Why add 9 LEDs when every cheap USB-RS232 adapter only ships with TX and RX lights? That is the most common question we receive about the DeStatiX A9.

The limitation of conventional 2‑LED USB-RS232 adapters

Most USB to RS232 converters only include two status LEDs: TXD and RXD. These two lights can tell you one thing: is data moving across the serial line.

But RS232 is not just data bytes. The DB9 interface defines a full set of hardware handshake control signals: DTR, DSR, RTS, CTS, DCD, RI. These handshakes are critical for industrial controllers, CNC equipment, vintage computers and legacy serial peripherals.

Here is the core problem: Data can look silent or broken, even when TX/RX packets are working perfectly, because handshake lines are wrong.

With a standard 2-LED adapter, you cannot visually check these control signals. You must grab a multimeter, clip probes to DB9 pins one by one, measure DC voltage, and interpret the state manually. For field service, lab debugging or retro hardware repair, this is slow and error-prone. Many intermittent handshake bugs are hard to catch with spot meter readings.

What are the 9 LEDs on DeStatiX A9?

The DeStatiX A9 has nine signal indicator LEDs mapped to: GND, DTR, TxD, RxD, DCD, RI, CTS, RTS, DSR. There is no dedicated separate power LED on this adapter.

  • The GND LED is tied directly to ground. It will never illuminate; it is included as one of the nine physical signal test points, not a power indicator.
  • Built around an FTDI chipset: during USB enumeration and driver load after plugging in the USB cable, the DTR and RTS LEDs will briefly flash once. This is native behaviour of the FTDI Windows VCP driver on startup. It is not triggered by serial data transmission, and it is completely unrelated to our Python bit-bang test script.
  • The remaining signals (TxD, RxD, DSR, DCD, RI, CTS) do not produce this predictable flash during USB enumeration.

These LEDs give you instant visual state of all DB9 signals in real time. No tools required. Here are the practical failure scenarios this reveals:

  • A device ignores incoming data because CTS is not asserted, while TX/RX lines are electrically fine.
  • Serial connection fails because DTR/DSR handshake logic mismatches between host and peripheral.
  • DCD carrier detect signal missing on modem-style legacy equipment.
  • RI ring indicator triggering unexpected state changes on old telecommunication hardware.
  • Broken wiring inside DB9 cable: one handshake pin open or shorted, even if TX/RX still works.
  • Observe transient DTR/RTS events on port open, which are invisible on standard TX/RX-only adapters.

For hobbyists working on retrocomputing, technicians servicing factory PLCs, CNC machines, and lab engineers: handshake signals are not optional. They are often the root cause of serial communication failures that TX/RX-only adapters hide completely.

Are 9 LEDs overkill? It depends on your use case.

If you only send simple ASCII strings with no hardware handshaking, then yes: two LEDs are enough. You will never need to watch DCD or RI.

But if your work involves legacy RS232 hardware that relies on full DB9 handshaking, the 9 LED layout is not overkill — it is a deliberate diagnostic tool built into the adapter.

DeStatiX A9 is not designed to replace cheap basic USB serial adapters. It is built for diagnostic work. The goal is to turn invisible RS232 handshake states into visible lights.

Why we created the LED test script

Since the core value of this product is the full 9 LED visual feedback system, we need a simple way for users to verify that every LED channel works correctly after unboxing. A visual diagnostic tool is useless if one LED is dead and you cannot confirm it quickly.

We built a Python bit-bang test script using FTDI D2XX driver. The script cycles sequentially through all 8 active signal LEDs, lighting each one in turn. The user can watch the sequence and confirm every signal LED illuminates as expected. The GND LED remains permanently off.

This test is a quick QA validation: confirm that FTDI bitbang output, PCB traces and each LED circuit are functional before you start serial troubleshooting work.

Important note: This script uses FTDI D2XX native driver, NOT WinUSB. If Zadig was used to bind WinUSB to this FTDI interface, D2XX cannot open the device and the script fails. Restore official FTDI FTDIBUS / D2XX driver first.

Prerequisites

  1. Windows PC (Win10 / Win11)
  2. Official FTDI D2XX driver installed (avoid Zadig WinUSB for this interface)
  3. Python 3
  4. Install ftd2xx package: pip install ftd2xx
  5. Plug in DeStatiX A9

DeStatiX A9 LED Tester Source Code

Download the script

Save the file rather than copying it out of the page — in Python the indentation is syntax, and a lost space stops it running.

.py · 1 KB 
#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
DeStatiX A9 LED Tester - dynattenik@
Simple test for the 9 LED USB-RS232 adapter (8 signal LEDs + 1 power LED):
lights one LED at a time, in order, forever, until Ctrl+C.
    python DeStatiX_A9_LED_Tester.py          # 0.5 s per LED
    python DeStatiX_A9_LED_Tester.py 0.2      # 0.2 s per LED
Requires: pip install ftd2xx + FTDI official D2XX driver.
"""
import sys
import time
import ftd2xx
# bit0 TXD  bit1 RXD  bit2 RTS  bit3 CTS  bit4 DTR  bit5 DSR  bit6 DCD  bit7 RI
BIT = {'TXD': 0, 'RXD': 1, 'RTS': 2, 'CTS': 3,
       'DTR': 4, 'DSR': 5, 'DCD': 6, 'RI': 7}
ORDER = ['DTR', 'TXD', 'RXD', 'DCD', 'RI', 'CTS', 'RTS', 'DSR']  # lighting order
DELAY = 0.5                                                       # seconds per LED
def main():
    delay = float(sys.argv[1]) if len(sys.argv) > 1 else DELAY
    dev = ftd2xx.open(0)              # first D2XX device
    dev.setBaudRate(921600)
    dev.setBitMode(0xFF, 0x01)        # 0x01 = asynchronous bit-bang, all outputs
    print('dynattenik@  DeStatiX A9 LED tester  -  Ctrl+C to stop')
    print('order: %s' % ' -> '.join(ORDER))
    try:
        while True:
            for name in ORDER:
                value = 0xFF ^ (1 << BIT[name])   # pull one bit low = LED on
                dev.write(bytes([value]))
                print('\r  LED: %-4s  byte: 0x%02X  %s'
                      % (name, value, format(value, '08b')), end='', flush=True)
                time.sleep(delay)
    except KeyboardInterrupt:
        print('\nstopping ...')
    finally:
        dev.write(b'\xFF')            # all LEDs off
        dev.setBitMode(0x00, 0x00)    # leave bit-bang mode
        dev.close()
        print('all LEDs off, device closed.')
if __name__ == '__main__':
    main()

Run the test

Default 0.5 second per LED:

python DeStatiX_A9_LED_Tester.py

Faster sweep at 0.2 seconds:

python DeStatiX_A9_LED_Tester.py 0.2

Watch the DeStatiX A9 LEDs cycle through your defined sequence. The GND LED will stay off the whole time. If any of the other signal LED does not light up, you immediately identify a hardware fault. Press Ctrl+C to terminate; the script safely shuts down bitbang mode and turns all signal LEDs off.

Who benefits most from DeStatiX A9?

  • Field technicians troubleshooting industrial PLC and RS232 controlled CNC equipment
  • Retrocomputing enthusiasts repairing vintage serial peripherals and modems
  • Lab engineers validating DB9 serial cabling and handshake logic
  • Educators teaching RS232 hardware handshaking principles
  • Small production QA validation for serial hardware