Pulse Counting on DM Devices

Pulse counting is available on the following DM devices:

"Optimised" Pulse Counting: Eagle, Falcon*, SensorData LoRaWAN, SensorNode LoRaWAN
Non-Optimised Pulse Counting: Dart2, G62, G120
*Only available on hardware revisions 74.3 and 74.4

TABLE OF CONTENTS

Optimised Pulse Counting on the Eagle and Falcon (Cellular Devices)

Limitations

The pulse count is designed for low power, and applications such as monitoring rain gauges. As such, pulses much faster than 1Hz, with very short pulse widths (<100ms), may not be able to be detected reliably. However using a shorter debounce time can allow for faster pulses to be counted. So keep this rough limit in mind, and test prior to deployment if you expect fast pulses.

Maximum Values.

Analogues 1 to 10 are 16 bit), so the count can range from -32,768 to +32,767
Analogues 11 to 20 (32 bit), they range from -2,147,483,648 to +2,147,483,647.

Resets and Count Overruns

Pulse counts are stored in flash memory, so should not be lost should power be lost. They may be reset during a firmware upgrade. If a user wishes to reset the pulse count, this must be handled on the server.
One way to handle resets occurring due to an overrun or FW update, would be to determine if the count goes down from a previous value, ignore any counts from the last value, but start again from the new one. for example, you get 4, 7, 10, 30, 10, 12, ignore the 30 -> 10 difference and start from 10. so it would be 30 + (10-12) = 32

if ( value[n] < value[n-1] )
{
newValue = value[n-1] + value[n + 1] - value[n];
}


Parameter Setup

To set up a Digital input to measure pulses on input 1, you can follow the below parameters

Function 
Set to Digital Input. There is a "Rain Gauge" option, but in general this should not be used (even for rain gauges, confusingly) - see why below
Logging and Uploads
In general, Logging and uploads should be disabled to save data on higher frequency pulse sources and accurate timestamps are not required. Heartbeats (see 'Basic Tracking') can be used to periodically upload counts every X minutes/hours.
Active Level
The active level will depend on how your application applies to pulse counting. For more information on Active levels, See our article here
Bias Resistor
See our Article here
Debounce Time
This field is used to determine your debounce time (time input needs to be stable for the pulse to be registered). This is useful for filtering noisy inputs, but also has a direct relation to the shortest pulse widths/highest pulse frequencies that can be measured. If pulses aren't being counted, try lowering this value. If a lot of errant pulses are counted, try increasing it.
Rising edge Count:
see next section below. 
Analog Input:
Chose analogue number to store count in, 1-20. Inputs 11-20 have a higher maximum pulse count due to being 32 bit vs 16 bits for inputs 1-10.



Rising Edge Counts

Rising Edge Count
Yes or No

If you want the pulse counter to increase the count on the rising edge which is the first green line, set to yes, if you want the count to increase on the falling edge, set to No.


Example Cellular Device Payload

An example of the pulse count coming through on analogue 17. The count will simply appear in Field ID 6 or 7 (analogue data fields), in the whatever analogue is chosen in parameters:

 {
"AnalogueData": {
"1": 4294,
"3": 3331,
"4": 99,
"5": 4200,
"6": 9984, // %Battery remaining
"17": 5 //Pulse Count
},
"FType": 6 // Field ID# - DMT-Data-Fields.pdf
                }

How do I count pulses from a rain gauge/flow meter on the Eagle or Falcon?

So, with the information above, for a tipping rain gauge (or other device) which generates pulses, to configure we need to:

  • Connect the rain gauge
  • Ensure the Function is set to Digital Input
  • Select a rising or falling edge count and debounce time. 
  • Then the count of pulses appears in the Analogue input we have set (or 17 by default). 
  • If we are expecting a lot of pulses, we probably don't want a "Digital Input Changed" log for every single pulse. So if that is the case, ensure to set Log On Active and Log On Inactive to No to avoid getting all of these logs. 

The "Rain Gauge" Digital input function is a specific feature set and results in this behaviour when set:

  • When a digital input change is detected the log reason is "Rain Gauge Tipped" - and the only fields uploaded with the log are the Digital Inputs (and not the analogue inputs) 
  • So we don't actually get the count uploaded with each tip as it is in the analogue fields - so this option should be avoided (it exists for a specific customer use case)

Pulse Counting on the SensorData and SensorNode LoRaWAN®

The same limitations and caveats apply. However configuration is simply slightly different and is covered in the relevant guides:


"Non-Optimised" Pulse Counting on the Dart2, G62 and G120

The Dart2, G62 and G120 are primarily vehicle trackers and as such were not designed with pulse-counting as a primary feature/function. So there are caveats to the operation. It may be useful in some applications, and these devices might be desirable for other features meaning they are selected. 

Parameter Setup

Parameter set up is as above for the Eagle and Falcon, with a few caveats:

  1. The function must be set to Pulse Counter
  2. The Config parameter sets both the analogue where the count is stored, and the debounce. 
    1. If analogues 1-10 are selected, the debounce time is 10ms
    2. If analogues 11-20 are used, the debounce time is 20ms

So for all intents and purposes, the "Pulse Count" on these devices is effectively just a fast edge counter, that will not support counting fast pulses reliably. Additionally, the count is not stored in non-volatile memory, and will be lost on a device reset (i.e. parameter change, firmware update, power loss) 

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