I have a data gathering device and it functioning mostly. I use two arduinos sharing an sd card. One arduino is used for data collection from various sensors and also takes a very low resolution jpg picture (about 7K) and stores it all on the sd card. When data collection is finished the sd card is electronically switched to the arduino that operates the radio to send the data. This entire part works perfectly. On the radio arduino I am using the Radiohead library. The data can be transferred successfully however due to the limitations of the radio the jpg image is a problem. Of course I can convert the small image to hex for transfer. I need to use nearly the slowest radio transfer rate inorder to get the range required. What would the proper approach to the transfer of the picture data be? Is there a better picture format to use for this purpose?
Why is the post entitled 'RFM95 LoRa radio', are you using one ?
I need to use nearly the slowest radio transfer rate inorder to get the range required.
No doubt you know what that means so can you explain for the benfit of the forum, for instance how far do you need to transfer the data and where is the location ?
Perhaps provide details of the actual project as well ?
The path loss will be about 125db so that will leave me with very little fade margin. The unit is completely functional now with the exception of the transfer of the jpg image. My question is: How do I transmit a very small jpg image using a Rfm95 Lora radio? Receiving is no problem. I just pass the receive data to an iOS or android device via Bluetooth for processing.
trotterlg:
The path loss will be about 125db so that will leave me with very little fade margin. The unit is completely functional now with the exception of the transfer of the jpg image. My question is: How do I transmit a very small jpg image using a Rfm95 Lora radio? Receiving is no problem. I just pass the receive data to an iOS or android device via Bluetooth for processing.
A path loss of 125dB is a very lonk link, like I mentioned before some details would be useful.
Transferring a file\image via LoRa is no different to using most of the packet based RF devices, you send it in a number of discrete packets, but in your first post you said;
"the data can be transferred successfully however due to the limitations of the radio the jpg image is a problem"
Ok so for what it’s worth this is the software development board for a cubesat. With no Fernell zone the radio has the link budget to make a 500kl path with the use of a moderate gain antenna on the ground.
Now my real question would be for a little code snippet to send a 7K jpg file from one radio to another. I can successfully send data from temperature, spin rate and power supply voltage but not the picture file. All of the other technical difficulties have been successfully solved.
The issues around transmitting the image itself are not really specific to LoRa, and I doubt the required software it just a 'snippet'.
First the picture has to be split up into a number of discrete packets and each one sent in the first instance. A simple send and acknowledge for each packet would obviously work, but its likley to be slow. This is why context is so important, send and acknowledge might well be practical on terra firma, but from a low power satellite ?
Perhaps better to broadcast all the packets (some of an image is better than none) and then have protocol to tell the transmitter which bits are missing. In this way you can then use a number of spaced groundstations (which increasing the chances of reception) with each contributing to the receipt of the overall image as some might get one bit some another etc.
A very similar approach has been used by UKHAS to get images back from high altitude balloons, they may have published the software for that.