Q1-Q8 D1-D16 L1-L8 |
BC547B 1N4148 LED |
| LPTLEDS project |
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[schematic] [lptleds.zip] [electro page] [R's Homepage]
LPTLEDS is a device with eight leds that you can turn on/off by sending a databyte to your LPT/parallel/centronix port on your computer.
In this schematic you can see the circuit i've developed for the LPT leds.
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You might think that it's a lot of components. Sure, you're right. But this approach enables varying supply voltages from 3 to 30 Volts. Maybe the 16 diodes, 8 transistors and 8 base resistors could be replaced by one "driver/buffer/receiver/latch" IC. Only thing is than i couldn't find an IC that works on a varying supply voltage range and still accept the standard TTL voltage levels from the LPT port.
In fact, the schematic is 8 times a small schematic, 1 for each bit of the byte. A BC547B transistor, with a 33K Ohm resistor connected between the base and a 'bit' of the LPT port. The current trough the LED is determined by the 56 Ohm resistor between emitter and ground, and 2 1N4148 diodes between base and ground. This current is theoretically:
(2 x Udiod - Ube) / R
(2 x 0.7 - 0.7) / 56 = 12.5 mA
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Maybe you have never used your LPT port for anything else than printing, and you don't know how to address the LPT port, talk to it using a programming language.
Information about addresses, registers, and pin-out of the LPT port can be found in my LPTPORT document.
If electronics is one of your hobby's, and programming isn't, you can use my LPTLEDS program. It enables you to load and run various 'RUNNING LIGHTS' patterns. You can easily create your own pattern in a text editor (DOS editor, notepad).
This archive contains:
lptleds.txt
lptschem.gif
lptport.txt
lptleds.exe, kngrdr01.lpf, kngrdr02.lpf, test.lpf
DOWNLOAD LPTLEDS.ZIP ARCHIVE (47 KB)
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