Designing an I/O protector

[ADWSystems]

I would like to design, or see if it is feasible to design, a module (eg., small PCB) I can reuse that will protect the inputs/outputs of a microcontroller or other logic level chip. I am work with many multi-voltage designs and would like to create, if possible, a module I can build multiple of to protect the logic circuits.

I am thinking the heart would be a CEL PS2501-4 optoisolator. It seems to have one of the highest CTRs, can handle a wide range of diode If (abs max 80mA with best CTR in the 5-10mA range), and an OK transistor Ic (50mA).

Here is what I have for design requirements:
1) Cheap
2) Small (size and component count)
3) Optically isolated
4) Reversible. I would like to be able to use the same board to protect the logic chip inputs as well as it's output by just turning the board around.
5) 4 channels on the board, matches the 4 optos available in the PS2501.
6) Diode input to handle at least 5V-12V inputs
6a) It would be even better if the input diode could accept at 3.3VDC
6b) It would be great if the input diode could handle 24VDC. I think this is a long shot without a clever idea. If diode resistor is 1k, then the power is just over 1/2W. That would be a lot of big resistors on a little PCB

I'm sure I missed some requirements that we will discover as we go along.

 

[KeepItSimpleStupid]

Take a look here (bourns TBU): https://www.bourns.com/productline.aspx?name=tbu

and the Analog Ddvices iCoupler stuff.

 

[ADWSystems]

Transients and the like are not the problem I'm worried about. I'm looking to protect the controller/logic from me, from wiring errors. Looking at the projects ahead, I have 5V, 12V, and 24V digital signals. Plus there are relays to read (inputs) and write (outputs), and better yet, the relays are not all 5V, some are 24V. I suppose a better title might have been "Reversible Universal Level I/O Shifter".

My grandiose target would be to create a circuit that can have a 3.3-24V input from a controller and level shift to an output of 3.3-24V. The highest load on the output would be driving a relay directly.

P.S. If 24V input on board is not obtainable, then 12V as a minimum with a method to drop 24V to 12V off the board.

 

[KeepItSimpleStupid]

So, the signals are "slow". The https://www.linear.com/product/LT3092 current source combined with an optocoupler. The LT part does work at 1.2 V. That might do the input side of things.

Why not use I/O modules besides cost?

 

[ADWSystems]

Current source. An interesting solution for the 12V and, especially, the 24V input signals. Just set the output to 7.5mA give or take and move on.

I was thinking of using a transistor array in the output, and modifying this circuit to https://www.sparkfun.com/datasheets/BreakoutBoards/Optoisolator-v12.pdf. This circuit maintains signal polarity, hi V in = hi V out. Just need to figure out how to turn on the relay on hi V in while also being able to maintain the signal polarity. Those two concepts seem at odds to me for the moment.

This is the part of circuit design that bugs me. The fact of knowing or being able to find a solution in one or a few components. What type of I/O module are you speaking of?

 

[KeepItSimpleStupid]

I/O modules: www.grayhill.com/products/io-modules-and-racks/

Basically an industrial standard at probably $20+ per point. They generally fit into a rack and a ribbon connects to the uC.

All sorts are available. Whatever in TTL out. TTL in whatever out.

For I2C look up BUSIO at gravitec.com. Uses open frame type modules (PCB).

I'll look at your pdf later.