7i84D - MPG inputs & 5v encoders

I'm using 5k pots on a 7i84d analog inputs for overrides and find I don't really like them.  I thought I'd like them more than the encoders I'd used previously, but it's annoying to have Lcnc start up at 100% with the pots turned down or up and have to manually reset through the screen.

Connecting the encoders back up should be simple, but I don't have 5v up in my operator panel - field voltage is all 24v on TB2 & TB3.

Question 1 - can I attach a buck converter to my 24v rail (which feeds field voltage) and power the encoders that way?  Or even run 5v from the 7i76e's TB3 up to the encoders?

Question 2 - the encoders are the type that have a built-in NO switch.  Assuming that the 5v switch output isn't enough to trigger an input on the 7i84d... do I switch TB2 to be 5v field vin with a buck converter to be able to use the encoders and switches?

Thanks,
Ralph

The 7i76e's MPG inputs include 5 volt power for this purpose

Thanks Rod, thats what I suspected when I saw all the 5v pins on the 7i76e.  Shouldnt be too bad to pull some more wires up to the operator panel.

Any idea on how to use the encoder's built in switches? I think i need >12.5v to register the signal.

For the switches I would use field power (normally 24 v)

Here is how I did it.
forum.linuxcnc.org/show-your-stuff/32029...build?start=20#85279

Yes, using a buck converter for 5V will work.
If the switch output can only be 5V, You can power
VFIELDA with 5V and get 5V compatible inputs
on the 'A" inputs.

NOTE that 7I84Ds have an artwork error that connects VIN to VFIELDB so only
VFIELDA can be separate, from the 7I84 manual:

WARNING: 7I84D cards previous to revision A have VIN permanently connected to
VFIELDB so only VFIELDA can be run from a separate voltage. W1 is not functional
on these cards.

PCW,

I don't see a "REV A" anywhere on the 7i84D, so I'm guessing I have the older version despite buying it a couple weeks ago.

So if I connect 5v to VFIELDA and 24v to VFIELDB (mode 2), then:

TB2 INPUT16 to 19 = 5v MPG
TB2 INPUT20 to 31 = 24v inputs
TB3 INPUT00 to 03 = analog or 5v
TB3 INPUT04 to 15 = 5v

Is this correct?  If so, that means the analog inputs will need to be 0-5v instead of 0-24v, yes?

Thanks,
Ralph

rodw wrote:

For the switches I would use field power (normally 24 v)

Here is how I did it.
forum.linuxcnc.org/show-your-stuff/32029...build?start=20#85279
 


 

Thanks Rod.  Unfortunately, the NO switches are built-in to the little encoders.  You feed them with 5v and they have 3 outputs (A/B and a NO contact).  I dont think there's a graceful way to convert them to 24v output without additional components (relays, level shifters, etc).

EDIT - now that I think about it maybe that's the way to do this.  Leave VFIELDA & B alone, and hook up the encoder switches to little 5v coil relays.  That way all inputs to the 7i84d are still 24 volts, analog inputs remain 24v, and the MPG inputs trigger at 2.5v.

Hmm... this bears consideration.

Why not just use opto coupler ?

Remember the contacts of the switch may only be rated at 10ma@5v.

spumco wrote:

PCW,

I don't see a "REV A" anywhere on the 7i84D, so I'm guessing I have the older version despite buying it a couple weeks ago.

So if I connect 5v to VFIELDA and 24v to VFIELDB (mode 2), then:

TB2 INPUT16 to 19 = 5v MPG
TB2 INPUT20 to 31 = 24v inputs
TB3 INPUT00 to 03 = analog or 5v
TB3 INPUT04 to 15 = 5v

Is this correct?  If so, that means the analog inputs will need to be 0-5v instead of 0-24v, yes?

Thanks,
Ralph
 

7I84 analog inputs are always 33.6V full scale regardless of field voltage
The field voltage only changes the input thresholds (to 60% and 40%
of the field voltage)
Since the MPG needs 5V anyway, it looks like the simplest
way is to use The Field I/O "A" at 5V

ALittleOffTheRails wrote:

Why not just use opto coupler ?

Remember the contacts of the switch may only be rated at 10ma@5v.
 

 

'cause I've never used an optocoupler by itself - simply didn't occur to me.

I've got a bag of these encoders and a little 5v relay module on the way.  I'll hook them up and see if they fry trying to drive the relay coil.  If so, I'll move on to Plan B.

But I think I'm all set with the arrangement.  VFIELDA will be 5v.  Encoder switches will go to those inputs on TB3, and everythign else will go to TB2 at 24v.  24v analog to TB3 I00-I03, and MPG's to TB2 I16-I19.

All I need is to mount and wire the buck converter I've got on the bench.