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by Wizards Hat
Sun Feb 10, 2019 8:02 pm
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Re: Relay Line out voltage causing voltage on line in

I've ordered some of the 55-32's - slightly cheaper from rapid (using my education account) as I needed a few other bits & pieces from there anyway - they have a lead time of 5-7 days - which is ok for me as I'm back to work tomorrow & probably need to dedicate a few weeks attention away from my pr...
by Wizards Hat
Mon Jan 07, 2019 5:08 pm
Forum: Astro Pi
Topic: Measure Urbanisation with NoIR camera
Replies: 3
Views: 1371

Re: Measure Urbanisation with NoIR camera

What's stopping you diffracting the light?

Surely you could use a diffraction grating (& camera/CCD) to get a spectrograph?

Regards,
Dan.
by Wizards Hat
Mon Jan 07, 2019 6:42 am
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Re: Relay Line out voltage causing voltage on line in

Brandon92 wrote:
Mon Jan 07, 2019 6:18 am
Did you also buy the required relay socket to connect the wires to this relay?

https://uk.farnell.com/finder/94-84-3sp ... dp/9137661
Yes, I got the sockets too.
Thanks,
Dan.
by Wizards Hat
Mon Jan 07, 2019 6:42 am
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Re: Relay Line out voltage causing voltage on line in

Also don't forget the reversed biased diode across the coil of the relay. This wasn't shown in the schematic. Standard practice is to locate the diode as close to the relay coil as possible. The ULN chip has these built in, but they are located on the chip, and I wouldn't depend on them...... ok - ...
by Wizards Hat
Sun Jan 06, 2019 10:06 pm
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Re: Relay Line out voltage causing voltage on line in

This relay will switch 7A of resistive load at 240V AC which is about 1600W and seeing as it has 4 contacts you could common them together to switch even more. https://uk.farnell.com/finder/55-34-9-012-0040/relay-4pdt-250vac-7a/dp/1169225?MER=bn_para_1TP_LastViewed_1 Personally, I would not add the...
by Wizards Hat
Sun Jan 06, 2019 4:58 pm
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Re: Relay Line out voltage causing voltage on line in

...would appreciate suggestions from anyone as to what specific relays to actually use - there seems to be a huge choice & I'm not sure why to choose one over another. => want to be able to control a 400W smoke machine (so assume ~2A), light bulb & extractor fan (~20W)...all on separate switches. D...
by Wizards Hat
Sun Jan 06, 2019 3:54 pm
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Re: Relay Line out voltage causing voltage on line in

That's brilliant - thanks Bob. I've bought some ULN2803A chips - just need to decide on what relays to get now. Why do you suggest the "octal" ones?...seems like a much reduced/limited choice ...would appreciate suggestions from anyone as to what specific relays to actually use - there seems to be a...
by Wizards Hat
Tue Jan 01, 2019 8:20 pm
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Re: Relay Line out voltage causing voltage on line in

If you really need to switch mains voltages then I suggest you look at octal relays, they mount on individual bases with screw terminals. I would look to use ones with 12v DC coils, then use a separate 12v PSU to power them and a uln2803A to interface the pi gpio to the 12v switching the ground sid...
by Wizards Hat
Tue Jan 01, 2019 6:45 pm
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Re: Relay Line out voltage causing voltage on line in

My first reaction would be to sling that board in the bin, as far away from mains as possible! Fair enough about binning the board - what would you suggest in its place? For my project I need to be able to turn on/off mains operated smoke machine, fan & lights. But ... can you measure any resistanc...
by Wizards Hat
Tue Jan 01, 2019 6:42 pm
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Re: Relay Line out voltage causing voltage on line in

Thanks for the suggestions... Maybe a very stupid question, but are the battery in your multimeter not empty. Because this could result in very strange measurement. Erm...ok...not thought of that, but just changed it & get the same readings. And what is the voltage across DS7. Because when you measu...
by Wizards Hat
Tue Jan 01, 2019 5:19 pm
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Re: Relay Line out voltage causing voltage on line in

Hopefully you can see the attached picture - when there is NOTHING else connected to the relay other than the 240V line out (UK mains)..on ANY of the channels, there is a voltage between GND-In(all) of line in ...when taking this picture it was 1.25V. https://i.imgur.com/lKOrDj9.jpg Can't seem to fi...
by Wizards Hat
Tue Jan 01, 2019 3:59 pm
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Re: Relay Line out voltage causing voltage on line in

Appreciate the response Bob... ....I do realise the danger involved even though I have no "official" training on electrical wiring...but I am a very experienced physics teacher (& therefore a degree in physics too) & very much understand what not to do. I have been trying to research this problem fo...
by Wizards Hat
Tue Jan 01, 2019 1:35 pm
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 1836

Relay Line out voltage causing voltage on line in

I think I have a problem with voltage noise passing between supposedly isolated parts of a relay & don't know how to get rid of it. I have recently bought a standard 5V relay module board (8-channel)* and can control it without issue using an mcp23017 connected to the pi (3). However, when I connect...

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