Q: 24V Line driver IC

[JohnHaine]

The SN754410 suggested above is compatible with low level CMOS voltages so should be ok with a modern pp. It also I think has in effect a Schmidt trigger input. I notice from the data sheet that it's going obsolete though RS have them in stock at about £1.40 each. It only does one way though, for 24v to pp I'd just use a single npn transistor with the 24v on the base through about 100k and a 4k7 pull-up to the pp Vcc in the collector. Remember it will invert the logic level.

[fabhund]

The SN754410 suggested above is compatible with low level CMOS voltages so should be ok with a modern pp. It also I think has in effect a Schmidt trigger input. I notice from the data sheet that it's going obsolete though RS have them in stock at about £1.40 each. It only does one way though, for 24v to pp I'd just use a single npn transistor with the 24v on the base through about 100k and a 4k7 pull-up to the pp Vcc in the collector. Remember it will invert the logic level.

Thanks for all the posts.

Case is that I already has a semi-working controlcabinet. A wood router based on stepmotors, controlled via puls/step from an ESS smoothstepper.

However I have a lot of noise (Due to improper shielding, and poor worksmanship, I know !)

Now I want to make it more correct and one of the things is to drive the stepper controller inputs (Optocouplers) from a line driver, using a shielded twisted pair cable.
Right now it's single ended connection (Common anode) and a straight, non shileded cable.

So from the ESS output, I want a Differential/Complementary Line driver, so 2 wires to each input.
In order to make it as immune as possible i want that to have 24V on the lines.
And the driver must be able to source/sink 20mA for the Photo-LED

I expect a min. of 500kHz pulse frequency.


For Limit switched i use Omron proximity sensors that work in 12-24VDC range. And is Sinking current (Ground) when activated.
Again this I want to drive in 2 wires as before, to a "reciever" chaninge the 24V line signal to the ESS input pin.

I have 5-12-24-48V available in my cabinet.

On top of the all the cable routing must be reworked, so stepper, sensor and spindle cables are routed separately.

Hope this draws a more clear picture of what I'm trying to achieve here.
Again thanks for all the replies, I have something to google now :-)

-Bo-

[m_c]

If you are going for differential pairs, then I wouldn't worry too much about what voltage the differential pair is running at. 5V is prefectly good for differential systems, as that's voltage what most modern CNC encoders operate at.
The key feature of differential pairs, is any noise that gets picked up, should be cancelled out by it affecting both wires by a similar amount and the differential voltage remaining reasonably constant. (This is a very basic explanation, which I'm sure Jonathon will criticise me for it!)
.
If you're running single ended, then yes, a higher voltage is better, which is why industrial machines nearly always run 24V control systems.

[Jonathan]

The key feature of differential pairs, is any noise that gets picked up, should be cancelled out by it affecting both wires by a similar amount and the differential voltage remaining reasonably constant. (This is a very basic explanation, which I'm sure Jonathon will criticise me for it!)

It's a very basic concept, so your explanation is good :)

There are plenty of differential driver ICs to choose from, I used these (specifically MAX490) in my servo motor drive and they would likely be fine for the application at hand:

http://www.maximintegrated.com/en/da...ex.mvp/id/1111

[Robin Hewitt]

If you are using opto couplers then your signal is current not voltage dependant and you are effectively proof against electrical interference.

If it isn't working you are barking up the wrong tree if you think screening and more volts is going to help.

[fabhund]

If you are using opto couplers then your signal is current not voltage dependant and you are effectively proof against electrical interference.

If it isn't working you are barking up the wrong tree if you think screening and more volts is going to help.

Guess I didn't pay too much attention to the cabling, screening etc. Fact is that I get faulty signals from endstops if I run them at 5V without opto. Now I changed that to 24V proximity sensors and an opto near the BOB to ground the input pin. Now that's working.

So the stepper drivers 5V opto inputs Enable/Pulse/Direction. Those are wired single ended with common anode.
Just figured to go all in and use Line drivers where I can, and make it as stable a possible.

The MAX490 chip looks perfect, if I read the specs. right. Then it can drive an opto directly (20mA) ?

Thanks again, Bo Andersen.