KISS over USB Serial

Connect a serial KISS TNC directly to an Android tablet over USB.

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This interface type is available on Android only. Configure it from the graywolf app on your Android tablet. On macOS, Linux, and Windows, use KISS over Serial instead.

Overview

Some TNCs and radios speak KISS natively over a serial port. When you plug one of these devices into an Android tablet over USB, graywolf can use it as a full radio channel -- beacon into it, digipeat across it, and iGate from it -- without an audio modem or a network connection between graywolf and the device.

Common examples include the Kenwood TH-D75 (which appears as a USB serial device and speaks KISS when placed in packet mode), Mobilinkd TNCs, and USB-to-serial cables such as Digirig, CP210x-based cables, and CH34x-based cables connected to a radio with a serial KISS port.

Graywolf opens the USB serial connection, reads KISS frames as they arrive, and writes KISS frames when transmitting. The device handles all RF carrier sensing, timing, and actual transmission; graywolf is just the packet router on top.

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Putting the radio or TNC into KISS mode is the operator's responsibility. Graywolf opens the connection and begins speaking KISS immediately; it does not send any AT commands or mode-switching sequences. Consult your device's manual for the procedure to enter KISS mode before connecting it in graywolf.

Supported Devices

Graywolf recognizes USB serial devices based on their USB vendor and product identifiers. The device picker in the graywolf app lists every connected device that uses a supported USB serial chip, showing the product name alongside the vendor:product ID pair.

Supported chip families include:

If your device does not appear in the list, confirm it uses one of these chip families. Devices that present only as audio or HID interfaces (with no serial chip) will not appear.

Baud Rate

The baud rate you enter in graywolf must match the baud rate configured on the device. Common values:

A baud-rate mismatch produces garbage framing. If the KISS interface appears connected but no frames arrive (or arrive as decode errors), verify that both sides are set to the same rate.

Configuration

Step 1 -- Create a KISS-only channel

  1. Open Radio → Channels in the graywolf app.
  2. Tap + Add Channel.
  3. In the channel-type segmented control at the top of the form, choose KISS-TNC only. The audio device, modem type, and TX timing fields disappear -- a KISS-only channel is a logical routing lane, not a modulated radio channel.
  4. Name it to reflect the attached device (for example, TH-D75 or Mobilinkd). Give it a channel number that does not collide with your existing RF channels.
  5. Tap Save. The channel appears on the list with a KISS-TNC only badge. Its backing shows -- Unbound until you attach the USB serial KISS interface below.

Step 2 -- Plug in the device

Connect the serial KISS TNC to the tablet's USB port. Use an OTG (On-The-Go) adapter or hub if your tablet has a USB-C or Micro-USB port and the cable has a standard-A connector.

Step 3 -- Grant USB permission

Android requires explicit permission before any app can access a USB device. When graywolf first sees a newly plugged serial device, it requests permission from the operating system. Android shows a system dialog asking whether to allow graywolf to access the device. Tap OK. After you grant permission, the device appears in the picker.

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Permission is granted once per device per app install. If you unplug and replug the same device later, graywolf reconnects automatically without showing the dialog again. If you see the dialog again after a replug, it means the device was fully re-enumerated by Android with new identifiers (this can happen on some OTG hubs).

On the KISS TNC configuration form, tap Grant USB permission if the button appears. This sends the permission request and refreshes the device list. The button disappears once permission is granted.

Step 4 -- Create a USB Serial KISS interface

  1. Open Interfaces → KISS TNC (the page is titled KISS Interfaces).
  2. Tap + Add KISS.
  3. In the Type field, choose USB Serial.
  4. In the Device picker, select your device from the list. Each entry shows the product name and the USB vendor:product ID (for example, TH-D75 [35BF:0004] or Digirig Mobile [10C4:EA60]). If no devices appear, confirm the cable is plugged in and USB permission has been granted.
  5. Set Baud Rate to match the rate configured on the device (9600 is the most common starting point).
  6. In the Channel picker, select the KISS-only channel you just created.
  7. Set Mode to TNC. In TNC mode the interface is treated as a radio, not a software client. This also reveals the transmit opt-in checkbox.
  8. Check the box labeled Allow digipeater/beacon/iGate to transmit on this interface to allow graywolf's TX pipeline to send frames to the device. Without this checkbox the interface only receives.
  9. Tap Create. Graywolf opens the USB serial connection immediately. The row's status badge shows Connected if the device opened successfully. The channel's backing on the Channels page flips to ● Live.
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Make sure the device is already in KISS mode before saving the interface in graywolf. Graywolf does not issue any mode-switch commands; it assumes the connection is already speaking KISS when it opens it.

Reconnect Behavior

If the device is unplugged, graywolf detects the disconnect and marks the interface as reconnecting. When you plug the device back in, Android notifies graywolf and the connection is re-established automatically. You do not need to restart the app or reconfigure the interface. The channel returns to ● Live status once the connection is open.

Editing the device, baud rate, or mode on the KISS TNC page and tapping Save triggers a hot reload: graywolf closes the existing connection and re-opens it with the new settings.

USB Serial and PTT

A USB-to-serial cable such as a Digirig or a CP210x or CH34x cable can serve as either a PTT keying device or a serial KISS TNC, but not both at once. When you configure a cable as a USB Serial KISS interface, graywolf claims that USB device exclusively for KISS use and releases any PTT claim on it. If the same cable was previously used for PTT, that PTT configuration stops working until you reassign it to a different device.

To use one cable for PTT and a separate cable for KISS serial, plug in two cables and configure them independently. The device picker shows each cable by its product name and vendor:product ID.

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CDC-ACM devices such as the Kenwood TH-D75 and the AIOC present a single USB interface that carries both the serial data and the PTT signal inside the KISS stream. They are not affected by this limitation -- KISS takes full ownership of the device and PTT is handled by the TNC itself.

Troubleshooting

Device does not appear in the list

  1. Confirm the cable is fully seated in the tablet's USB port and the tablet's USB OTG adapter (if used) is working.
  2. Confirm the device uses a supported chip (CDC-ACM, CP210x, or CH34x). A USB audio-only or HID-only device will not appear.
  3. Tap Grant USB permission on the KISS interface form. The system permission dialog may be waiting behind another app.
  4. Unplug and replug the cable. If the device re-enumerates, Android delivers a fresh attach event and graywolf refreshes the list.

Interface connects but no frames arrive

  1. Confirm the device is actually in KISS mode. Most radios and TNCs default to a human-readable command mode and must be explicitly switched. Consult your device's manual.
  2. Verify the baud rate matches on both sides. A mismatch produces garbage bytes that the KISS framer discards.
  3. Confirm the device is transmitting. On a radio such as the TH-D75, the APRS channel must be active and a beacon must be due -- the port is silent between packets.
  4. Check the Logs page in the graywolf app for any serial framing or open errors.

My beacon on the channel does not transmit

Known-Working Devices

DeviceUSB IDBaud RateNotes
Kenwood TH-D75 35BF:0004 9600 Enable packet mode in the radio's menu and set the data speed to 9600 bps. The radio must be tuned to an APRS frequency.
Kenwood TH-D74 35BF:0003 9600 Similar to the TH-D75. Use the radio's APRS menu to confirm it is in packet / KISS mode.
Digirig Mobile 10C4:EA60 (CP210x) 9600 Connect Digirig to the radio's data port. Set the radio's packet port to 9600 baud and enable KISS mode.
Mobilinkd TNC4 varies by revision 38400 Configure via the Mobilinkd app before connecting to graywolf. KISS mode is selected in the app. Baud rate may vary by firmware version; confirm in the app.

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