FAQ
TL;DR: For desktop-controlled IR locks, skip legacy LPT and use USB‑to‑serial; Steve shared 5 example adapters and noted, “what you want is a USB to TTL.” [Elektroda, Steve Lawson, post #21665948]
Why it matters: This approach works on modern PCs, simplifies coding, and avoids brittle parallel‑port drivers—perfect for beginners building reliable locks.
Quick Facts
- Windows NT/XP often blocks direct I/O to LPT without a helper driver or toolkit. [Elektroda, Mark Harrington, post #21665942]
- XP tweak: Disable LPT warm polling via DisableWarmPoll=1 at the Parport\Parameters key (advanced users only). [Elektroda, Eugene Lisovy, post #21665964]
- Direct port access toolkits exist for NT-like Windows and DOS tasks. [Elektroda, Eugene Lisovy, post #21665961]
- Low-cost DIY USB‑to‑LPT bridge: AVR-based USB2LPT project with schematics. [Elektroda, Eugene Lisovy, post #21665966]
- Beginner GUIs: Visual Basic, Delphi, and Tcl/Tk can drive a virtual COM port. [Elektroda, Steve Lawson, post #21665958]
How do I control a PC port for an infrared lock in 2025?
Use a USB‑to‑serial (USB‑to‑TTL/RS‑232) adapter and drive a microcontroller (e.g., PIC/AVR) that switches your IR transmitter/relay. This avoids fragile LPT access on modern OSes and gives you a stable virtual COM port for your app. Steve’s post lists multiple adapter options. [Elektroda, Steve Lawson, post #21665948]
Should I avoid the parallel (LPT) port for new builds?
Yes. LPT is phased out on new PCs and driver access is inconsistent on NT/XP and later. Engineers in the thread moved to serial or USB front ends because they "always work" across systems. That reliability matters for locks and safety. [Elektroda, Mark Harrington, post #21665942]
What exactly is a USB‑to‑TTL/USB‑to‑RS232 adapter?
It converts USB from your PC into a UART signal (TTL level or RS‑232 level) that microcontrollers understand. Common chipsets include FTDI; vendors like SparkFun, Adafruit, and Parallax sell ready modules. Your PC sees a COM port you can open from most languages. [Elektroda, Steve Lawson, post #21665948]
Quick 3‑step: how do I build a simple USB/serial front end for the lock?
- Hardware: Pair an FTDI module or a MAX232 RS‑232 level shifter with a small MCU to drive your relay/IR LED.
- Firmware: Parse simple bytes/ASCII over UART to toggle lock states.
- PC app: Send commands from Java or C# over the virtual COM port. [Elektroda, Mark Harrington, post #21665956]
How can I access the LPT port on Windows XP/NT if I insist on using it?
Use a port‑access toolkit/driver designed for NT‑like systems to gain user‑mode I/O to LPT registers. This enables experiments or legacy hardware under controlled conditions, though it’s more brittle than USB‑serial. [Elektroda, Eugene Lisovy, post #21665961]
Is editing the Windows registry safe for LPT tweaks?
Treat it as risky. Back up the registry first. If something breaks, boot Safe Mode and restore. A single typo can derail your system. As Steve cautioned, "better safe than sorry." [Elektroda, Steve Lawson, post #21665965]
How do I disable Windows XP’s LPT polling and why would I?
DisableWarmPoll=1 under the Parport\Parameters key stops periodic LPT polling that can interfere with direct port experiments. This is an advanced change; document and back up before editing. [Elektroda, Eugene Lisovy, post #21665964]
Can a beginner build the GUI to lock/unlock?
Yes. Options include Visual Basic, Delphi, or Tcl/Tk. Each can open the adapter’s COM port and bind buttons to send bytes. Tcl/Tk is cross‑platform and approachable; VB offers a very friendly designer for quick results. [Elektroda, Steve Lawson, post #21665958]
What languages and tools did the thread suggest for the PC side?
Java, C#, VB, Delphi, and Tcl/Tk were suggested. Mark noted JDK7 was then current and highlighted cross‑platform benefits. Choose what you know; serial libraries exist for all. [Elektroda, Mark Harrington, post #21665956]
What’s FTDI, MAX232, LPT, and TTL in simple terms?
FTDI: USB‑UART bridge chips/modules. MAX232: converts TTL UART to RS‑232 levels. LPT: legacy 25‑pin parallel printer port. TTL: 5V/3.3V logic UART signal for MCUs. These terms appear across the suggested hardware paths. [Elektroda, Steve Lawson, post #21665948]
Is there a low‑cost DIY bridge if I must keep LPT hardware?
Yes. An AVR‑based USB2LPT project emulates a printer port over USB, useful for legacy devices when native LPT is unavailable. It includes schematics and firmware. [Elektroda, Eugene Lisovy, post #21665966]
Any beginner‑friendly learning resources or communities?
SparkFun tutorials and support forums are solid starting points. Follow a guided USB‑to‑serial example, then adapt it to send your lock commands. Ask questions as you hit roadblocks. [Elektroda, Steve Lawson, post #21665952]
Can I configure or test ports with HyperTerminal?
You can test serial communications with HyperTerminal by opening the virtual COM port and sending bytes to your MCU. It does not configure LPT, but it’s handy for serial debugging. [Elektroda, Aniruddh Mali, post #21665957]
What pitfalls should I expect on Windows XP and drivers?
Expect driver hurdles, 32‑bit vs 64‑bit confusion, and tools that work only in DOS/Win9x. Many gave up on LPT under XP and pivoted to serial/USB. Plan for that fallback early. [Elektroda, Mark Harrington, post #21665972]
Where can I read a primer on parallel ports?
Start with the tutorial linked in the thread. It explains LPT basics, signals, and interfacing concepts useful for understanding legacy control paths. [Elektroda, Eugene Lisovy, post #21665939]
Is Tcl/Tk still free for hobby use?
Yes. ActiveTcl offers a free Community edition with forum support, suitable for learning and small tools that talk to COM ports. [Elektroda, Steve Lawson, post #21665960]
