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Forum Index : Microcontroller and PC projects : Radio telemetry link
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| Bizzie Senior Member  Joined: 06/07/2014 Location: AustraliaPosts: 185 |
Hi all, I have started to experiment with a radio telemetry link as used by many drones that are on the market. This one is a 915 MHz system from Banggood. I am surprised how easy it was to get going and the range is excellent (1.3km at 20% power). Here is an image of the simple setup. 
You will note the base station is USB but I would like to use an MM+ instead but have little idea how to wire up the USB and handle the USB comms in the MM+ if it's possible at all. Rob White |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
Interesting little units. What kind of output do you get on the USB base end? IE: Does the computer see the base end of the link as a COM port or some kind of special device? If it sees it as a COM port, then it is quite likely that inside the unit, there is some kind of TTL-USB converter chip. Your best bet would be to bypass that chip, so that you can intercept the data coming out of the link. That idea won't work, if the device ID's itself to the computer as some kind of special USB device. As to the MM being able to act as a USB host for the USB base unit, that is highly unlikely due to the amount of background work that would have to go on, to allow the MM to talk to the USB interface - I don't ever see that happening on any of the current MM models. I might be wrong, but...... Smoke makes things work. When the smoke gets out, it stops! |
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| robert.rozee Guru  Joined: 31/12/2012 Location: New ZealandPosts: 2289 |
from the advert, these units seem to use a Silicon Labs Si4432 to handle the radio transmission/reception, this is a previous generation of the Si4463 used in HC-12 modules that were discussed in an earlier thread. specifications of the two devices look to be pretty much the same, so i would expect similar performance. while HC-12 modules do claim 600m range (as factory configured, 1000m at a reduced baud rate), this is pretty much on a good day, heading downhill, with a tail wind. real-world results will be a tad more modest. having said this, the modules you have from banggood do have more substantial antennaa than what ships with HC-12 modules, which will likely help performance. i'd be quite interested in hearing what sort of range you experience in various flight and on-ground situations. if you are wanting to do point-to-point serial communications, it may be worth looking at the HC-12. these can be had for less than us$10 for a pair on ebay: http://www.ebay.com/itm/171907297975 this will give you a 9600 baud half-duplex TTL serial link between two locations that is transparrent to a micromite (or similar) sitting at each end. i've been using these with great success capturing data from outside GPS modules up to a couple hundred metres away. cheers, rob :-) |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
"I wouldn't be surprised if you got the tun outta this, ya know, on a down-hill run with a brisk northely up ya freckle. Goes like a strangled FART!"  
ID that quote. 
I got my four of these last week. I must see if I can find the time over this weekend to have a play with them. Smoke makes things work. When the smoke gets out, it stops! |
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| Bizzie Senior Member Joined: 06/07/2014 Location: AustraliaPosts: 185 |
Grogster - It is seen as a USB serial port. Manufacturer FTDI robert.rozee - I am looking for ground links only will not be doing any aerial work worst luck. I will investigate your link thank you. Rob White |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
It's probably the FTDI USB-serial chip then. You could tap into the TTL serial where it goes into the FTDI chip, if you wanted to do a module hack. Otherwise, the modules Rob linked to would be worth a try - I am about to play with them myself. Smoke makes things work. When the smoke gets out, it stops! |
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| srnet Senior Member Joined: 08/08/2014 Location: United KingdomPosts: 164 |
I am surprised that some enterprising programmer has not married one of the LoRa modules (RFM98 or DRF1278) with a MM and maybe some C code acting as a serial front end. The LoRa modules are not difficult to drive directly in any case, but have significant advantages over Si4432 or Si4463 based systems. The first advantage is a massive increase in range, around 10 times. These LoRa devices are now in fairly regular use as trackers for high altitude balloons, current maximum distance recorded is around 450km @ 10mW output. That's at 1600bps, expect 3 times that range at a minimal data rate. Second is that these devices operate at below noise level and are relatively unaffected by local RF noise. Third, they are fairly easy to drive as a register device, heaps easier than the Si4432 or Si4463. $50SAT is Silent but probably still working. For information on LoRa visit http://www.loratracker.uk/ |
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