Common Concepts - Digital Inputs

TABLE OF CONTENTS


Background

Digital Matter devices commonly have digital inputs. 

These inputs detect the voltage at the input, check it against the threshold, and then record this as on "1" or off "0" and report to the server. This can be used to determine the state of an asset for example:


Digital Input Specs

Check the relevant device datasheet to confirm - but all devices have the same circuitry for digital inputs, meaning the following specs apply:

  • Input voltage range = 0-48V. This can technically be exceeded without damaging the device, but the input will not work properly outside of this range. 
  • On/Off Thresholds
    • Pull Up Enabled
      • Input registers low/off below 0.8V
      • High/On above 1.0V
    • Pull down enabled
      • Registers low/off below 2.0V
      • High/On above 2.4V

Bias Resistors

Many digital inputs in the Digital Matter product range have a settable 'Active Level' and a configurable Bias Resistor. 

  • The Active Level determines the physical line level (high or low) at which the input is considered on. 
  • The Bias Resistor essentially determines the state of the input when nothing is connected to the input. Since often we would leave them disconnected, or 'open circuit' meaning the state isn't well defined. The bias resistor handles this.

There are 3 options:

  1. Pull up: pull the input high. 
  2. Pull down: pull the input low
  3. Disable: do not bias the input.
These options are useful when one of the states being read is open-circuit (disconnected/high impedance). In this case, enable the bias resistor setting in the opposite state to the level being switched to.  This is commonly used when working with an "open collector" output. The pull up/down is a "weak" pull up/down.


Results of different configurations. 

Bias ResistorActive HighInputResult
 Pull DownTrueLowInactive


HighActive
Pull DownFalseLowActive


HighInactive
Pull UpTrueLowInactive


HighActive
Pull UpFalseLowActive


HighInactive

Set Up

To set up, we first need to check our device Getting Started Guide for the harness definition, to find out which wires correspond to the correct digital input. Then we can add the parameter tab to apply the right settings. See OEM Server - Getting Started for how to adjust parameters.

Function and Digital InputLeave as Digital Input. It can be set to Pulse Count for Pulse Counting - in this case refer to Pulse Counting on DM Devices

Bias Resistor and Active Level See table above and examples below for what to set. 

Log/Upload on Active - By default, the device will only log a record when the input changes. It is not immediately uploaded. In most cases we want to turn this on. So set Upload on Active/Inactive to Yes

Buzzing Parameters - We can optionally have any buzzers connected buzz to notify us the input is on/off. See section below on buzzing. 

Config 1 - Debounce Time - so by default, the input must stay on continuously for 1000ms = 1sec for the device to register it as on and send an update to the server. 


Example - Panic Button

A panic button is an example of a "Dry Contact" device. Dry contact is a synonym for 'no voltage'. Since to detect the push button closing, we aren't needing to provide any power. We are just detecting when there is a complete circuit, and when there is an open circuit. 

We set up with a a Normally Open push button switch, one side connected to the input and the other to ground.

In this configuration, when the button is OFF it is

  1. Not pressed
  2. an open circuit, 
  3. and there is no complete path from the input to ground. 

When the button is ON it

  1. Is pressed
  2. closes the loop.
  3. Connects the input to a low signal (GND)

The configuration would be:

  • Bias resistor set to 'pull up.'
    • When the button is not pressed (OFF) and nothing is connected to the input, the input is held high (so we consider this level 'off' (active level = low)
  • The Active Level is set to low
    • When the button is pressed (ON) the input is pulled to ground.
    • The digital input is considered on when the button is pushed.
  • We want immediate notification of duress button pushes, so we set Log on Active and Log on Inactive to Yes.


Example - Monitor a PTO/Pump/Engine

In this case, our digital input we want to set up in the same way as our dedicated ignition input (i.e. the white wire on devices). We consider the input 'on' when there is voltage present at the input (a high signal), and off when there is no voltage. 

We would connect a device ground wire (any black wire) to ground on our asset, and a digital input wire to the high side of our pump/pto etc. Wherever will register above 2.4V when on, and below 2.0V when off.

The configuration would be:

  • Bias resistor set to 'pull down'
    • When not running, there is no voltage present on the input. It is held low.
  • The Active Level is set to high
    • When running, there is a high voltage signal at the input.
    • The digital input is considered on. 
  • If we want to know in real-time if we are on or off, we should set Upload on Active and Upload on Inactive = Yes.

Buzz on Active/Inactive

We can configure the device to sound any connected buzzers, or flash an LED when the input is active/on or inactive - off. 

This can be very useful for providing feedback to drivers/operators, for example:

  • Sounding a buzzer when a seatbelt is undone or a tailgate is open
  • Sounding a buzzer when a duress button has been pressed, to provide feedback that it was registered (note this doesn't confirm it has been received by the server). This can also help prevent false alerts as drivers are notified of accidental presses and can contact response teams. 

See Common Concepts - Buzzer/LED Setup - for how to wire and configure the output parameters for a buzzer. 

Then we can configure buzzing with these parameters. Setting the count to 255 enables continuous buzzing, for the entire time an input is on/off. 


Example - 3 beeps when an input goes active. 


This would result in - when input goes active:

Buzzer on 20ms -> off 20ms -> on 20ms -> off 20ms -> on 20ms -> off 20ms


Example - Continuous buzzing when an input is on, long buzzes (500ms on/off)


Buzz only when the ignition is on

We may want to set up the device to buzz when an input is active, and the ignition is on. i.e. we want to buzz if the tailgate is left open and the engine is running. We can solve this in hardware, by simply setting up the buzzing as before, but connecting the positive terminal of the buzzer to the ignition source/barrel. 

Then, we are only ever providing power to the buzzer when the ignition is on, so it doesn't matter what the switched ground output is doing in this case. Then once the ignition is on, if the digital input is also on, the buzzer can sound. 


Advanced Features

For advanced functionality, check out the Input Monitor feature, available on the G120, G62 and G100. 

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