What Did You Do Today (2017)

Anything with an FTDI chip will be fine.

You don't need to spend £23

**LINK**

Neil

I didn't spend £23, I spent £46, I bought two

Bit of a landmark day today. The lad and I made the first cuts on the Myford ML7 - only about a year after it entered the workshop for a quick freshen up!

It seems the "wide guide" conversion has been well worthwhile. Even with the lathe temporarily bolted to the bench top, no levelling involved, a fine cut over a six-inch long test piece of 1" diam. steel bar revealed no measurable taper over the full 6" length. Amazing for a clapped old bed, with up to .005" wear in places. And considering the headstock bearings were scraped along the way, I would have expected at least a bit of bed twisting to be needed, if not full-on headstock realignment. Either I am the world's best bearing scraper, or incredibly lucky. I rather suspect the latter! Nonetheless, a very pleasing result. I could not, with a standard Mitutoyo micrometer, detect even what looked like a few tenths of a thou taper.

And then, banging in a centre hole and a tailstock centre, we were able to take a .100" deep cut at normal fine feed of just under four thou per revolution with no sign of chatter and keep it up for the length of the test piece. Nothing wrong with that for a small lathe. It seems quite rigid under load indeed.

Likewise, a facing test showed just under one thou concavity - just within spec, which is 0 to 1 thou concave.

Very pleasing indeed. I will write up the Wide Guide conversion "how to" for Neil now that it has been proven to work so well, saving the prohibitive cost of having the bed reground (transport costs from my location would be more than the grinding!).

Edited By Hopper on 27/11/2017 09:58:39

What's all this about -3V, -5V and -20V? Must be a whole new world of RS232 I knew nothing about?? Sounds intriguing. I'd always thought RS232 stayed within TTL levels. Could someone explain?

Murray

PS: I know most micros these days are not 5V, so lower signal level compatibility is understandable. I see the FTDI devices are compatible with signals down to 1.8V

Edited By Muzzer on 27/11/2017 10:26:27

Ah - but yours had D-connectors...

As an ML7 owner I will look forwards to reading Hoppers write up about Wide Guide conversions.

RS232 is a specification. Primarily defined in terms of signal levels.This may explain a little more.

**LINK**

If the interface doesn't meet the spec it isn't RS232.

Like many things (hoover) RS232 has come to be used in a more generic way to describe other serial links that strictly speaking aren't RS232.

regards Martin

When I first encountered it in the '70s it was +12v to -12v minimum officially on the Tx but the Rx was expected to detect at 3.6v as far as I can remember. Probably there is a proper spec somewhere to prove me wrong. The upper voltage might well have been 15v to align with lead acid batteries. Of course on short runs +/- 5v worked fine but getting a -ve was annoying. So it you were building both ends you could tweak it to work on +ve only.
The negative was essential in the original concept to allow for significant ground loops and effects of high currents in nearby machinery making the 0v rather variable.
For long runs at slow speed 20mA current loop was preferred. You either had some current or you didn't regardless of what voltage it took to drive the current through your long thin wires.

Muzzer:

RS232 was defined by the American EIA, chosen as the UN standard then modified by IBM who couldn't fit two 25 way D subs on their expansion cards. In the spec +12V is a zero and -12V is a one. RS232 through telecom twisted pair is good for 100 yards, through shielded cable, 10 feet if you don't try and up the Baud rate too far. Of course you won't get +-12V after 100 yards so the standard accepts down to +-3V. This new Chinese standard seems to be inverted TTL which is fine and dandy so long as the other end is okay with it.

My cables do indeed have D subs, they also have a spec sheet, Farnell's guarantee, next day delivery and 2 meters of length

I've come across kit that insisted on ±20V. For a while ±12V was common, more recently ±5V is widely sold as 'RS232-Compatible'. Most modern stuff is OK at 5V, but don't bet the farm on it.

RS232 has been eccentric for as long as I can remember. Loads of change and variations over the years; you can never quite trust it to be compatible. Plugs/sockets, wires used/not used, how long the cable can be, voltage levels, baud rate, stop bit length, parity, controller capabilities, software control like XON/XOFF; you name it - it can vary!

Getting RS232 to work in a mixed environment can be a trial - in the 1970's installing mini-computers, modems and dumb terminals, we read specifications carefully, worried endlessly about cables, and had an expensive protocol analyser ready for diagnosis if it still didn't work. Horrible.

USB to RS232 converters are a similar mess. Some chips don't implement the full protocol plus there are a lot of dodgy fakes about. Been a while since I bought one but as mentioned the FTDI chip is good. There's another that's OK but I can't remember what it is. I'm afraid buying expensive won't save you, see 'fake'. The safest way is to find a reputable seller and buy from them. For example, people who sell RS232 based accessories for ham-radio, astronomy, test equipment etc. will likely stock 'good' converters to go with them. Pot luck off ebay is more risky.

Dave

Well, I'd better get cracking on it then. Currently working on the preliminary article on how to measure up the bed to determine if it needs regrinding or not.

.

Essential background video from Spitting Image, here: **LINK**

https://m.youtube.com/watch?v=CDlj0jBtYmQ

MichaelG.

I used to get serial cards back blown to shards, many a happy hour spent snipping the legs off 1488's and 89's so I could remove them one at a time. I could only think that somehow they managed to connect data pins before frame ground??? I responded with a splendid card using fast Zenners to protect the pins from over voltage but I couldn't compete with the Chinese cheapies and had to move on.

Reclining armchair working again.

Re-seated all the power plugs and it sprang back into life again.

Geoff - Pulled a neck muscle drying myself after shower a week ago and still giving me what for 😤

Just got off the phone with mother. Traumatised. She's seen the christmas decorations in Keynsham...

Ah, well, you live and you learn! I've used RS232 on and off since the late 70s but only ever with micros and only ever with 0-5V or less logic levels. I'd fondly imagined that the signals on the bus were simply TTL levels and the only signals I'd looked at were presumably the TTL side of the line driver. No wonder I was perplexed!

Murray

Arm yourself with a breakout box if you want to do battle with RS232 and win.

Mike

Useful little boxes I have one on the shelf but not used it for a few years. Always good for making a quick cross-over link if did not have a cross-over cable around. Still carry RS232 cross-over cables and RJ45 cross-over cables with my laptop for on-site work. In fact my newest all singing/dancing Dell rugged laptop came with a RS232 port and a dedicated Fischer Power Port. Nor sure what I'm going to use the Fischer port for though. I've even got a self-configuring serial port adaptor somewhere.

Fun days in PC support when used to have to set up DMA and I/O ports and interrupts when added an new adaptor card to a PC. In fact I still have an IBM Model 64 hidden away. Monochrome, bugger all memory (16K IIRC) and 5.25" floppy drivers, no hard disk in those days.

Colin

Friend came round and showed me how to tram the mill table in. Learn something every day.

Phil

SpeedyBuilder5 - That shovel on the lawn tractor looks good, is it fixed totally or can it be moved up and down a bit?

Chris