Invert the output from an opto switch

[uspl]

Howdy all

The router build is coming along well, cold weather means I am indoors doing fiddly things instead of the shed so the opto home switches are on the agenda.

I am using the circuit as per http://www.cnczone.com/forums/genera..._switches.html and many other threads and have the LED flicking off and on just fine.

My issue is, how do I get this to work as ON when the opto is clear, i.e. not blocked. I want to use the switches as NC so that a power failure or cable fault on the opto circuit will cause an alert on Mach3.

Thanks for any suggestions

David

[doorknob]

Can't you reverse the 'sense' of the input by switching the Mach3 input signal definition from Active Low to Active High (or vice versa)?

[uspl]

Can't you reverse the 'sense' of the input by switching the Mach3 input signal definition from Active Low to Active High (or vice versa)?

Yeah I can but if the power fails on that circuit or some other fault occurs, Mach3 wont see it.

[doorknob]

There are several variations on the circuit described in that thread - do you have a diagram of how you actually have it wired?

[Al_The_Man]

You must have the 'Operate on Dark' version instead of the normal 'Operate on Light' type.
The latter is the fail safe version you are looking for, which are normally ON when un-blocked.
You could use a 2N7000 with pull up resistor on the gate to invert the output, use the same power source as the opto.
Al.

[uspl]

Thanks Al

The opto is the ZD1901 from Jaycar here on Oz, http://www.jaycar.com.au/products_uploaded/ZD1901.pdf

Wiring is like the pic attached.

Could I trouble you to expand on the wiring for the FET, my electronics sort of stops about "First, turn on the soldering iron....."

I have a few solid state relays I could use instead but it seems silly to use an $8.00 component when a $0.60 one would do the same job.

[Al_The_Man]

Looks to me like you have it connected wrong? No1 the device is already operate on light so you don't really need the inversion for safety reasons?
If you put the LED in series with the collector instead of parallel it will switch but indicate when non-triggered, i.e. switch off when blocked.
If this is an issue, and you want the inversion, the 2n7000 source pin connects to the emitter, the collector to the gate, and the drain pin would be the output, if you want to invert the LED indication then put it in series with the 2n7000 drain pin and whatever you are switching into if this is a BOB, if going into a P.P. then also use a 1k resistor on the drain to +5v and replace the gate 1k with a 10k.
Al.

[uspl]

Hi

By "wrong" do you mean Collector and Emitter reversed ? I thought so too based on the other CNC Zone post but when i looked at figNoggle Designs: Photodarlington Optical Interrupter Switch Wiring How-To I wired mine the same way and got the result of blocked=LED On.

Any chance you sketch what you think the wiring should be, I can test it this afternoon and report back. This particular opto is the one of choice for many of us in Oz as it is pretty much all you can get in the market at the retail level.

Cheers

[Al_The_Man]

By wrong, I meant you could have wired the LED in series with the collector, just that it will light on non. shuttered (off), I can whip up a dwg to include the 2n7000
Al.

[uspl]

I can whip up a dwg to include the 2n7000
Al.

That would be very generous of you, thanks

[Al_The_Man]

Something like this maybe, but I don't see why you need the inversion?
Al.

[uspl]

Thanks Al, I will drop by the local parts store and grab some trannies tonight.
My opto must be the operate on dark type, as measured with the multimeter I get 0v at normal state and 4.99v against a Vi of 5.00 when I block the slot.

Weired

Thanks again for the schematics