-Fi if the connection has one, and connects. The shortcut never contains a password.

Only on your device: on Android encrypted with a key in the Android Keystore and left out of backups; on Windows in the system's Wi-Fi profile. To remove one, open the network's menu in the Wi-Fi list and choose Forget password.

Not in this version.

Switch the input format in the send bar to HEX and type bytes such as 01 03 00 00 00 0A. DEC and BIN work the same way. In text (ASCII) mode you can write escapes: \r, \n, \t and \xNN for any byte.

Control keys are single bytes: Ctrl+C is \x03, Ctrl+D is \x04, Ctrl+Z is \x1A (Esc is \e). In text (ASCII) mode type \x03, or switch to HEX and type 03; set the line ending to No EOL if the device expects the byte alone. Save it as a macro to send it with one tap. On Windows, Ctrl+C in the terminal copies the selection; it does not send anything.

Yes. Pick a checksum in the send bar (SUM8, XOR8, CRC-8, CRC-16/MODBUS, CRC-16/CCITT-FALSE or CRC-32); it is added after your data and before the line ending, and the preview shows the result. The Checksum calculator in Settings → Tools works on any bytes without sending.

LinkJig groups received bytes into packets. By default a packet ends when no data arrives for 20 ms (Time gap). In Settings → Packet framing you can split at delimiter bytes (for example 0D 0A) instead, or show every read as it arrives (Raw).

Change the View in the terminal: ASCII, HEX, DEC, BIN or Dump (offset + hex + text). On Windows, Ctrl+E switches between them and Ctrl+T switches timestamps. The view changes only the display; the bytes are kept as received.

Yes. The timer button in the send bar sends the current input at a fixed interval until you stop it. The paperclip button sends a file, either as binary chunks or line by line, with a delay between parts.

RX is data received from the device, TX is data you sent. The thin rails at the terminal edges mark where RX (left) and TX (right) happened; click a mark to jump there.

A saved command on a button. Tap it in the macro bar under the terminal, or press F1–F12 on Windows. Shift+F1–F12 edits the macro.

A rule that watches every received packet for a text, hex (with ?? wildcards) or regex pattern. When it matches, LinkJig can send a reply, mark the line in the log, beep, save a snapshot or stop a running scenario. Use triggers to answer a device automatically or to simulate one.

A repeatable test. Each step sends a message, waits for the expected reply within a timeout and marks the step PASS or FAIL. You choose what happens on a failure (continue, retry or stop) and how many loops to run. Save the result as a text report or CSV table.

Yes. Build them on the desktop, share them as a project pack and import it on the phone. The phone runs them and shows each step's result.

A profile stores connection and send settings (and optionally macros) for one device. A project pack bundles profiles, macros, triggers, scenarios and an optional sample log into one .ljpack file to share with a colleague or move to your phone.

No. Importing only adds scenarios, macros, triggers and profiles. Nothing is sent until you press Run or Send.

Automatic session logging is off by default; turn on Save every session to disk in Settings → Terminal. On Windows the logs go to Documents\LinkJig\logs (trigger snapshots in snapshots). On Android they stay inside the app; on the Logs screen, Save a copy… lets you send a log or store it elsewhere. You can also save the current terminal from its menu at any time (Ctrl+Shift+S on Windows).

No. With Restore last session on (the default), the last 2,000 lines come back on the next start. LinkJig never reconnects by itself; it asks first.

On Android, yes, while a link is active: LinkJig shows an "Active connection" notification so the system keeps it running. If you turn notifications off, the link still runs but the notification is hidden. Some phone makers stop background apps aggressively; if links drop, allow LinkJig to run without battery restrictions.

The tool is free and never shows ads: not in the terminal, devices, scenarios, macros, triggers, logs, library, settings or help. On Android there is an optional mini game, Start Bit (Settings → Help); ads appear only inside it. You never need to open it. The desktop app has no game and no ads.

Pro is free. On Android, either win level 15 in Start Bit or watch 10 short ads (at most 5 a day), whichever comes first. Pro then stays unlocked for good; the mini game keeps its ads, the tool never shows any. Before that, scenarios and triggers can be tried in full on the Demo device.

Unlock Pro in the Android app, then Settings → Pro → Unlock the desktop app. Each code takes 2 short ads and is valid for 48 hours; enter it on the computer in Settings → Pro → Enter code. The computer goes online once, only to check the time.

No, as long as Android backup is on for your Google account. Pro, themes and game progress are kept in one encrypted file, and that file is the only thing LinkJig puts in the backup.

Each Start Bit chapter you finish unlocks one theme; you can also unlock a theme with 3 short ads. Themes change colors only. The desktop app has the standard light and dark looks.

No. There is no account, no analytics and no server. Everything you type, receive and save stays on your device. The optional Start Bit mini game on Android gets its ads from Google AdMob, which never sees your terminal data. See the privacy policy in Settings → About.

Settings → Appearance → Language. System follows your device's language.

Settings → Help → Copy diagnostic report, then paste it into your message to linkjig.app@gmail.com. The report contains app, system and link details — never terminal data, serial numbers or addresses.