GPIO for the PDM

Updated 1 month ago by Bryan Jones

SCOPE

This document applies to he 25-Seven PDM and specifically covers wiring and use of the GPIO Parallel Port connections.

GPIO

Eight parallel control inputs and eight parallel control outputs appear on the female DB-25 connector, with pinouts detailed below. Input and output functions are assigned through the GPIO menu. Please reference the full PDM Manual for information on use of the menus.

Inputs and outputs are opto-isolated for easy interface to other equipment. A +5v supply and ground are also brought out to the DB-25 for simple remote controls using pushbuttons and LED status readouts. If an output signal is a pulse, its opto-isolator will turn on for between 100ms and 1000ms (adjustable on the configuration screen). Factory default is 250ms.

The +5v supply can provide 200 mA, more than adequate for 8 LEDs and 8 logic inputs. Total draw should not exceed this value. This supply is protected by an internal, self-resetting thermal circuit breaker. If this breaker should trip, power off and allow several minutes for it to reset.

Basic remote control
  1. Use the connections shown on the left side of the schematic below. At the DB-25, jump pin 13 (input common) to pin 8 (+5v).
  2. Connect one side of an SPST NO pushbutton to pin 20 (ground); connect the other side to pin 25 (Input 1).
  3. Add up to 7 more pushbuttons as needed, connecting one side of all to pin 13 as common, and connecting their other sides to the individual inputs in the chart below.
Typical PDM remote input (left) and output (right) circuits. Use the jumpers shown in gray for simple pushbutton / LED remote. Or use just the opto-isolator connections without pins 8 and 20 for interface to other equipment. DB-25 pinouts shown in bold. * indicates individual DB-25 pins for separate GPIO inputs and outputs; see chart below.
Basic remote readout
  1. Use the connections shown on the right side of the schematic. At the DB-25, connect pin 7 (output common) to pin 20 (PDM ground).
  2. Connect a 4.7 kΩ 1/4 watt resistor between pin 8 (+5 V) and the anode or + lead of an LED; connect the cathode or – lead of the LED to pin 19 (output 1).
  3. Add up to 7 more resistor-and-LED combinations as needed, using pin 8 as the common voltage supply and connecting the LEDs cathodes to individual outputs in the chart below
Connecting to external logic or relay circuits:

PDM’s GPIO inputs and outputs are isolated from its power supply and ground, and can be connected to external logic circuits or the power supplies in remote equipment:

  • Inputs require at least 6 mA flowing from the input common (pin 13) and the individual input circuit pin.
  • Outputs can carry up to 25 mA, up to 30 V DC per channel, between the individual output circuit pin and output common (pin 7).
GPIO Pinouts

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