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Very long range remote telemetry using LoRa Repeater

Status: Proposal
August 3, 2016
in Elektor magazine | May 2018 | Find it here
Remote telemetry on LoRa-433 MHz repeater

Long Range remote repeater works both ways on line-of-sight. Runs on 3.3 volt, LCD is optional on 6volt supply. Consumes around 100 mw power.

Coal based thermal power plants are amongst the greatest polluters of the present time (next to automobiles). To keep these polluters in check, NGT (National Green Tribunal) plays an important role. They not only insist on control of pollutants but also insist on measurement and monitoring at the source of pollution.

One such problem area is ash dyke over flow lagoon water level. Ash produced out of burning of coal is mixed with slurry and then transported to the ash dyke where it is stored in ash pond submerged under water. The surplus water is spilled over into the adjacent overflow lagoon and there from it goes into the ash water recirculation pump house. Water is pumped back to the power house again. Thus, besides saving of water this also helps reducing discharge of polluted water into the natural drainage system.

Hand held Remote receiver, can be connected directly to the serial monitor – gtkterm,picomonitor or putty

Uploader: Hand held signal uploader

During normal day operation all the water that spills into the overflow lagoon is pumped back to the power house however, during heavy rain or pumps problem when the water level increases there is possibility of ash water spills the overflow lagoon and enters into the natural drainage system. Besides keeping the ash water recirculation system healthy NGT also wants to monitor the ash slurry overflow lagoon water level on a 24*7 basis.

Well, this command is not yet passed as a statutory requirements but in the coming days sure, it will. Already the emission from power house chimney – Sulpher oxides (SOx), Nitrogen oxides(NOx), CO2 and suspended particulate matters are displayed in public domain.
... ... ...
The ash water lagoon is happened to be situated some 10 to 15 kms away from a typical power house while the ash slurry control room is located at the foot of the power house. The ash water recirculation pump house is located somewhere near the ash dyke but certainly it has the distinct disadvantage of monitoring the lagoon water level. It gets water from either through a channel or through a long pen stock and then discharges through massive water pipe lines. The overflow lagoon water level may be brought into this pump house but this pump house is not a priority location therefore, for 24*7 monitoring the level is to be brought into the main ash slurry control room which is there inside the power house campus.
Bringing water level to such a great distance is not only a difficult thing but itself is a challenge. But armed with LoRa technology we took up the challenge and moved towards an achievable solution.

The project stated here can be used for many other generic remote telemetry / repeater monitoring operations.

Principle: It has been seen that LoRa on 2dBm to 13dBm emission power in LOS can comfortably transfer data from far ash dyke to the boiler head of Unit-X, which is at 65 meter height. Every damn thing is in LOS from here. But the ash water control room is a just one story building located 1.2 km away from the foot of this boiler. Therefore, in the first step the data is made available at 65 mtr height of Unit-X boiler. Now this data which is a 32 byte serial data comprises of water level, temperature and air direction (in the near future) is transfered to another LoRa connected on the same Arduino but on UART so that not much processing power is required. The 2nd LoRa is an UART model emits on 433 MHz but with different ID numbers. [Different windows based software is used for creating / setting ID numbers – ID & channel number should be same for both the UART modules].

The 3rd Arduino which is the final destination of data is housed on the roof of the Ash water control room.In one word the device that we are going to place on the Unit-X boiler is nothing but a repeater built on LoRa !

[LOS=Line Of Sight, LoRa is the trademark of Semtech's Long Range Spread Spectrum Modem technology]

01. LoRa 433 mhz transceiver module – 02 nos $20.00 link:
02. Arduino clone or ATMEGA328P-PU – 03 nos $4.50
03. DS18B20 ,water proof -01 no $1.20 link:,searchweb201602_3_10037_10049_10017_405_404_407_10033_406_10032_10040,searchweb201603_7&btsid=4c2bf2d0-c91b-490c-8bb6-a1e1e3f16975
04. Ultrasonic probe: for level measurements.
05. 433 mhz 6 dBi rubber antenna – 02 nos $4.5 link:
06. SMA female plug – 02 nos $3.0 link:
07. LoRa -SX1278 on UART – 50$ a pair link:

The LoRa module has the pin up connections of 2mm pitch , which may cause problems while connecting them on standard PCB of 3mm pitch.

RFM98 E32-TTL-500
[Both uses SX1278 chips but the first one is from Hope while the 2nd one is from EByte]

Field Testing: On the penultimate day the sky was overcast with monsoon cloud since morning. I sent my supervisor Shukla with my zeep to the ash dyke while I took position at Unit-X boiler with the repeater module and my colleague, Lalit was sent on the roof of the ash water control room with the hand held unit in his hand.

The signal stated pouring in the moment Shukla switched the sender unit on while he was still sitting inside the jeep. Only he was holding the sender unit near the jeep's window facing the Boiler-X where I am standing.

Gradually he moved towards the farthest end of the Ash dyke which is as per my GPS calculator 14.2 kms away from where I'm standing. Standing on the edge of the overflow lagoon he faced the ultrasonic level gauge towards the milky white ash water level and the reading showed 2.2 meter from Shukla's height. Shukla has to be careful now as I told him over mobile because earlier I saw a crocodile on this lake and today being a cloudy day the crocs may come over for sun bathing !

Below on the roof of the ash slurry pump house I find Lalit is waving his hands which means he is getting the reading. The ash slurry pump house is about 1.5 km diagonally from here. Before I could recognize him from here, Lalits call came in and he was exuberant to declare that he is officially announcing that our dyke's water level is now under 24*7 scanning.

I told him to monitor the seconds display and as per him the data was coming in a gap of 2 seconds to 3 seconds. I moved towards the diagonally opposite corner of the boiler where from Shukla was still in LOS while Lalit was behind the adjacent Boiler but he was still getting the reading with slight increase in the gap (3 seconds to 4 seconds).

This is the time when heavy rain started at dyke end. Shukla moved inside the vehicle while he held the antenna outside the window. I was still getting data but the gap increased to 3/4 seconds now. The rain got so heavy now that Shukla had to shut the windows. The data stopped for sometime but again it started coming in with long gaps of 7 seconds. Below me, Lalit was receiving at the same frequency.

Gradually the rain started over here and I became the 2nd causality. The heavy rain with storm at this height was quite an experience to feel. The downpour was lashing me from every side. I moved towards the elevator when Lalits call came in.

He has now moved to the safety of the ash slurry control room. He shouted that he was still getting data but at a gap of 7 seconds to 11 seconds. Obviously I was not at LOS with him. Before entering the elevator at 19th floor I called both Lalit and Shukla to abort the test.

Schematic: Schematic will be for Uploader, Repeater & the Downcomer. Uploader: Uploads – Temperature, water level & GPS data

Repeater: Repeats Temperature, Level, server ID & GPS Data

Downcomer: Redisplay data

1. Ash dyke uploader – This uploads temperature, level, time, date and other GPS data 2. Ash dyke repeater – This repeats the above data at LOS with the uploader. 3. Ash dyke downloader – This redisplays data at LOS with the repeater.

Bera S
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Repeater schematic
Down comer schematic
Uploader schematic
Prototype uploader
Prototype Down loader (hand held)
Prototype Repeater
Hand held LoRa Transmitter
Handheld LoRa Transmitter
Ash dyke repeater schematic - modified
Ash dyke downloader schematic - modified

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