Community Forums

Share:

Looking for technical details of RMT target: What is the IR carrier signal? (Trimble/Geodimeter)  

Page 1 / 4

shu
Posts: 10
 shu
Member
(@shu)
5+ posts
Joined: 6 days ago

I would like to build a custom target that can be tracked by the old dinosaurs Geodimeter 600 / Trimble 5600. I can't find information about the IR LED circuit used in the RMT targets. I would like to know the carrier signal of those IR lights. Maybe someone with an old RMT target can help me out? An oscilloscope and a photocell or directly tapping the IR LED should reveal the the carrier signal. 

My plan is to use an ESP32 micro controller and IR LEDs to recreate the RMT signal, basically an RMT target in a tiny form factor, with a button and wifi connection to another ESP32 connected to the RS232 interface at the total station.

All the best,
Shu

28 Replies
Norm Larson
Posts: 877
Member
(@norm-larson)
500+ posts
Joined: 6 years ago

I also looked at doing this a while back and decided that there were too many used ones on my shelf to make it make sense.  I have been thinking that the S6 active target would make a more suitable effort, at least for me.  I was thinking of using an oscilloscope, but, it is not my field of expertise

Reply
5 Replies
James Vianna
Member
(@james-vianna)
Joined: 9 years ago

250+ posts
Posts: 355

search on here, there was discussion about this a awhile ago, maybe with the guy who plastic prints the prism assembly

Reply
Norm Larson
Member
(@norm-larson)
Joined: 6 years ago

500+ posts
Posts: 877

James, that might actually be me that you are thinking of with the printing, LOL.  I just don't know electronics well enough to use, nor have I ever used, an oscilloscope

Reply
shu
 shu
Member
(@shu)
Joined: 6 days ago

5+ posts
Posts: 10

Hey Norm, if you're still into the idea, I'm happy to guide you to take some measurements. It shouldn't be difficult to hook up an oscilloscope. A simple photocell pointed right at the IR LED should reveal the waveform. 

I would look into the S-series tracker targets if I would have such an instrument at hand. As surveying is not my day job, just a fascinating hobby, I only have a couple 20+ year old instruments. As the active S targets have 8 channels, I'm wondering if they use more than just a simple carrier frequency and actually encode data, like a TV remote.

Reply
Norm Larson
Member
(@norm-larson)
Joined: 6 years ago

500+ posts
Posts: 877

I'm game.  Surveying is my day job, you just wouldn't know it with all of the printed plastic everywhere.  Since the older style RMT and the new active targets use a different frequency or something that makes them non compatible, I can't help but wonder with a few Arduino commands if both compatibility's could be had off the same LED's.  I know that we need to know more to figure that out, but, common that would be cool!

 

So what would be the minimum requirements for a photo cell and a oscilloscope?  Thinking cheap one time use for me at least ...

 

Is something like this sufficent?  I am only reading about half of what the specs are ...

Reply
shu
 shu
Member
(@shu)
Joined: 6 days ago

5+ posts
Posts: 10
Posted by: Norm Larson

I'm game. (...)

Is something like this sufficent?  I am only reading about half of what the specs are ...

I assume the carrier frequency is much higher than the sampling rate of that cheap oscilloscope. From a quick glance at Amazon's sub $100 oscilloscope shelf I discovered cheap ones with a reasonable sampling rate (20 Msps = 20 Megasamples per second), example: https://www.amazon.com/all-sun-EM125-Handheld-Oscilloscope-Channel/dp/B013QQDTFW/

However, I have zero experience in with 'no name' oscilloscopes. I don't know any regular brand that offers such cheap instruments. Do you have a hackspace  or makerspace close by? Maybe visit them with the targets?

Yes, if the carrier and data are within reach for the micro controller we should be able to switch between channels and old/new style with ease. I could make a couple of ring shaped PCBs with LEDs, LED drivers, a small LiPo charger IC, USB for charging... 

In general I think there's still room for innovation on the target end. If there's already a micro controller in there, why not include an IMU? Not for serious work, but for everything else I would love a magic wand with tracker and IMU. Point anywhere with any angle and use the IMU to add the correct vector. Great for undercuts, difficult to reach areas. Way faster than a staff with two prisms mounted in series. Don't you hate it when your assistant shows up drunk? Use the magic wand, no need to have the target plumb 😉

Reply
Norm Larson
Posts: 877
Member
(@norm-larson)
500+ posts
Joined: 6 years ago

Ok, I knew the solution wasn’t going to be cheap tools.  Now I know more of what is needed though.  I am trying to imagine if you had asked me to survey your property with an Amazon total station ....

Reply
shu
Posts: 10
 shu
Member
(@shu)
5+ posts
Joined: 6 days ago

Norm, as you are making your own enclosures for the targets, do you happen to have one torn down or can you take one apart to snap some photos? Macro shots of the PCB would be cool.

Reply
1 Reply
shu
 shu
Member
(@shu)
Joined: 6 days ago

5+ posts
Posts: 10

@Norm, don't bother, Rich just posted a detailed maintenance manual. I'll have a look at that first.

Reply
Richard Imrie
Posts: 1113
Member
(@richard-imrie)
1,000+ posts
Joined: 3 years ago
Reply
1 Reply
shu
 shu
Member
(@shu)
Joined: 6 days ago

5+ posts
Posts: 10

Richard, that's gold. Thank you! 

Reply
Page 1 / 4