Bit banging through a USB parallel port adapter

bit-banging-through-a-usb-parallel-port-adapter

If you’ve ever looked into low-level parallel port access you may have learned that it only works with actual parallel port hardware, and not with USB parallel port adapters. But here’s a solution that will change your thinking. It borrows from the way printers communicate to allow USB to parallel port bit banging without a microcontroller.

Sure, adding a microcontroller would make this dead simple. All you need to do is program the chip to emulate the printer’s end of the communications scheme. But that’s not the approach taken here. Instead the USB to RS232 (serial) converter also pictured above is used as a reset signal. The strobe pin on the parallel port drives an inverter which triggers a thyristor connected to the busy pin. Thyristors are bistable switches so this solution alone will never clear the busy pin. That’s where the serial connection comes into play. By alternating the data transmitted from the computer between the bit-bang values sent to LP0 and 0xF0 sent to the serial connector the eight parallel data bits become fully¬†addressable. See the project in action in the clip after the break.

A CD Changer Made of Wood

Although this is by no means a new hack – it was made circe 2002 – this wooden CD changer is an interesting piece of machinery. The whole thing is a simple pick-and-place device. The gripper is brilliant in it’s simplicity, using only a rubber band, wood, and a solenoid. It grips the CD by the middle hole, picks it up, and the assembly then travels to the CD tray or the stack. Everything works with DC motors and string, and several micro-switches make sure everything is picked up and dropped in the correct position.

Although we may think this is a pretty cool device, [Matthias] is quite humble about his machine’s abilities. In his estimation, although one could probably duplicate 12 CDs with relative ease, if you really wanted to duplicate a large number, it’d be best to buy one. Maybe he works in manufacturing.

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Beginner concepts: LPT instead of uC

We see it all the time, a post based on an Arduino board with multiple comments calling it overkill. How exactly should you control your homemade peripherals if you’re not using a microcontroller (uC)? [JKAbrams] and [Tim Gremalm] answered that question with this printer port (LPT) adapter. They wanted an indicator light when someone in an IRC room was talking to them. By connecting a blue rotating light through a relay to the output of this fob they’ve done just that, but there’s room for much more.

The adapter uses a Darlington transistor array IC to protect the computer. A resistor between the LPT and the base pin on the chip ensures that current flow will be well within the safe levels for the computer. The Darlington transistor amplifies the output using an external power supply in order to drive heavier loads.

If you want a deeper understanding of the printer port check out this tutorial. LPT ports are becoming less common and that’s why so many projects are migrating over to USB (plus there’s no need for external power with most USB connected projects) but if you’ve got one, it’s probably not being used for anything else.

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