Keep-alive

The keep-alive is a periodic message sent by the HT Display Lite with sensor data and more. In this page you will learn how to decode keepalive messages and how to set the keepalive interval.

Keep-alive decoding

Periodically sent message which contains the most important device data.

The data is described in the table below, where an example is also given in a second table.

Byte	Bit Index	Value	Meaning
0	-	01	Command byte for this packet.
1	-	XX	Internal temperature sensor data, bits 15:8 – T[15:8].
2	-	XX	Internal temperature sensor data, bits 7:0 - T[7:0]. t [°C] = (T[15:0] - 400) / 10
3	-	XX	Relative Humidity data; RH [%] = (XX * 100) / 256
4	-	XX	Device light intensity data, bits 15:8.
5	-	XX	Device light intensity data, bits 7:0. Light intensity [Lux].
6	-	XX	Device battery voltage data, bits 15:8.
7		XX	Device battery voltage data, bits 7:0. Battery voltage, [mV].
8		XX	Power source status. Тhe device is powered by: 0x00 - Built-in photovoltaic panel; 0x02 - USB power supply.

Keepalive example

Byte	Bit index	Value	Meaning
0	-	01	Command byte for this packet.
1	-	02	Internal temperature sensor data, bits 15:8 – T[15:8].
2	-	88	Internal temperature sensor data, bits 7:0 - T[7:0]. t [°C] = (T[15:0]-400)/10 t [°C] = (0x0288-400)/10 = (648-400)/10 = 24.8 deg C.
3	-	80	Relative Humidity data; RH [%] = (XX*100)/256 (0x80 * 100)/256 = (128*100)/256 = 50% RH
4	-	02	Device light intensity data, bits 15:8.
5	-	7A	Device light intensity data, bits 7:0. Light intensity [LUX]. 0x027A = 634 LUX
6	-	0A	Device battery voltage data, bits 15:8.
7	-	45	Device battery voltage data, bits 7:0. Battery voltage, [mV]. 0x0A45 = 2629mV
8	-	00	Power source status. Тhe device is powered by: 0x00 - Built-in photovoltaic panel;

Keepalive period

SET

Byte index	Hex value - Meaning
0	02 – Command code to set keepalive period
1	XX – keep-alive period in minutes. Value 0x00 isn’t applicable. Default value 0F=15min.

Example command: 0x020A

The example sets the keep-alive period to 10 minutes.

Note that the period value must respect the LoRaWAN messages duty cycle limitations. Otherwise the message will be sent when this is allowed. Also, the bigger period value, the less battery discharge. In most of cases, min. allowed period is 3 minutes and recommended values are 10 minutes or greater.

GET

This command is used to get the period of the keep-alive command messages. Server sends the command code and the response is sent from the device together with the next keep-alive command.

The keep-alive in the example is omitted for clarity.

Byte index	Sent request	Received response
0	12 – The command code.	12 – The command code.
1		XX – device keep-alive period in minutes.

Example command sent from server: 0x12;

Example command response: 0x1209 – the keep-alive is 9 minutes.