From Newsgroup: comp.sys.raspberry-pi

Hi - I'm working on a model railway project using pico boards, but have spotted something that ought to be improved.

The power to each section of track is scheduled to be switched by a
relay. I've a bank of 8 traditional relays, but have just realized the
total relay current will be up to a half amp or so worst case. I'm
looking to a solid state solution.

The relays are switching DC at 12V, but the polarity is determined
before the on/off relay. Most SS relays I've seen are triac-based for AC
only; one type would do DC, but not with the polarity changing (and at
10x the cost anyway!).

Does anyone know anything solid state that might do this without
breaking the bank?

Thanks.
--
Mike Scott
Harlow, England

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From Newsgroup: comp.sys.raspberry-pi

Mike Scott wrote:

The relays are switching DC at 12V, but the polarity is determined
before the on/off relay. Most SS relays I've seen are triac-based for AC only; one type would do DC, but not with the polarity changing (and at
10x the cost anyway!).

You could use a H-bridge, rather than build it from discrete
transistors/FETs they come as a single or dual bridge in an IC, possibly
with built-in snubber network.
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On 01/08/2025 09:45, Mike Scott wrote:

Hi - I'm working on a model railway project using pico boards, but have spotted something that ought to be improved.

The power to each section of track is scheduled to be switched by a
relay. I've a bank of 8 traditional relays, but have just realized the
total relay current will be up to a half amp or so worst case. I'm
looking to a solid state solution.

The relays are switching DC at 12V, but the polarity is determined
before the on/off relay. Most SS relays I've seen are triac-based for AC only; one type would do DC, but not with the polarity changing (and at
10x the cost anyway!).

Does anyone know anything solid state that might do this without
breaking the bank?

Thanks.

Absolutely

What you need is a switching MOSFET. And a couple of resistors to
control the gate and maybe a diode to absorb spikes.

I am using LB8721s.

Ground the gate to negative with 150k and feed it from your Pi with
something like 150 ohms. and connect the source to negative and the
drain becomes the switched negative output. You may want to put a 1N5187
diode across the load to calm any switch off spikes .

On a bit of metal to absorb heat these will do about 20A continuous -
they have very low 'ON' resistance so they don't get too hot.

These are only single pole and only able to switch the negative of course.

If you want to switch the positive (as well) you will need a P channel
device and I don't know what to recommend
--
It’s easier to fool people than to convince them that they have been fooled. Mark Twain



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On 01/08/2025 10:24, Andy Burns wrote:

Mike Scott wrote:

The relays are switching DC at 12V, but the polarity is determined
before the on/off relay. Most SS relays I've seen are triac-based for
AC only; one type would do DC, but not with the polarity changing (and
at 10x the cost anyway!).

You could use a H-bridge, rather than build it from discrete transistors/FETs they come as a single or dual bridge in an IC, possibly with built-in snubber network.

Good thought. If you want to *reverse* the voltage .
I am not familiar with how todays model railways actually work. I
thought they had electronics in them to control speed and direction.

Actually re reading the question he wants a *polarity neutral* switch.

That is not easy. And is not exactly what an H bridge will do.

I'd probably use a P channell and N channel MOSFET in parallel

But realistically I'd probably use a 3.3 or 5V Songle relay. They are
uber cheap in bulk from Aliexpress.

https://www.aliexpress.com/item/1005007479514478.html
Come on a board with a nice opto isolated input.
If you want full isolation just use two :-)

I use this sort of relay in my central heating controller to switch the zones.

If you want single relays then they are less than 50p in bulk.

https://www.aliexpress.com/item/1005008952307113.html

And in fact cheaper elsewhere.

The 5V coils are around 70ohms which was too low for my application
direct from a PI so I added transistor buffering - the relays draw
about 70mA

This is the sort of thing its not hard to design and get PCBs made up
for at minimal cost.
I use old style components as my eyesight is not good enough for surface
mount goodies.
--
“when things get difficult you just have to lie”

― Jean Claud Jüncker

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From Newsgroup: comp.sys.raspberry-pi

The Natural Philosopher <tnp@invalid.invalid> wrote:

Actually re reading the question he wants a *polarity neutral* switch.

That is not easy. And is not exactly what an H bridge will do.

I was wondering about using back to back IGBTs. See 'four quadrant
switching' on p23 here: https://ieee.li/pdf/introduction_to_power_electronics/chapter_04.pdf

but with IGBTs not bipolar (NPN/PNP) transistors.

Never actually used an IGBT for real so not sure how 'small scale' they can
go, but I'm seeing 6.5A versions so they're not just for kiloamp-scale locomotives: https://uk.farnell.com/infineon/ikd03n60rfatma1/transistor-igbt-600v-6-5a-to-252/dp/3585350

But realistically I'd probably use a 3.3 or 5V Songle relay. They are
uber cheap in bulk from Aliexpress.

Agreed, I think that's the simplest solution here.

Theo
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In message <106hurs$9ibr$1@dont-email.me>
Mike Scott <usenet.16@scottsonline.org.uk.invalid> wrote:

Hi - I'm working on a model railway project using pico boards, but have spotted something that ought to be improved.

The power to each section of track is scheduled to be switched by a relay. I've a bank of 8 traditional relays, but have just realized the total
relay current will be up to a half amp or so worst case. I'm looking to a solid state solution.

The relays are switching DC at 12V, but the polarity is determined before the on/off relay. Most SS relays I've seen are triac-based for AC only;
one type would do DC, but not with the polarity changing (and at 10x the cost anyway!).

Does anyone know anything solid state that might do this without breaking the bank?

There are various solutions, each with its own advantages and disadvantages.

One is to use two MOSFETS with the sources and drains parallelled, the
switched path being that between the two drains. You'll see a drop of
about 0.6V across it when it's on. (If this is a problem you can connect
a Schottky diode in parallel with each MOSFET, which will reduce the drop
to nearer 0.3V.) The principal snag is that the control voltage, which
is applied between gates and sources, has to float.

If you can drive relays momentarily but not continuously, consider
bistable relays.

David
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From Newsgroup: comp.sys.raspberry-pi

In message <106i37k$a3kn$3@dont-email.me>, The Natural Philosopher <tnp@invalid.invalid> writes

On 01/08/2025 10:24, Andy Burns wrote:

Mike Scott wrote:

The relays are switching DC at 12V, but the polarity is determined >>>before the on/off relay. Most SS relays I've seen are triac-based for
AC only; one type would do DC, but not with the polarity changing
(and at 10x the cost anyway!).

You could use a H-bridge, rather than build it from discrete >>transistors/FETs they come as a single or dual bridge in an IC,
possibly with built-in snubber network.

I am not familiar with how todays model railways actually work. I
thought they had electronics in them to control speed and direction.

Some people are still using the traditional DC systems, others use DCC,
which requires electronics in each loco.

Adrian
--
To Reply :
replace "bulleid" with "adrian" - all mail to bulleid is rejected
Sorry for the rigmarole, If I want spam, I'll go to the shops
Every time someone says "I don't believe in trolls", another one dies.
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From Newsgroup: comp.sys.raspberry-pi

Mike,

The power to each section of track is scheduled to be switched by a relay. ... I'm looking to a solid state solution.

Carefull there : any kind of sparking (like can happen with a bad contact between the loc and the rails) could cause quite a power spike on the solid-state relais and destroy it. I would suggest keeping the relais you now have.

Does anyone know anything solid state that might do this without breaking the bank?

Use Andys' suggestion*. Just make sure the snubbing network is upto the
task.

* Take a look at the H- or T-bridges used for stepper motors.

Regards,
Rudy Wieser


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On 01/08/2025 15:00, Adrian wrote:

.....

I am not familiar with how todays model railways actually work. I
thought they had electronics in them to control speed and direction.

Some people are still using the traditional DC systems, others use DCC, which requires electronics in each loco.

plus ££££££


I was trying to get something simple done on the cheap. The expense of
DCC would barely be justifiable.
--
Mike Scott
Harlow, England
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From Newsgroup: comp.sys.raspberry-pi

On 01/08/2025 14:49, David Higton wrote:

If you can drive relays momentarily but not continuously, consider
bistable relays.

I do have some, bought for another part of the project. But at IIRC ~£7
a pop, they're not cheap: I need 8.
--
Mike Scott
Harlow, England
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From Newsgroup: comp.sys.raspberry-pi

On 01/08/2025 12:51, Theo wrote:

But realistically I'd probably use a 3.3 or 5V Songle relay. They are
uber cheap in bulk from Aliexpress.

Agreed, I think that's the simplest solution here.

I'm beginning to agree. I've been hunting round for prebuilt modules to
do the trick, and nothing provides isolation like a good old-fashioned
relay. Maybe I just have to put up with the current drain.

Many thanks to all who've responded with ideas. I'll look around a bit
more, then press on with the relay bank.
--
Mike Scott
Harlow, England
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From Newsgroup: comp.sys.raspberry-pi

On 01/08/2025 17:44, Mike Scott wrote:

On 01/08/2025 15:00, Adrian wrote:

.....

I am not familiar with how todays model railways actually work. I
thought they had electronics in them to control speed and direction.

Some people are still using the traditional DC systems, others use
DCC, which requires electronics in each loco.

plus ££££££

I was trying to get something simple done on the cheap. The expense of
DCC would barely be justifiable.

A 20p transistor driving a 40p relay is probably best then
--
If you tell a lie big enough and keep repeating it, people will
eventually come to believe it. The lie can be maintained only for such
time as the State can shield the people from the political, economic
and/or military consequences of the lie. It thus becomes vitally
important for the State to use all of its powers to repress dissent, for
the truth is the mortal enemy of the lie, and thus by extension, the
truth is the greatest enemy of the State.

Joseph Goebbels




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On 01/08/2025 17:48, Mike Scott wrote:

On 01/08/2025 12:51, Theo wrote:

But realistically I'd probably use a 3.3 or 5V Songle relay. They are
uber cheap in bulk from Aliexpress.

Agreed, I think that's the simplest solution here.

I'm beginning to agree. I've been hunting round for prebuilt modules to
do the trick, and nothing provides isolation like a good old-fashioned relay. Maybe I just have to put up with the current drain.

Many thanks to all who've responded with ideas. I'll look around a bit
more, then press on with the relay bank.

Well its only 70mA a relay When its on
--
If you tell a lie big enough and keep repeating it, people will
eventually come to believe it. The lie can be maintained only for such
time as the State can shield the people from the political, economic
and/or military consequences of the lie. It thus becomes vitally
important for the State to use all of its powers to repress dissent, for
the truth is the mortal enemy of the lie, and thus by extension, the
truth is the greatest enemy of the State.

Joseph Goebbels




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From Newsgroup: comp.sys.raspberry-pi

On 01/08/2025 17:52, The Natural Philosopher wrote:
,,,

.

Well its only 70mA a relay When its on

x8 though, worst case. Over half an amp. Seemed a lot just to let some
current through to the tracks.



--
Mike Scott
Harlow, England
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From Newsgroup: comp.sys.raspberry-pi

Mike Scott <usenet.16@scottsonline.org.uk.invalid> wrote:

On 01/08/2025 14:49, David Higton wrote:

If you can drive relays momentarily but not continuously, consider
bistable relays.

I do have some, bought for another part of the project. But at IIRC ~£7
a pop, they're not cheap: I need 8.

I'm seeing things like this for searches of 'magnetic latching relay' for £1
a relay or £2 on a board with GPIO inputs:

https://www.aliexpress.com/item/1005009593982672.html https://www.aliexpress.com/item/1005005163980370.html

No experience, but I think there are some boards which do the latching digitally and then drive a conventional relay. These ones look like the
real deal.

You have to hold the latching inputs for a certain length of time - not sure what happens if you exceed the rated time, I don't know if there's a danger
of burning something out (railway modellers will perhaps be all too familiar with this idea from motorised points).

Theo
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Mike Scott <usenet.16@scottsonline.org.uk.invalid> wrote:

On 01/08/2025 17:52, The Natural Philosopher wrote:

Well its only 70mA a relay When its on

x8 though, worst case. Over half an amp. Seemed a lot just to let some current through to the tracks.

There are also "high sensitivity" type relays which can use less.

I repaired a modern model train controller a while ago and it had
a bank of mechanical relays inside. Variable speed control was done
with a very beefy set of MOSFETs in a H-bridge circuit, which had
nevertheless been blown apart when the owner hooked the power
supply up backwards.
--
__ __
#_ < |\| |< _#
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From Newsgroup: comp.sys.raspberry-pi

On 01/08/2025 19:25, Mike Scott wrote:

On 01/08/2025 17:52, The Natural Philosopher wrote:
,,,

.

Well its only 70mA a relay When its on

x8 though, worst case. Over half an amp. Seemed a lot just to let some current through to the tracks.

*shrug* subjective.

A Pi pico draws up to 2.5A

So you are faced with having a little 5V/2.5A PSU block on board anyway.

--
“Ideas are inherently conservative. They yield not to the attack of
other ideas but to the massive onslaught of circumstance"

- John K Galbraith


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On 02/08/2025 01:06, Computer Nerd Kev wrote:

beefy set of MOSFETs in a H-bridge circuit, which had
nevertheless been blown apart when the owner hooked the power
supply up backwards.

:-)
--
There is nothing a fleet of dispatchable nuclear power plants cannot do
that cannot be done worse and more expensively and with higher carbon emissions and more adverse environmental impact by adding intermittent renewable energy.

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From Newsgroup: comp.sys.raspberry-pi

In article <106hurs$9ibr$1@dont-email.me>,
Mike Scott <usenet.16@scottsonline.org.uk.invalid> wrote:

Hi - I'm working on a model railway project using pico boards, but have >spotted something that ought to be improved.

The power to each section of track is scheduled to be switched by a
relay. I've a bank of 8 traditional relays, but have just realized the
total relay current will be up to a half amp or so worst case. I'm
looking to a solid state solution.

The relays are switching DC at 12V, but the polarity is determined
before the on/off relay. Most SS relays I've seen are triac-based for AC >only; one type would do DC, but not with the polarity changing (and at
10x the cost anyway!).

Does anyone know anything solid state that might do this without
breaking the bank?

So you're looking for an AC SSR. Forget that the polarity is switched
before the relay as to all intents and purposes it's effectively AC.

The main issue I had when doing this on a Pi some years back was that all
the SSRs I used had a 5v input voltage with built-in limiting resistors on
the opto isolator part. Saying that, I didn't find one that wouldn't work
with the Pi's 3.3v output. I've no experience of the Picos outputs though.

I was switching 240v AC not 12v AC - and there is another issue - a lot of them are aimed at higher voltages - say 36-240v AC

Searching ebay find this for example:

https://www.ebay.co.uk/itm/166442394010

it's actually rated 3 to 32v input but the output is >= 24v AC so it may
not turn on at 12v. Also be aware that triac based ones may be relying
on the zero crossing to turn off, so once on, it might remain on even
when you remove the control voltage. I suspect the ones with GTO switches
are the more expensive ones.

Personally, I think that if I already had a working bank of mechanical
relays (with opto isolated inputs such as the multitude sold for Adruino
and Pi) I'd just suck it up and give it a separate 5v PSU capable
of driving the coils. (Or take the main system 5v and give it a good
decoupling from the electronics side to minimise any interferance).

Sure, it may well be a waste of energy but half an amp at 5 volts is a
mere 2.5 watts. Run that continually for a year and that's 22 KWh which
should be under a fivers worth of energy, but the chances of running it
like that are probably remote... (how much was the last coffee and cake
you bought?)

And mechanical relays will allow the passing of any DCC signals if you're
using that.

-Gordon
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On 02/08/2025 12:44, Gordon Henderson wrote:

In article <106hurs$9ibr$1@dont-email.me>,
Mike Scott <usenet.16@scottsonline.org.uk.invalid> wrote:

Hi - I'm working on a model railway project using pico boards, but have
spotted something that ought to be improved.

The power to each section of track is scheduled to be switched by a
relay. I've a bank of 8 traditional relays, but have just realized the
total relay current will be up to a half amp or so worst case. I'm
looking to a solid state solution.

The relays are switching DC at 12V, but the polarity is determined
before the on/off relay. Most SS relays I've seen are triac-based for AC
only; one type would do DC, but not with the polarity changing (and at
10x the cost anyway!).

Does anyone know anything solid state that might do this without
breaking the bank?

So you're looking for an AC SSR. Forget that the polarity is switched
before the relay as to all intents and purposes it's effectively AC.

The main issue I had when doing this on a Pi some years back was that all
the SSRs I used had a 5v input voltage with built-in limiting resistors on the opto isolator part. Saying that, I didn't find one that wouldn't work with the Pi's 3.3v output. I've no experience of the Picos outputs though.

I was switching 240v AC not 12v AC - and there is another issue - a lot of them
are aimed at higher voltages - say 36-240v AC

Searching ebay find this for example:

https://www.ebay.co.uk/itm/166442394010

it's actually rated 3 to 32v input but the output is >= 24v AC so it may
not turn on at 12v. Also be aware that triac based ones may be relying
on the zero crossing to turn off, so once on, it might remain on even
when you remove the control voltage. I suspect the ones with GTO switches
are the more expensive ones.

Personally, I think that if I already had a working bank of mechanical
relays (with opto isolated inputs such as the multitude sold for Adruino
and Pi) I'd just suck it up and give it a separate 5v PSU capable
of driving the coils. (Or take the main system 5v and give it a good decoupling from the electronics side to minimise any interferance).

Sure, it may well be a waste of energy but half an amp at 5 volts is a
mere 2.5 watts. Run that continually for a year and that's 22 KWh which should be under a fivers worth of energy, but the chances of running it
like that are probably remote... (how much was the last coffee and cake
you bought?)

And mechanical relays will allow the passing of any DCC signals if you're using that.

-Gordon

Remember that although a PI can only drive 3.3V it can happily (and
usually does) run off 5V.

I bought a load of these

https://www.aliexpress.com/item/1005006010491821.html

5V 3W.
I used a simple single NPN transistor and a couple of resistors to
drive the relays off 5V

I've found that drawing up a PCB for these sorts of things is so simple
that I dont even prototype them

You need a PSU and best practice is a suppression toroid, and
suppression cap and fuse on the mains side and a small smoothing cap on
the output side. and a diode to feed the PICO so that you can program it
with the power off.
Picos pins feed NPN transistor bases via resistive droppers and
collectors go to the relay coils and then to 5V.

The whole thing is a single neat circuit board . The pico solders onto
it using pins

If I don't need wifi I use the RP2040 Zero unless I need more pins to be accessible. Its cheap as chips
--
For every complex problem there is an answer that is clear, simple, and
wrong.

H.L.Mencken

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Gordon Henderson <gordon+usenet@drogon.net> wrote:

So you're looking for an AC SSR. Forget that the polarity is switched
before the relay as to all intents and purposes it's effectively AC.

I don't think you are. Regular AC SSRs use triac switching. The thing
about triacs is that once they're on they don't turn off until the current drops to (near) zero. For regular AC that's the zero crossing point and happens every 20ms on 50Hz mains. But for variable-polarity DC it's a
constant current and so the triac doesn't turn off while the current is
there. It will next time the current goes to zero, but that may never
happen.

GTO (gate turnoff) thyristors are an old way to handle that, but they're
really for electric locomotive scale applications, not small scale
stuff. That's what got me thinking about IGBTs.

The main issue I had when doing this on a Pi some years back was that all
the SSRs I used had a 5v input voltage with built-in limiting resistors on the opto isolator part. Saying that, I didn't find one that wouldn't work with the Pi's 3.3v output. I've no experience of the Picos outputs though.

Some of them have 3-24V inputs. I think the Crydom ones I have do that.

I was switching 240v AC not 12v AC - and there is another issue - a lot of them
are aimed at higher voltages - say 36-240v AC

Searching ebay find this for example:

https://www.ebay.co.uk/itm/166442394010

Those are fakes and lie about their ratings, FYI. OK if you don't take them anywhere near rated current. Also the baseplate needs heatsinking as it's
just a single triac with the markings filed off.

it's actually rated 3 to 32v input but the output is >= 24v AC so it may
not turn on at 12v. Also be aware that triac based ones may be relying
on the zero crossing to turn off, so once on, it might remain on even
when you remove the control voltage. I suspect the ones with GTO switches
are the more expensive ones.

Do small GTO SSRs even exist as a product? The only GTOs I can find are tens/hundreds/thousands of pounds?

Personally, I think that if I already had a working bank of mechanical
relays (with opto isolated inputs such as the multitude sold for Adruino
and Pi) I'd just suck it up and give it a separate 5v PSU capable
of driving the coils. (Or take the main system 5v and give it a good decoupling from the electronics side to minimise any interferance).

+1. Or bistable relays if the coil current is a nonstarter.

And mechanical relays will allow the passing of any DCC signals if you're using that.

There is that.

Theo
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On 02/08/2025 12:44, Gordon Henderson wrote:

Personally, I think that if I already had a working bank of mechanical
relays (with opto isolated inputs such as the multitude sold for Adruino
and Pi) I'd just suck it up and give it a separate 5v PSU capable

Yes, sound advice. Thanks. I was working out late last night this will
be outside a normal usb current limit. I do have a suitable bank of
relays, and I'm pretty sure there must be a spare 5V wall wart around somewhere.

Thanks to all for comments offered. I think I'll have to stick to the old-fashioned way here.
--
Mike Scott
Harlow, England
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On 01/08/2025 21:47, Theo wrote:

Mike Scott <usenet.16@scottsonline.org.uk.invalid> wrote:

On 01/08/2025 14:49, David Higton wrote:

If you can drive relays momentarily but not continuously, consider
bistable relays.

I do have some, bought for another part of the project. But at IIRC ~£7
a pop, they're not cheap: I need 8.

I'm seeing things like this for searches of 'magnetic latching relay' for £1 a relay or £2 on a board with GPIO inputs:

https://www.aliexpress.com/item/1005009593982672.html

"Sorry, this item's currently unavailable in your location.".

https://www.aliexpress.com/item/1005005163980370.html

That looks a good possibility, thanks. I do see that ali offer these on
a module as well, with added components. I'll have to check the
datasheet, but I imagine the pico won't drive the relay coils directly.
It's also £4 a pop on a module. x8.

No experience, but I think there are some boards which do the latching digitally and then drive a conventional relay. These ones look like the
real deal.

You have to hold the latching inputs for a certain length of time - not sure what happens if you exceed the rated time, I don't know if there's a danger of burning something out (railway modellers will perhaps be all too familiar with this idea from motorised points).

So I imagine. I bought a board that charges a big capacitor, then uses
that to run the point motor, automatically cutting off the charging
power when current is drawn. Then you can't burn them out. The currents
are really quite large: a SEEP motor seems to be about 2 ohms for the
coil, and I'm running from a 19V psu, so we're talking around 10amps.
For that, I'm using some overly beefy mosfet modules. A much simpler
problem than steering power to the tracks. I have a pico-based control
board to control 6 points with USB to a desktop pc. Works well in testing.


I'll give the relay modules a bit more thought. Thanks.
--
Mike Scott
Harlow, England
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On 04/08/2025 09:04, Mike Scott wrote:

On 02/08/2025 12:44, Gordon Henderson wrote:

Personally, I think that if I already had a working bank of mechanical
relays (with opto isolated inputs such as the multitude sold for Adruino
and Pi) I'd just suck it up and give it a separate 5v PSU capable

Yes, sound advice. Thanks. I was working out late last night this will
be outside a normal usb current limit. I do have a suitable bank of
relays, and I'm pretty sure there must be a spare 5V wall wart around somewhere.

Thanks to all for comments offered. I think I'll have to stick to the old-fashioned way here.

I've got bare pcbs with a 5V psu and buffered 4 buffered relay coils
that can interface to a Pi if you want

Supply the voltage and have transistors and LEDS to drive and show relay status

http://vps.templar.co.uk/Odd%20stuff/HC.JPG

Its interfacing to a zero there, but a Pico can run off 5V as well
--
“it should be clear by now to everyone that activist environmentalism
(or environmental activism) is becoming a general ideology about humans,
about their freedom, about the relationship between the individual and
the state, and about the manipulation of people under the guise of a
'noble' idea. It is not an honest pursuit of 'sustainable development,'
a matter of elementary environmental protection, or a search for
rational mechanisms designed to achieve a healthy environment. Yet
things do occur that make you shake your head and remind yourself that
you live neither in Joseph Stalin’s Communist era, nor in the Orwellian utopia of 1984.”

Vaclav Klaus

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From Newsgroup: comp.sys.raspberry-pi

On 04/08/2025 11:10, The Natural Philosopher wrote:

On 04/08/2025 09:04, Mike Scott wrote:

On 02/08/2025 12:44, Gordon Henderson wrote:

Personally, I think that if I already had a working bank of mechanical
relays (with opto isolated inputs such as the multitude sold for Adruino >>> and Pi) I'd just suck it up and give it a separate 5v PSU capable

Yes, sound advice. Thanks. I was working out late last night this will
be outside a normal usb current limit. I do have a suitable bank of
relays, and I'm pretty sure there must be a spare 5V wall wart around
somewhere.

Thanks to all for comments offered. I think I'll have to stick to the
old-fashioned way here.

I've got bare pcbs with a 5V psu and buffered 4 buffered relay coils
that can interface to  a Pi if you want

Supply the voltage and have transistors and LEDS to drive and show relay status

http://vps.templar.co.uk/Odd%20stuff/HC.JPG

Its interfacing to a zero there, but a Pico can run off 5V as well

Thanks for the offer, but as I already have the 8-way bank, I'll settle
for that.
--
Mike Scott
Harlow, England
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: comp.sys.raspberry-pi

On 04/08/2025 13:50, Mike Scott wrote:

On 04/08/2025 11:10, The Natural Philosopher wrote:

On 04/08/2025 09:04, Mike Scott wrote:

On 02/08/2025 12:44, Gordon Henderson wrote:

Personally, I think that if I already had a working bank of mechanical >>>> relays (with opto isolated inputs such as the multitude sold for
Adruino
and Pi) I'd just suck it up and give it a separate 5v PSU capable

Yes, sound advice. Thanks. I was working out late last night this
will be outside a normal usb current limit. I do have a suitable bank
of relays, and I'm pretty sure there must be a spare 5V wall wart
around somewhere.

Thanks to all for comments offered. I think I'll have to stick to the
old-fashioned way here.

I've got bare pcbs with a 5V psu and buffered 4 buffered relay coils
that can interface to  a Pi if you want

Supply the voltage and have transistors and LEDS to drive and show
relay status

http://vps.templar.co.uk/Odd%20stuff/HC.JPG

Its interfacing to a zero there, but a Pico can run off 5V as well

Thanks for the offer, but as I already have the 8-way bank, I'll settle
for that.

Great.
--
Of what good are dead warriors? … Warriors are those who desire battle
more than peace. Those who seek battle despite peace. Those who thump
their spears on the ground and talk of honor. Those who leap high the
battle dance and dream of glory … The good of dead warriors, Mother, is
that they are dead.
Sheri S Tepper: The Awakeners.

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