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Opto-isolator over fibre optics.

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Diver300

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I've connected a heat pump (one of these:- https://www.poolex.fr/en/produit/swimming-pool-heat-pump-poolex-nano-turbo-3kw ) to a hot tub (the circulation pump is one of these:- https://www.lay-z-spa.co.uk/2021-airjet-plus-pump.html)

It's working fine but there is no electrical connection between the two. The heat pump turns off if the circulation pump stops, as the water stops flowing and the flow switch in the heat pump detects that.

I won't want to use the 2 kW resistive heater in the circulation pump, but it would be nice to have all the controls on the circulation pump.

The 2 kW resistive heater is 230 V, and it would be easy enough to disconnect that and use whether or not that is being powered to control the heat pump.

The flow switch on the heat pump is a reed switch, powered at 5 V and with about 1 mA flowing through it when it's on. If that is interrupted, the heat pump shuts down, and restarts when it is connected again.

It would be very simple to have a relay, or opto-coupler or something turned on by the 230 V, with the output in series with the flow switch. That would allow the whole lot to work as before, with the circulation pump, and it's WiFi interface, all working is intended.

However, I would much rather not have electrical connections outside of the circulation pump or the heat pump, as there is lots of water around, and the controls are operated by people in the water.

Is there a way of having an opto-isolator with a fibre optic connection between the emitter and the photo-transistor?
 
I'd think the simplest is some Toslink fibre modules and a toslink (digital audio) optical cable.



The toslink interface modules have got rather pricey over the last couple of years, but there are plenty of cheap gadgets on ebay with those or similar in.
eg.


They generally have three terminals for 5V power, ground and logic in or out.
Plus some have an extra pin for a current setting resistor or decoupling cap.

Plug the fibre cable in and you should effectively have a remote 5V switch.
 
rjenkinsgb said:
I'd think the simplest is some Toslink fibre modules and a toslink (digital audio) optical cable.



The toslink interface modules have got rather pricey over the last couple of years, but there are plenty of cheap gadgets on ebay with those or similar in.
eg.


They generally have three terminals for 5V power, ground and logic in or out.
Plus some have an extra pin for a current setting resistor or decoupling cap.

Plug the fibre cable in and you should effectively have a remote 5V switch.
Click to expand...

Yes, it used to make me laugh, people wanting to use optical rather than coaxial digital, because 'optical is better' - yet it's simply an LED connected across the coaxial digital output. The same at the other end, except it's a photo-transistor.

Good call on buying cheap Ebay items and ripping them out, good money saver.
 
I found this:- https://uk.farnell.com/cliff-electr...08r/optical-receiver-conn-r-a-jack/dp/2991612 which seems to be the sort of receiver needed. Is that correct?

I've also got the board from an old Sky receiver, which has an optical output. It appears to be a simple red LED, and it lights up, so I might use that as the transmitter.

At the receiver end, I've got to find if I can get 5 V from the existing controller as I don't want to have to include an additional power supply.
 
That looks to be OK.
Good find, the Toshiba ones have gone from about £2 to around £10 or more in the last few years.
 
Diver300 said:
I found this:- https://uk.farnell.com/cliff-electr...08r/optical-receiver-conn-r-a-jack/dp/2991612 which seems to be the sort of receiver needed. Is that correct?

I've also got the board from an old Sky receiver, which has an optical output. It appears to be a simple red LED, and it lights up, so I might use that as the transmitter.

At the receiver end, I've got to find if I can get 5 V from the existing controller as I don't want to have to include an additional power supply.
Click to expand...

Once you've got the parts, try powering from an external 5V PSU, and monitor the current it takes (which should be pretty low), try it with the photo-transistor illuminated and not, and see how it varies. Then check what's available in the controller, if it's less than 5V then try dropping the external PSU down to that level, and check it still works OK. If the only available supply is higher than 5V, then calculate a resistor to drop the difference (based on the previous current measurements), it would be a good idea to place a capacitor across the receiver module as well.

The datasheet of the one you posted the link to says it works from 3V to over 5V, so all should be fine, and I would expect it to be.
 
I'm not sure if any voltage is available from the control module. I only measured across the flow switch pins, which was 5 V when open circuit and the current was 1 mA when shorted. I didn't measure what the voltages were with respect to the ground connection, or any of the other connections.


1657357450427.png


The "PCB" is the controller, the front of which has the buttons and the display. The 5 numbered connectors are clearly mains. I don't know if the temperature and flow connections are isolated from the mains, and I don't know if I can get 5 V from any of those connection.

I may need to take the controller from the heat pump and examine it more closely.
 
As you don't need high speed communication you may get away with using a normal LED and photo transistor.
I did an experiment using a 2 meter length of audio fiber optic cable. I used a white LED as a source and a L-53P3C (IR photo transistor.). With a 5 volt supply and a 1K resistor in series with the photo transistor I got about 1.7 volts across the 1K resistor. While looking for a photo transistor for visible light I found a small LDR (About 3 mm Dia.) Using the LDR I got about 2.5 volts across the 1 K resistor. That may be enough for you controller to see it as a closed contact. I did not try using an IR light source. I think it may be worth doing some experiments along these lines.

Les.
 
Nigel,
My reply was just a suggestion to get round the need for a 5 volt supply for the TOSLINK receiver.
Chris,
Most slotted opto sensors use IR light. As TOSLINK uses red visible light the attenuation of TOSLINK fiber may be too high in the IR range.

Les.
 
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