We have encountered requests regarding the solution for high-temperature remote readings, that could go up to +120°C but also would measure humidity. This use-case can be found in HACCP applications, in the monitoring of warehouses or anywhere, where the information about temperature and humidity is crucial. The biggest challenge lays in the low-power nature of the solution since the LPWAN network will be used.
This application can be implemented using ACR-CV-101N-R-D converter and this converter is also being used in this application note. The ACR-CV-101N-R-D converter is communicating over NB-IoT, has a non-powered RS485 bus and D battery with a capacity of 17 000 mAh.
A more suitable option would be using ACR-CV-101N-R12-D converter, which has powered the RS485 bus by 12 volts. The temperature and humidity probe being used can hold anything between 3.3 - 24V.
| Wiring of the temperature probe | |
|---|---|
| Red | Power + 3.3…24V |
| Black | Power - |
| Green | RS485- (B) |
| Yellow | RS485+ (A) |
| Communication | |
| Baud rate: | 9600 as default |
| Data bit: | 8 |
| Stop bit: | 1 |
| Parity | None |
| Modbus ID address: | 1-255, default is 1 |
| Protocol | Modbus RTU |
| Function code: | 03 (Read), 06 (Write) |
| Specification | |
| Power supply: | 3.3..24VDC |
| Temperature meassuring range: | -40..+120°C |
| Humidity meassuring range: | 0-100% RH |
| Temperature accuracy: | 0.3°C |
| Humidity accuracy: | 3% RH |
| Measurement resolution: | 0.1°C, 0.1%RH |
| Working current: | 0.9mA |
| Sleeping current: | 18uA |
| Power protection: | Anti-reverse connection ± 15kV ESD surge protection |
| Refresh interval: | >=20ms |
| Baud rate: | 1200,2400,4800,9600,11400,19200 |
| Cable length: | 1 meter |
-----------------------
--- CONFIGURATION -----
-----------------------
----- NB-IoT ----------
APN = "nb.m2mc"
PLMNID = "23003"
protocol = "UDP" -- UDP or TCP
ip = "192.168.0.20"
port = 4242
receiveTimeout = 500 -- the maximum execution time in milliseconds
------ Timing ---------
-- device wakeup interval
periodHours = 0
periodMinutes = 5
-----------------------
-----------------------
-- CONFIGURATION END --
-----------------------
function onWake ()
api.rs485Setup(9600, 0, 1, 8)
dataToTransmit = ""
--read temperature
api.rs485State(1)
api.voltageSourceState(1)
api.delayms(500)
req = pack.pack('<b8', 0x01, 0x03, 0x00, 0x01, 0x00, 0x01, 0xD5, 0xCA)
api.rs485Receive(0) -- flush input buffer
api.rs485Send(req)
ans,len = api.rs485Receive(500)
if len == 7 then
dataToTransmit = dataToTransmit .. 'T' .. ans:sub(4,5)
temperature = string.byte(ans:sub(4,4))*256 + string.byte(ans:sub(5,5))
if temperature > 0x7FFF then
temperature = -1 * (0x10000 - temperature)
end
temperature = temperature/10
print("Current temperature is: " .. tostring(temperature) .. "C")
end
-- read humidity
req = pack.pack('<b8', 0x01, 0x03, 0x00, 0x00, 0x00, 0x01, 0x84, 0x0A)
api.rs485Receive(0) -- flush input buffer
api.rs485Send(req)
ans,len = api.rs485Receive(500)
if len == 7 then
dataToTransmit = dataToTransmit .. 'H' .. ans:sub(4,5)
humidity = string.byte(ans:sub(4,4))*256 + string.byte(ans:sub(5,5))
humidity = humidity/10
print("Current RH is: " .. tostring(humidity) .. "%")
end
api.voltageSourceState(1)
api.rs485State(0)
-- send data to LoRaWAN/NB-IoT
api.dumpArray(dataToTransmit)
if #dataToTransmit < 1 then
buf = "NO DATA RECEIVED"
else
buf = dataToTransmit
end
print("To NBIOT: ")
api.dumpArray(buf)
print("Sending to NB-IoT")
api.nbSend(ip, port, buf, receiveTimeout, protocol)
print("Done sending")
print("Sleep now, wake in " .. tostring(periodHours) .. "hrs:" .. tostring(periodMinutes) .. "mins.....")
api.wakeUpIn(0,periodHours,periodMinutes,0)
end
function onStartup()
print("Starting up NB-IoT Abest Modbus script with APN settings")
result = api.nbAT("AT*MCGDEFCONT=\"IP\",\"" .. APN .."\"", 5000, 1)
print("APN result: " .. result)
result = api.nbAT("AT+COPS=1,2,\"" .. PLMNID .."\"", 5000, 1)
print("PLMNID result: " .. result)
end
[17:41:28:193] SYS: —- New request —-␍␊
[17:41:28:193] SYS: Battery Voltage: 3679 mV␍␊
[17:41:28:193] LUA: starting lua script version 1␍␊
[17:41:28:865] LUA: Starting onWake() script␍␊
[17:41:29:489] ~>Current temperature is: 28C␍␊
[17:41:29:601] ~>Current RH is: 40%␍␊
[17:41:29:617] ␍␊
[17:41:29:617] ⇥ 00 : 54 01 1A 48 01 92 ␍␊
[17:41:29:633] ~>To NBIOT: ␍␊
[17:41:29:633] ␍␊
[17:41:29:633] ⇥ 00 : 54 01 1A 48 01 92 ␍␊
[17:41:29:649] ~>Sending to NB-IoT␍␊
[17:41:30:241] NBIOT: wake the module up!␍␊
[17:41:31:089] NBIOT: wake the module up!␍␊
[17:41:31:441] NBIOT: Signal level 21.␍␊
[17:41:32:641] NBIOT: No return data␍␊
[17:41:38:672] ~>Done sending␍␊
[17:41:38:720] ~>Sleep now, wake in 0hrs:5mins.....␍␊
[17:41:38:742] SYS: date / time - 2020/10/12 / 17:41:37␍␊
[17:41:38:742] SYS: wake up at day / time - 12 / 17:46:37␍␊
[17:41:38:751] LUA: destroyed all lua objects, exiting␍␊
[17:41:38:751] SYS: entering sleep mode␍␊
Oct 12 17:34:36 challenger python[31631]: 2020-10-12 17:34:36 diff = 21:07 : received message from: ('46.234.125.38', 59164) in hex: 54011C4803D4
The payload captured on the server side is “54011C4803D4” in hex. The first and the fourth byte stand for temperature and humidity. After we convert “54” from HEX to ASCII, we get “T”, which stands for temperature. The “48” is “H”, which stands for humidity. The “011C” and “03D4” are temperature and humidity values. After translating the whole payload, we get T284 H980. Temperature is 28.4°C and humidity 98%RH.
| Payload | |||||
|---|---|---|---|---|---|
| Byte | |||||
| 1 | 2 | 3 | 4 | 5 | 6 |
| 54 | 01 | 1C | 48 | 03 | D4 |
| “T” | Temperature value*10 | “H” | Humidity value*10 | ||