Retrofitting a 1986 Maho MH400E

drimaropoylos wrote: Mesa states for the 7i84 that it can handle relays, but it doesn’t state the same for the contacts on the 7i77. They have the same current and voltage capability but it is not clear that 7i77 will handle the overvoltage during the switch of on the coils. Can the diodes on the Maho relay board protect the 7i77? Or the 7i84 (or some buffer solid state relay board) is the only way?
Nice work on the panel Mark, are you going to use 7i73 for the matrix on the panel?

The 7I77 Field I/O is the same as the 7I84. The 7I77 and 7I84 outputs can drive small relays directly
without flyback diodes though in general flyback diodes are suggested since they will reduce switching EMI
and power dissipation in the output chips.

When no flyback diode is used, the energy stored in the relays magnetic field is
dissipated in the output driver chips MOSFET at turnoff. When a flyback diode is used,
most of the stored energy is dissipated in the relay coil at turnoff.
There is a slight disadvantage of using flyback diodes for high speed operation since it will slow
the relay de-energise time slightly.

Thank you for the detailed response.

Hi John,

I decided not to get a 7i83, as I have enough spare inputs on the 7i77. I am multiplexing the control panel buttons, so only 10 inputs are used for the 24 switches. I also want to make a pendant, and think I can just squeeze everything into the existing 7i77 and 7i84 I/O.

The switches feel pretty good. The travel is about 1-2mm. There is no positive click, and the 3D printed buttons can hang up if the force is too off axis. I'll see how this works, and if they are a pain in use, I can back them up with some coil springs. The seminar hotel next to my work has pens with the idea spring in them. Our company sometimes has seminars there, so I havest the left over pens just in case. I kind of plan to CNC mill some aluminium buttoms once the MAHO is running. We'll see if that happens.

Mark

Hi, i haven’t quite understand how multiplex works on the 7I77. I thought that multiplex can be done only with 7i83 or on some Pokeys style dedicated hardware. The 7I77 card can sense short circuit between the inputs?

John

Not sure what the question is...
edit:
Oh I think I see, you mean how can you multiplex inputs?
This can be done all in hal with almost any kind of I/O device
to expand the number of inputs though diodes may be needed externally
to prevent "sneak paths"

The LinuxCNC component matrix_kb implements input muliplexing using any kind of I/O device
including parallel ports

When you press a bouton in the matrix keyboard system, a connection from one input to another is made. The 7I77 can sense a connection between inputs?