Boxford TCL125. (Fresh start )

[inee]

https://www.ebay.co.uk/itm/RS-Infrar...4AAOSwFIVe2WWG

[John11668]

Will try to snag a couple of those inee

[John11668]

Ahh doddy !
So simple and straight forward. How could I possibly get it wrong?

So our friends at Boxford chose a 10v output without any apparent resistor in series? or where did they hide it
And I guess I will have to use 12v so maybe will have to add a resistor, or maybe 5v but I will need to go back to my 1968 physics A level notes if I really want to understand your calc .

I can manage most mechanical stuff , and have a reasonable grasp of electrical machines , single and 3 phase, Even managed to get a handle on electronics in the days of thermionic valves , but I have to say that when the world turned upside down, when the time came when current stopped flowing from positive to negative and it was decided instead that current was a stream of negatively charged particles careering towards a positively charged source then that was the time at which my "electronic "head started to hurt .

What I am saying is you have to bear with me a bit while this stuff sinks in . When I get my new switches, I may need to come back with the spec, and ask you to turn forward voltage and forward current into a suitable source voltage / resistor combination.
Hope you haven't got too sick of me by that time

[John11668]

OK so I have ordered new switches and in the meantime had a closer look at these





So this might be surprising but looks like Boxford have chosen to wire these lamps like xmas tree lamps ie in series .
So our green supply wire seems to ring around the switch commons then on to the two lamps in series. How do I add the forward voltages in this configuration??

Now as Inee points out from the Boxford wiring diagram the input voltage is 10v and there is no sign of a resistor . Is it possible that the lamp resistances stack up so that no external resistor is needed . and how would that be affected if i chose to supply 12v?

[Doddy]

Hmmm, you previously linked a reflective opto-coupler, (EDIT: Ah, I see what you did there - the linked datasheet has the slotted version later in the document) these are slotted opto-couplers (same premise, just a different physical configuration) - these more common with slotted wheels as shaft-encoders, etc.

For LEDs which typically outlive the service life of the machine, wiring in series is perfectly fine, and common practice. As you probably guess, you just need to add the forward voltage drop across the individual LEDs into the standard calculation for series resistor (the advantage being that you only need one resistor).

Where this conversation doesn't need to go, but I'll mention anyway, the forward voltage drop is not absolute - it'll vary across devices, temperature, forward current, day-of-the-week, and if you look at it funny. What that means is, you always design (calculate the series resistor) based on nominal values - and the slight variances fall by the wayside... what you can't do is drive an Led without a series resistor of some sort (or rather, a current limiting device or circuit) - as any slight variance in the forward voltage drop would have a significant swing on the forward current and could result in the destruction of the LED.

So, given a wet finger of 1.8V Vf for an IR LED, at 12V drive voltage and an If of 10mA, you'd end up with a series resistor value or 840 Ohm, or closest value of 820 Ohm in the E12 range of resistor values. But, you're overthinking things a little - you can wet-finger resistor values given a safe working forward current. So, whether it's one or two LEDs, and 10V or 12V, you'd probably just pick the ubiquitous 1k resistor. It's close enough. There's plenty of other factors in the system that will impact the performance more than 10-20% accuracy of resistor values.

I'm convinced to within a gnat's arse that there will be some method of current limiting/control in the Boxford board, regardless of the schematics. It's the done thing. And the cheapest (and most reliable) method is a series resistor. It *could* be that the original opto-isolators had integral series resistors for 5V operation (after all, once upon a time 5V was common logic supply voltage), but it's almost irrelevant here - you know the opto's you're buying, you can find the datasheet, you can determine the Vf, and then you can determine the series resistor. But 1k will do.

Your schematic is functionally okay, but remember both the LED and the associated photo-transistor are polarised devices - you need to get the wiring the right way around.

[JAZZCNC]

John if your thinking to go with Linux CNC then I would plan for it now because Mach3 can only use a Single index pulse or slot for the spindle encoder, Linux CNC can use multi-count encoder and will give you much better speed control.

[depronman]

Just adding to Jasscnc reply. You will never get mach3 to thread correctly and reliably (been there got the tee shirt, cap and video)
The single pulse per rev is just not enough resolution to cut a thread
This was the one compelling reason that I changed to linuxcnc
Linuxcnc cut a thread on the first attempt and as done ever since The only failure I have had was when I tried to increase spindle speed beyond what the lathe could cope with in terms of accelerating the Z axis and decelerating it
I have a job that needs a M10 x 1.5 cutting on the end of an aluminium bolt. I thread at S500 in 10 passes with two spring passes fine every time.
The stability of linuxcnc over Mach3 is a very welcome bonus. Linuxcnc as never screwed up on a run of parts, I cannot say the same for mach3

now the setup of the two is a different matter all together. But a basic lathe setup can be done with the step and config wizard and is perfectly usable

Paul

[John11668]

I plan to go there Jazz, but have been working with Mach which I am moderately familiar with . Waiting the switches to give me spindle speed measurement and prove to myself I have a working machine . I have an E stop but need to reinstate interlocks and z traverse limit. Has been a steep learning curve but I would rather go a step at a time and Iinux will be one of those future steps.

[John11668]

I accept what you are saying too Paul .
I just feel I need to get it doing some plain turning first in mach . Will go to linux before I attempt any serious threading.
My target is to do a few shouldered bolts for vintage motorbikes . Linux probably has to be part of that project.

[depronman]

Get it running on mach3 then but forget about the spindle speed feedback altogether until you jump to linuxcnc
It will not thread in mach3 so other than getting a spindle speed readout there is no point

Paul