For the price of one of those you can buy twenty-four ULN2003s each of which will run three solenoids, so it's 72x the price.

Well , when you put it like that, doesn't sound that good. However the majority price on our board comes from the isolation, due to logistical reasons(mainly availability, and due to its presence in our system on other boards) we go for the iso7240, pricey overkill, but does the job. Your 74HC123 idea sounds very interesting however, I'll have a look

 

@LowQCab I don't think PWM would work over here.

The valve is bi-stable with no default. It maintains the position to whatever it was last energized to

The single coil with spring return sounds perfect tbh, and we might switch to them in the next iterations, but we already have too many of these dual coil versions for now so will have to work with these

 

The big question is about the valve staying in whichever position it was in when the power switches off, such as in many machine "E-STOP" modes.

 

Powering one coil will take it to one state, powering the other will lead it to the other.

That's what I would expect, but you said it works by energising only one coil ???

 

That's what I would expect, but you said it works by energising only one coil ???

Clearly there is a failure to communicate here. "Works" is not an adequate description. If it shifts to the opposite position when one is powered, does it return when that coil is off? OR, does it WORK and shift to the opposite position with the other coil powered. I used to have this sort of problem with one purchasing person.

 

Clearly there is a failure to communicate here. "Works" is not an adequate description. If it shifts to the opposite position when one is powered, does it return when that coil is off? OR, does it WORK and shift to the opposite position with the other coil powered. I used to have this sort of problem with one purchasing person.

Here is the info sheet.
Status at Power-OFF = Self Retaining. !

(The PDF is 900 pages!)

 

OK, there is the required information, in the last two columns: Status at power off SELF RETAINING. That tells me it is two position maintained, So two drivers are required, But it could also be implemented by means of a single relay having both an NC and a N.O. contacts, connected as a form "C", so that relay active one coil is driven, relay inactive, other coil is driven. But you will need to use a long-life relay.

 

OK, there is the required information, in the last two columns: Status at power off SELF RETAINING. That tells me it is two position maintained, So two drivers are required, But it could also be implemented by means of a single relay having both an NC and a N.O. contacts, connected as a form "C", so that relay active one coil is driven, relay inactive, other coil is driven. But you will need to use a long-life relay.

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MisterBill,
this format doesn't necessarily "require" 2 Drivers,
a single FET-Driver scheme will work with any configuration,
except one that actually requires "no-Power" for a given condition.

This scheme can also double the number of available Outputs, ( if that's of any value in this situation ).
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The valve in this application is held in the last position selected by a mechanical detent, and so it will not move until the alternate coil is energized. How can only one of two coils be operated alternately by a single output, unless a scheme with a relay is used???
In addition, any sort of toggling scheme will require memory to know which position it is in. That mode is in violation of several safety rules.

 

I suppose it comes down to how the system is designed ..........
You can have a system that acts like a mechanical machine,
or, a system which electrically resets all Valves to a default position before starting, when Power returns.

Having a machine which may start-up with Valves in an unknown position, ( no default positions ),
sounds rather hazardous to me.
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