LPT relay-board circuits
Before we had microcontrollers like the Arduino, to control electronics from a PC through USB, I used to build some LPT-based circuits. Today it is easier to just use an Arduino for robotic projects and small circuits. Still it was fun to explore the LPT port, and programming for LPT in Delphi...
The LPT port (DB25 LPT-connector)
The LPT port runs up to 5 volt DC. There is 3 bytes (each of 8 bits) to control the port.
Single LPT output-pin
Each output had a transistor gate (used for converting 5 volt of the pin to ground for external supply).
An output pin was connected to a BC547 NPN transistor, through a 1N4448 diode (75V/0,1A) (to protect the port). The BC547 transistor requires only <1 volt (through a ~3,3k resistor), to open for ground on the collector pin. Also a ~10k resistor was used for transistor pull-down. "Optional gate 2" had a ~680 ohm resistor for the BD136 PNP transistor (Converting ground to external +12 volt DC.)
The LPT board
A >1000uF capacitor and a rectifier diode was used as power supply for the circuit. Also a transistor gate for each 12 outputs, and further 5 transistors for each feedback input. All outputs connected to LEDs, and also to pins on the ATA/IDE-connector.
In this project the "optional gate 2" for each output was placed on seperate board as an extension.
Used to drive relays or other stuff that uses more power. A small power supply (the capacitor). 10 x BD135 NPN transistor with 1 K-Ohm resistors
Relay expansion board
First test, 2005
LPT Relay board 1.0, 2005
The first relay board designed as a test on cheap print (with lanes)
Arduino leds, relays and transistors 5x5 pcs
Using and Arduino Mega board to control 25 car relays and LED's in different patterns. An Arduino digital output pin first goes to a bc547 npn transistor, and the bc547 signal then goes to a bd136 pnp transistor (bd135 npn sibling), in order to switch the relays from an Arduino. The Arduino was programmed with several different patterns and was switched from an E-Fly remote controller.
Related pages of LPT relay-board circuits
|Resistor color values|
|4WD Robot Vehicle 24v|