Wireless RS232 link ???

[awemawson]

I have three CNC machines all of which use relatively slow (9K6 baud) RS232 serial links to talk to the pc I use for up and down loading programs. It would be very useful to have a simple point to point wireless link to avoid trailing cables, OR maybe an RS232 to wifi coupler to perform the same task. I've been thinking of strapping an old pc to each machine and shoving a USB wifi adaptor in but that seems very cumbersome.

Commercial 'wireless DNC links' are available if you are prepared to sell your sole to buy them, but I'm not. Anyone have any experience in this field that they'd care to expand on?

[vtsteam]

Here's the first thing I found so far:

http://www.usconverters.com/index.php?main_page=product_info&cPath=70&products_id=404

[vtsteam]

Actually, that's for remote connection to a computer -- not sure if you want that Andrew.

If it's just point to point wireless RS232 then their other product is:

http://www.usconverters.com/index.php?main_page=product_info&cPath=70&products_id=186

[awemawson]

Thanks Steve - that's food for thought. I've been round this circle a few times in the past five years and still I have cables draped across the floor !

[rockknocker]

A bluetooth serial adapter looks like it might work as well. Googling "bluetooth serial adapter" results in several different options.

http://www.usconverters.com/index.php?main_page=page&id=67&chapter=0

You could also use something similar to SparkFun's serial modem modules, but they would need some circuitry at either end to level-shift and power the modules. Also, they might be a little overkill, your machines could be 1500' away! Nothing like splashing RF energy all over the countryside...

https://www.sparkfun.com/products/155

[awemawson]

Thanks Rocknocker, those look interesting. I hadn't appreciated that Bluetooth would cover 300 foot, which is more than adequate. Need to get my hand round how to handle the handshaking, as one of the controllers will only work CTS/RTS and not XOn/XOFF

[rockknocker]

The bluetooth serial adapter sold through USconverters appears to support both methods of handshaking, but there is only one way to truly find out.

http://www.usconverters.com/index.php?main_page=product_info&cPath=65&products_id=228&gclid=COTQ6a2H5bkCFSNyQgodSEgAUg

I wouldn't count on getting a full 300' out of these though, especially in a machining environment. I would recommend 100' or less and 1 non-metal wall. That advice is not based on bluetooth experience though, just general wireless experience.

[awemawson]

Yes thanks for that. I wish that the 300 foot would be a limitation, but my workshops not that big - 30 foot would probably do !

I'll ask them if they ship the to UK

[DMIOM]

Andrew,

You can also buy such packaged RF modems from the likes of Black Box, Brainboxes, CoolComponents etc. in UK.

Can I suggest one thing you might need to check though before investing too heavily in any such kit, and that is the levels that the RS232 is driven at...  "Typical" RS232 at EIA levels has a swing of +/- 12v (from memory, spec allows swing up to +/- 15v and down as low as +/- 3v) but for noise immunity in industrial environments,  industrial kit tends to have the detection thresholds set towards the upper end of the spec. However, some modern adapter gadgets (and some USB-serial adapters) can operate with the correct polarity but only swing, say +/- 5v  and/or have very modest current source/sink capabilities - and hence whilst the adapters will happily connect two PCs they won't always provide a 'loud enough' signal for an industrial CNC or PLC to recognise. 

I had a hardwired link from my drip-feed PC to a TNC155 which included an opto-isolated safety barrier - the hardwired serial had enough 'oomph' to drive it but a BT one didn't. On the bench, I found that the BT units were only driving +/- 4.7v off load and +/- 4.3v into the opto whereas that hardwired ones could strill drive +/- 11.5 into the opto.  In that case I was able to bypass the optical barrier as the wireless link removed any possible fault path or ground loop issues.

Dave

[awemawson]

Dave yes thanks for your input.

I've been doing a bit more reading today. As you say the are quite a few modules, both Bluetooth and WIFI that are available in the UK that are intended to be 'built in' so are bare boards but quite cheap. Most are actually operating at TTL levels and would need a 75188/89 level converter or equivalent. I say TTL levels - how they manage that when they operate off 3.3v is a bit of a mystery !

I'm rather coming to the conclusion that it's a lot of faffing about and I'd do better perhaps to knuckle down and put in a proper wiring scheme. At least that would ensure better noise immunity.

What started this train of thought was my Beaver Partsmaster. The RS232 socket for DNC is on the side of the console box housing the operator panel and monitor for the TNC355 control. However this console box is mounted on a long swinging arm so any cable has to go back to the pivot point then vertically up. However above the pivot there are no roof trusses to fix anything to for perhaps 12 foot making draping wires a right royal pain! Hence thinking wireless! At a push I could re-wire the Heidenhain RS232 port so it exits within the main electrical enclosure rather than the console which would at least get it nearish to a wall!

[DMIOM]

hi Andrew,

regret I can't help with the sky-hook !

I must admit I would be a little reticent in routing the serial cable via the power cabinet, as I would be concerned over increasing proximity to kit with sharp power edges / PWM can splurge RFI; especially if you're drip-feeding.

If you decided to go the 'bare board' route, the likes of a MAX3232 is a 3v version of the old MAX232 which will operate between 3v and 5.5v for power & logic.

Dave

[awemawson]

Dave,

The box containing the TNC355 is in a separated compartment from the (mega)power electronics so I think it'd be ok. Heidenhain are extremely good at specifying screening and earthing for their controllers as you probably know from your TNC155. The installation manual goes into minute detail!

Andrew

[DMIOM]

....At a push I could re-wire the Heidenhain RS232 port so it exits within the main electrical enclosure rather than the console which would at least get it nearish to a wall!

Sorry Andrew if i misunderstood - twas just the 'main electrical enclosure' reference that worried me

Dave

[awemawson]

Dave, it was my bad explanation. I've added a picture a bit further up the thread to show the issue. Picture is of before I bought it so it's still at Bristol University.

Andrew