Lynx Astro USB EQ Direct Cable

[Jim Franklin]

I have one of these cables that I have used in the past when sat local to the scopes - its about 4m long - I have tried to use a Cat 5E cable to extend the distance from the scope to my PC but it gives a communication error in the control software - normally Synscan Pro, but also Stellarium and couple I have trialed to see if they work. 

Is there a cable that will extend the Lynx cable without communication errors - or do I need one of the older "cross over" type network cables - I have tested the network cable with a network tester - it works flawlessly. 

Thanks

[Tomatobro]

I used an active USB extension cable such as one of these from Kenable

VZTEC USB 2.0 Active Repeater Male to Female Extension Cable 20m
Its been a while since I used my 6-r mount but I don't recall any issues using it.

 

[symmetal]

A standard cat-5 network cable should be fine between the scope and the EQ Direct cable, no crossover required. Just need an RJ45 coupler to join the cables together.

Alan

[Jim Franklin]

1 hour ago, symmetal said:

A standard cat-5 network cable should be fine between the scope and the EQ Direct cable, no crossover required. Just need an RJ45 coupler to join the cables together.

Alan

Odd, that was what I was using and it didn't like it...maybe its too long - 30m?

[symmetal]

33 minutes ago, Jim Franklin said:

Odd, that was what I was using and it didn't like it...maybe its too long - 30m?

RS-232 signals at 9600 baud should be good up to 100m. The EQ Direct cable uses a 5V version of RS-232 rather than +/-12V  so effective length may be reduced a little, but I would have thought 30m would be OK. Have you got a shorter cable to try?

It's possible the scope end doesn't have the same line driving capability as the EQ Direct module, and the cable inductance/capacitance is loading it too much.

Alan

[malc-c]

30m is beyond the max  workable distance for 5v TTL signals, and that  would be using a decent shielded cable.

Several things effect the quality of the data signals.  The capacitance of the cable, having a balanced cable for TX and RX,  and noise.   A unshielded twisted pair category 5 cable has a maximum capacitance of 55pF per metre, so  a  cat 5 cable can be safely used at 9600 bps for distances of around 45m , however that would be for normal RS232 standards which operates at +/- 12v, thus providing a 24 volt differential (with the dead spot of +/- 3v in the middle). 

TTL level serial/UART  only has a 0 to +5v swing, and when combined with high capacitance of an unshielded CAT 5 cable,  which effects the voltage levels making the receiving side harder to detect the swing in voltage (called rounding off and changing the wave form form a square wave to a sine), plus poor shielding making the cable susceptible to interference,  the signals  become unrecognised.  I would estimate that at 5v and 9600 bps, you could probably do 50 feet/15 meters on generic UTP Cat 5 if your lucky. 

If you have such a large distance to cover then I would suggest looking at using a wifi dongle set up as an access point and connect to it via a wi-fi enabled computer.  Alternatively use a small NUC type computer (or raspberry pi) at the mount eith a short 2 or 3m EQDIR cable, and hook that up to you home network and then remote desktop into it from your main PC.

[Jim Franklin]

@malc-c Epic - Sadly Wi-Fi doesn't work in our garden for some insane reason I have never found the source of, I suspect one of my neighbours has a jammer of some type in operation.  I think I will use a small computer to do the link - somewhere buried I have a mini-pc left over from a project - it has a POE Cat 6 port on it for power so I think that will be a perfect solution - I simply need to empty the myriad boxes in the garage to find it!!

[Jim Franklin]

On 28/08/2024 at 18:24, symmetal said:

A standard cat-5 network cable should be fine between the scope and the EQ Direct cable, no crossover required. Just need an RJ45 coupler to join the cables together.

Alan

Foound the problem - the cable was fine - it was the coupler that turned out to be faulty - bought a new Cat 6 one and it worked perfectly...Thanks

[symmetal]

That's good to hear. At 30m long too. 🙂

Alan