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Post by G4EWJ » Thu Sep 14, 2017 11:51 am

DigiTwist is an experimental 2 axis satellite tracker, primarily for the HamTV transmitter on the ISS. 2 broadcast satellite dish positioners are connected together and are controlled by a dual Diseqc pcb.

I've started to put details on the BATC Wiki: https://wiki.batc.tv/DigiTwist
Circuit diagrams and software will appear shortly.

The most difficult part is the drilling of the complex shape of the positioner rotor arm in the joiner bar. Quotations are currently being sought for production of a batch. To gauge demand, it would be helpful to register an interest by PMing or emailing me. my callsign at yahoo dot com


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Re: DigiTwist.

Post by G4EWJ » Wed Sep 20, 2017 12:36 pm

I have the parts list ready for the test pcb. I didn't make a note of who had a pcb or joiner bar at CAT17, so please could you email me and remind me.
my callsign at yahoo dot com


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Re: DigiTwist.

Post by G1BVI » Wed Oct 11, 2017 12:51 pm

For Anyone interested in building this project, I found a single TM-2600 at £41.25.
This is from
https://www.world-of-satellite.co.uk/Te ... tal-Geared

There may well be other cheaper options but this is the best deal I have managed to find.

I have nothing to do with this company, but will be placing an order soon.



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Re: DigiTwist.

Post by K6REA » Tue Nov 07, 2017 1:55 am

Hi Brian,

I see where to get the one motor, but where can i order the rest of the parts needed for this device ?

kevin rea
Lancaster, Calif. USA

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Re: DigiTwist.

Post by skdi » Fri Nov 10, 2017 4:25 pm


my understand is that the project is work-in-progress and there is no single place to get easy everything necessary, at least for the time being.

However, let me tell you, as someone who is excited to get the project running as soon as possible and who is outside the UK (but in Europe), my experience so far:

1) 2 x TM-2600 M3 motors: those are "Designed in the UK, Made in Taiwan" and I guess that's why I was not able to find them outside the UK. So, I purchased them from the link provided couple of posts above. Not a pleasant experience though:

1.1) the weight of two such motors with packaging is 7.5 kilograms and the cheapest shipping even to another European country cost me 30 USD (and it was very slow, basically the parcel was traveling with trucks across Europe)

1.2) even the motors are "brand new" one of mine looks like it was used or at least mounted once, i.e. having small scratches on its body and mounting elements, but that's not really a problem - probably even after the first mount I will make the same if not even worse marks on it.

The other one look really like new, no scratches on its body and mounting elements, but it has even worse problem - there is big crack in the motor housing body - the alloy looks so strong and massive, I cannot imagine what kind of force can cause the crack - maybe it was some structural defect in that particular alloy of the housing body. Anyway, in normal circumstances I would return that one, but because of the heavy weight and shipping costs, ended up with just putting silicone glue to seal the crack to prevent water (from rain, etc) entering the motor body when it's mounted outside.

I don't know, if I had bad luck or quality control of those motors is questionable... or maybe they do not consider those "cosmetic" defects a fault...who knows...

2) if you ask me (that's my opinion and others can correct me if I am wrong), you can use any 2 identical DiSEqC motors that support DiSEqC v1.2, which protocol defines the commands to instruct the motor to move X degrees in one or another direction. Possibly, the only limitations are speed, in case there are DiSEqC 1.2 motors that are not moving fast enough to track the ISS and maximum weight such motor can move - because especially the one of the motors is very heavy loaded - it carries the other motor, the joiner bar and the dish. Last, consideration here is the "joiner bar" itself as it will be most likely different one (needs different holes) for each motor model/brand, see point 3.

3) the "joiner bar" : currently you need to make one for yourself, there is no even such bar ready available for TM-2600 M3 motor. that I guess is another point to just use another motor model altogether. in fact for TM-2600 M3, the joiner bar contains complicated shapes that need to be cut in the metal, which is disadvantage in making such bar easily. So, by taking measurements on my TM-2600 M3 motors and with help by Brian (giving me some measurements of the "proof-of-concept" bar they made), I designed (with help of a friend) computer 3D model in STEP format of that bar, which is compatible with HAAS CNC milling machines. Maybe that's actually machine-independent, I don't know, not an expert in the field. However, manufacturing even a single piece turned out to be very expensive and I am looking for another manufacturer with such machines. I don't share the computer model I made here, because it's not proven to be correct - that will be clear after at least one piece is made. Anyone with access to CNC machine compatible with 3D model in STEP format, feel free to contact me. I am attaching few pictures of my 3D computer-generated model.
01_bar.jpg (35.77 KiB) Viewed 3325 times
02_rear_face.jpg (30.19 KiB) Viewed 3325 times
03_rear_face_mesh.jpg (44.79 KiB) Viewed 3325 times
4) Other parts you need:

4.1) Arduino Nano V3 - that's the blue board on top of the green one on the picture in the Wiki:


At least I found it only from China - costs 1.85 USD shipped, but it takes 30-60 days to arrive. So, if you don't have one, considering it's cheap, grab few, because until they arrive probably the project will progress further.

4.2) 2 x RT5047A : that's the DiSEqC controller on the board. It's Taiwanese chip and not available in Europe - at least I was not able to find it - available in the US and China though - I got it from China, because it's 3 times cheaper than getting it from the US: 5 pieces from China cost me 3 USD shipped. I don't know what was the motivation RT5047A to be used, because for example LNBH26 is made by STMicroelectronics, i.e. European company and it's Dual-chip, i.e. instead 2 you need just one and cheaper than 2 x RT5047A (and that taking RT5047A price in China, 2 x RT5047A are like 4 times more expensive than LNBH26 if buy from US). So, there are cheaper and better available parts, unless RT5047A was not selected for some special reason(s).

4.3) "hex key with extra long arm" : size "6", that means 6mm between any 2 parallel sides of the hex shape. it's needed to remove one bolt on the motor. I am going to attach some pictures that speak by themselves. However, just to mention that the "extra long arm" (it's about 160mm) helps to go above and beyond the motor body, which makes it really easy to unscrew the bolt without effort and risking to break something. I am mentioning all of these for 2 reasons - I did not have any tool to unscrew that bolt (maybe there are many and different tools for such job and people here already own the necessary tools) and while the bolt on the motor is M8, size "6" of hex key is for M10 to M12 bolts (when I look tables online). So, that makes me think the bolt on the motor is not exactly standard M8 one, if I am using hex tool size for M10-M12 bolt to unscrew, but it's perfect match. Also, i think it's good information for people that will buy just one such "hex key" for this particular task. I purchased mine in a local store for only 1.90 USD.

5) As far as I can tell all other components on the board are standard and available everywhere, e.g. resistors, capacitors, etc. So, you just need to wait the PCB to become available and buy the necessary components as any other BATC kit.
Last edited by skdi on Fri Nov 10, 2017 7:45 pm, edited 1 time in total.

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Re: DigiTwist.

Post by skdi » Fri Nov 10, 2017 7:04 pm

I don't know why, but I cannot attach more pictures to the previous post. So, here I am attaching the picture for point 5 in my previous post and want to use the opportunity to add another point:

6) for receiving the data from ISS probably the best to use would be "MiniTiouner" (if you don't know it, check BATC shop and the Wiki, as well the forum). however, since 1 year, there is open-source project that works in Linux called "leandvb":


it uses your computer CPU to demodulate DVB-S in software (it has limitations due to CPU power and USB chipset that is used), i.e. Software-Defined-Radio and the hardware needed is very very cheap USB dongle with Realtek RTL2832 chipset - such dongles are 7-10 USD shipped from China. I won't go into more details here (maybe even that's already discussed in the forum), but all those dongles differ by the RF tuner inside, as far as DVB-S is concerned, best tuner would be R820T2 and the cheapest RTL2832 + R820T2 I found on eBay is 7.90USD shipped. In any way, there are more high-end ones that use TCXO, etc. but the price there is closer (even over) "MiniTiouner". Also, I have no idea if the cheap ones would be stable enough for proper reception of DVB-S.

P.S. it seems more than 3 pictures cannot be attached to a post...in next one I will put last 2 on my pictures for point 5.
hex_arm_2.jpg (151.28 KiB) Viewed 3312 times
hex_arm.jpg (89.75 KiB) Viewed 3312 times
1_motor_bolt.jpg (265.89 KiB) Viewed 3312 times

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Re: DigiTwist.

Post by skdi » Fri Nov 10, 2017 7:05 pm

hex key size 6 with extra long arm in action...
2_motor_bolt.jpg (277 KiB) Viewed 3313 times
3_motor_bolt.jpg (98.15 KiB) Viewed 3313 times

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Re: DigiTwist.

Post by G4EWJ » Fri Nov 10, 2017 7:11 pm

I have a few blank DigiTwist pcbs available. If anybody would like one, please email your address to my callsign at yahoo dot com. A £3 donation to BATC is requested. There are currently 16 people on the mailing list, from eastern Europe to South America.

The reason for using the RT5047A was that Farnell had just started stocking it, so it should be available in Europe, USA and many places around the world. The LNBH26 is a 4x4mm, 24 pin QFN chip with pads underneath at 0.5mm spacing. Not something that I would recommend for home construction. :)

Sourcing joiner bars continues to be a problem. I didn't think it would be so difficult. As you can see, some members of the group are looking at options.

I have yet to receive the ISS using a 60cm dish. I put an analyser on the receive converter during a pass and while I could see the ISS about 10dB above noise at times, there were signals 40dB stronger coming from 3G and 4G transmitters 250m away. There was also a large signal in the 2350-2390Mhz part of the band. I need to get a good filter and try again.


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Re: DigiTwist.

Post by skdi » Fri Nov 10, 2017 7:25 pm

G4EWJ wrote:The LNBH26 is a 4x4mm, 24 pin QFN chip with pads underneath at 0.5mm spacing. Not something that I would recommend for home construction. :)
that's good point, in fact it would be kind of impossible for hand-soldering. it's actually related to another question I have - what about the author of the PCB (maybe it's you Brian), to generate and share .gtp (Top Paste) and .gko (Board Outline) GERBER files, that will allow to order stencil and make the SMD soldering lazy - I can do it by hand, no problem, but with stencil is really lazy and stencil from polyimide film are very cheap now to order. However, that's nothing important, just something good to have, but by no means required.

P.S. the DigiTwist PCB would be good for any other application when you need to provide LNB power, DiSEqC commands and 22kHz tone. So, that PCB by itself is very useful!


Re: DigiTwist.

Post by mans9h1gb » Fri Dec 01, 2017 12:01 pm

Hi Brian,
I am very interested in the project.
Managed so for to source out, convinced my brother to go IP TV, one Diseqc rotator and have a few Adruino nano.
I have a couple of alternative mounting ideas which I would like to try as soon as I have the second rotator.
I cannot seem to find the links to the complete schematic Firmware and software for the project.
Have they been published yet and is yes can you be so kind as to direct me to the link please.
Thank you in advance for any help and assistance .
Again well done and keep up the good works
Mans. 9H1GB

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