ESP32 precision GPS receiver (incl. RTK-GPS Tutorial). How to earn money with it (DePIN)

Determine your location to the centimeter  around the globe? For everybody, not only for  

the military? Only with an ESP32 and a decent  GPS receiver module? Not possible! Wrong,  

it is possible. You can even earn some money by  building your own base station and connecting it  

to a global network! When I got this board  from Michael, a viewer of this channel,  

I was hooked on the idea of trying and  understanding this relatively new technology. What  

about you? Interested, too? Then, follow along. Grüezi YouTubers. Here is the guy with the Swiss  

accent. With a new episode and fresh ideas around  sensors and microcontrollers. Remember: If you  

subscribe, you will always sit in the first row. By the end of this video, you'll have a clear  

understanding of how it's possible to measure  the distance to fast-moving satellites more than  

20,000 kilometers away and use that information  to calculate your exact position. You'll also  

see how this technology enhances standard GPS. To  demonstrate, we'll use my DIY ESP32 base station,  

connect it to a global network, and see if it can  really deliver centimeter precision. And finally,  

learn what DePINs are and how you can earn money  with this technology. This isn't just about the  

technology, it's about the practical applications  and the potential it holds for us all.  

GPS was invented in the 1970s and implemented  from the 1980s on. In 1995, I had my first  

Garmin handheld GPS receiver for pilots. It  was mind-boggling because from now on, I always  

knew where I was and where the forbidden zones  started. A big stress reliever! The accuracy of  

this degraded non-military system was around 100  meters. Useful for pilots because they use wide  

“airways”, but not yet for car drivers. After the  gulf war, the US military stopped the artificial  

degradation of the GPS signals and so improved its  accuracy. I strongly suggest reading or listening  

to “You Are Here” if you are interested in how  it all began. Other nations like the Chinese,  

the Europeans, and the Russians started to build  their own “GPS” systems. Together, they are called  

“Global Navigation Satellite System”, short GNSS. How does GNSS work? I will use GPS to explain it.  

The most important fact is: In one microsecond,  light and also radio waves travel about 300  

meters and 30 cm in one nanosecond. If we want to measure the distance with  

a precision of 3 meters, we have to be able to  measure time with a precision of 10 nanoseconds,  

and if we want to measure 3 cm, we  need to get to a precision of 100  

picoseconds. Not bad. Keep in mind:  These satellites are 20’000km away,  

move at high speed, and have to have exactly  the same synchronized time. At first glance,  

this seems to be impossible! But let’s  see how they managed to make it work.  

To determine its position, a GPS receiver needs to  calculate the distance to at least four satellites  

by measuring the timing of the signals. For  that, it listens to 1575.42MHz or L1, where  

all GPS satellites transmit their signals. In the  meantime, other frequencies were added, mainly L2  

at 1227.6MHz and L5 at 1176.45MHz. The engineers  back in the 1970s had to solve two main problems:  

1. How to decode very weak signals  traveling 20’000 km through space?  

2. How to distinguish between signals of  different satellites on the same frequency?  

Let’s monitor these three frequencies with  a Spectran SDR receiver. All contain more or  

less random noise with no visible carriers.  Interesting! If I connect the same antenna  

to a proper GNSS receiver module, it shows my  position. Obviously, there are “hidden” signals  

on these frequencies. How does this work? Back then, they decided that each satellite  

transmits its own “pseudo-random” pattern of  1023 bits with a rate of 1.023Mbit/s. That  

is the reason we can hardly distinguish them  from noise. Because these patterns are known  

to all GPS receiver modules, they can compare  the signals coming from all satellites with all  

known patterns. Mathematicians call this process  “cross-correlation”. The result is a peak when  

the received signal pattern and the code of one  particular satellite match in time. Nearly no peak  

is visible for signals of other satellites. So,  such a peak contains two parts of information:  

1. Which satellite sent the signal 2. Its precise timing  

The width of peak is about 1ns or 30 meters. Even  if you can determine the peak very accurately,  

the precision of this signal is limited to a  few meters because there are other sources of  

inaccuracies, as we will later see. This is the  precision of our smartphones, for example. After  

receiving the signals of all visible satellites,  our GPS receiver knows the distance to these  

satellites. But only if the clocks of all  satellites and our receiver are exactly  

synchronized. Keep in mind: A difference of one  nanosecond means already an error of 30 meters!  

This is why all satellites have built-in atomic  clocks that are regularly adjusted by ground  

stations. Our GPS receiver module has a clock,  too. But to save cost and space, not a very  

precise one. So, the whole thing would not work  unless we use a trick that is later revealed.  

The next problem: To get our precise position,  we need not only the distance to the satellites;  

our receiver also needs to know the  momentary position of each satellite,  

also with the precision of meters. We will  later see where it gets this information from.  

To calculate a three-dimensional position,  the distance to at least three satellites  

and their precise positions are needed. The  trick to working with the unprecise receiver  

clock is to use the signal of a fourth  satellite to calculate the precise time.  

Now, we are ready to retrieve the exact  position with a precision of a few meters  

everywhere on Earth. It's incredible,  but it works with a receiver module for  

a few dollars and such tiny antennas. As said before: We want more. 100 times  

more precision. Sounds impossible again!  Let’s try to understand which problems we  

have to solve to get to such a precision: 1. We have to be able to measure the travel  

time of the signal to the picosecond 2. We have to compensate for position  

errors of satellites to the centimeter 3. We have to account for time delays  

influenced by the ionosphere. The ionosphere is  the upper part of the atmosphere and consists of  

charged particles. They are heavily influenced by  the sunlight and therefore change all the time  

4. And correct many more small  errors in the overall system  

Let’s start with the first problem: Increase the  precision of the timing. As we saw before, GPS has  

a modulation frequency of 1Mb/s. But its “carrier”  frequency is around 1.5GHz and, therefore,  

a wavelength of around 20 cm. What if we would be  able to determine where on this wave we are? Then,  

we would know our position to the centimeter!  Technically, the place on a wave is called  

“phase”, BTW. Problem solved? Unfortunately,  not. As shown before, GPS has a precision of  

some meters. Let’s assume a precise GPS position  of 5 meters. Then, 20 wavelengths fit inside these  

5 meters. This is rightly called ambiguity because  we know exactly where we are on the wave but,  

unfortunately, not on which one. Not good! Clever engineers developed real-time kinematics or  

RTK to solve this problem: Let's assume you have  two receivers close together. One is fixed, and  

its position is exactly known; the other can be  moved, and its position is not known. Both measure  

the position with GPS and determine their phase.  Because one knows exactly where it is, it can  

determine on which wave it “sits” and determine  the actual difference between its position  

and the GPS position. If it would transfer this  information to the second receiver, this one could  

determine its exact position, too. And we solved  problems 2, 3, and 4. Because both receivers are  

very close, all these differences are nearly  the same and are included in the “correction”  

signal transmitted. Cool! If we call the fixed  receiver “base” and the second one “rover”,  

we have our RTK system. Of course, it is way  more complex, but for today, we stick with that.  

Fortunately, the distance between the base  and the rover can be up to about 20 km,  

and the system still works. The next problem: How is this  

correction signal transmitted from the base to  the rover? Here, we have four typical scenarios:  

1. Directly by using a transmitter on the base  and a receiver on the rover. High-end lawn movers  

attach a base to the charging station and the  rover to the mover. Also high-end drones work with  

fixed bases close to the pilot. In this scenario,  each rover needs a base station. Commercial base  

stations, unfortunately, cost a fortune 2. Via internet. The base and the rover are  

connected to a service. The base transmits  the correction signal to the platform,  

and the rover receives a valid  correction signal without “owning” a  

base. Signals can be transmitted via Wi-Fi 3. Or via mobile networks. There are many  

such professional services available.  Usually very local and very expensive  

because building and maintaining bases every  20 km is not cheap. RTK2GO is a free service,  

but it only works if you have a base in the  vicinity. The closest one to my home is 40  

km away. So later, I will build my own for  a fraction of the price of a commercial one  

4. Via satellite. Companies like u-blox  operate many base stations around the  

world. Because they cannot afford one every  20 km, they placed them about 150km apart and  

do some math to their signals. Like that, they  typically get a precision of below one meter,  

but not to the centimeter. Still ok for many use  cases and available globally. But not cheap.  

The board I got from Michael offers transmission  methods 2, 3 and 4. The ESP32 includes Wi-Fi,  

and this 4G modem can connect to  the next cellular tower. It even  

contains a satellite receiver that can receive  u-blox data from space. They offer a limited  

service for developers free of charge, BTW. It also contains this small u-blox RTK receiver  

that covers the most important bands, L1  and L2, and shows its position on a map. So,  

let's check how it works. As said before,  I wanted the best precision. So I built a  

base station and connected it to RTK2GO. We go away from the house to reduce signal  

reflections and start with GPS only. As expected,  the position moves a few meters. With RTK enabled,  

this changes considerably. The position is solid.  And if I move the receiver, or should I say,  

the antenna, along a straight line, we see  this straight line also on the map. Impressive!  

Here, you see typical applications  for RTK. Maybe something is for you?  

To build a rover, we just need an RTK-enabled GPS  receiver and an ESP32 if we have Wi-Fi available,  

plus Michael’s Arduino software. Sparkfun  offers many such receiver modules and also  

wrote the required libraries. We know now that RTK works,  

and we saw this rover board. But I also promised  that you could earn money with RTK. How does that  

work? And how can we build a base station? Helium, with its network of LoRaWAN gateways,  

was one of the first companies that created  a new industry called “decentralized physical  

infrastructure networks”, short DePIN.  DePIN companies try to replace investors  

with crowdfunding. Like Helium, they create  a cryptocurrency and pay the owners of the  

infrastructure with this currency instead of  real money till they get paid by the customers.  

Everybody who had to work with professional  investors knows that this would be a very good  

idea for startups because often, these “investors”  are arrogant and a pain in the ass. People who  

watched my Helium video know that I was not happy  about this company. Mainly because there was no  

real business behind transferring LoRa messages.  But is DePIN in general a bad idea? I do not  

know yet because it is too new. But I give it a  chance if there is a real business case behind  

it. Selling RTK correction data seems to be a  multi-million-dollar business already now. So this  

market should be better than LoRaWAN messages.  And its future application is much broader.  

A few DePINs have already tried to get such  networks up and running. One of them is  

Onocoy. This network has two advantages: 1. They allow Makers to create their own  

hardware and do not sell overpriced “miners” 2. Its president is one of the founders of u-blox,  

a no-nonsense guy also with a Swiss accent How can we build such a base station? You need  

four things to get the best signal  and, therefore, the most rewards:  

- A special antenna for all GPS bands - An RTK receiver for all bands  

- An ESP32 - Software to read the receiver  

and send the correction signal to the service You can buy this receiver with an ESP32, but it is  

expensive and only delivers data to Onocoy. This  is why I built one myself. Mine delivers data to  

Onocoy and RTK2GO. I do not show how to build it  here, but you can find links in the description if  

you are interested in this technology. Anyway,  connecting four wires between the receiver and  

the ESP32 board and loading the software is  all it needs. The rest is configuration.  

Keep in mind: Commercial stations cost thousands  of dollars. This miner still costs roughly  

700 dollars, including shipping. My setup was less  than 300 dollars. It's not cheap, but maybe I will  

get the money back or make more than I invested.  It has already started to earn some cryptos.  

Even if I will not earn a lot, I had a good  time learning and experimenting with this  

technology. It helped me understand one of the  key technologies of our civilization, and I pay  

respect to the engineers who, more than 40 years  ago, believed that such a system was possible and  

started to work on it. Keep also in mind that GPS  satellites synchronize most of our clocks and are  

part of each cellular tower, for example. I made  a video on how you can use this precise timing  

for cheap in your lab. Jamming these signals  seems to be a major threat during war times.  

I also promised to tell you how GPS receivers get  the positions of all satellites. The pseudo-random  

code contains a very slow modulation that  transfers all this data, also called “almanac”.  

It can take more than 10 minutes to get all this  data. This is why all GPS modules have a small  

battery attached. They store the almanac data and,  because satellites do not frequently change their  

path, can use “old” data to get a faster fix. If the GNSS receiver has an internet connection,  

like a Smartphone, it uses “assisted GPS” to  get this information much faster directly via  

the internet. This is why your Smartphone  nearly immediately knows its position.  

In this video: - We learned that GPS  

needs extremely precise and synchronized  time signals to measure the distance  

between satellites and our receiver - It needs at least four satellites,  

three to determine the three-dimensional position  and one to correct the time of the receiver  

- Its accuracy is limited by the slow  modulation as well as by variable  

influences by the ionosphere, for example - If we want to get to centimeter precision,  

we need to measure the phase of the carrier signal  as well as account for the real-time difference  

between a precise position and the signal - This difference is measured by a base station  

and transmitted to a “roving” station to enable  the rover to solve the ambiguity and determine its  

exact position. The distance between a base and  a rover should be below 20 km to get an RTK fix  

- Commercial services sell such  correction signals for quite high  

prices. RTK2GO offers a free-of-charge  service but does not have broad coverage  

- This is why I built a base and connected  it to Onocoy, a DePIN company that tries to  

build a global network of base stations and  sell the data for a lower price. I will be  

paid in cryptocurrency for my services. Who  knows if I will get the invested money back  

This was all for today. As always, you find  all the relevant links in the description.  

I hope this video was useful or at  least interesting for you. If true,  

please consider supporting the channel to  secure its future existence. Thank you! Bye