mblyman89
Posts: 3
Joined: Mon Apr 01, 2019 5:16 pm

rasberry pi controlling 50 relays

Mon Apr 01, 2019 5:30 pm

Hello, I am very new to circuits and rpi, I have never used any of these components before. I am curious if one rasberry pi can control 50 relays. I want to network 10 resberry pi's together in a dramble, where each rpi controls a bank of 50 relays. I have done a little digging, and it looks like I can use a shift register to bridge between the rpi and a bread/perf board, that can then run multiple 16 channel relays? And then I would also use the breadboard as a power supply to supply power to the second half of each of the 16 channel relays? Long story short, I am using this as a means to launch fireworks for the 4th, so I don't need heavy computing power, nor do I need to supply a large load for each bank, just enough current to heat a small piece of nichrom wire. Is something like this possible?

Thank you!

LTolledo
Posts: 1548
Joined: Sat Mar 17, 2018 7:29 am

Re: rasberry pi controlling 50 relays

Mon Apr 01, 2019 10:03 pm

better explore using I2C I/O expander IC MCP23017, as 1 of these can expand your I/O by 16.

a single RPi with 8 x MCP23017 can have as much as 128 outputs (excluding the unused GPIO pins of the RPi)

if you add SPI version (MCP23S17) you can have more outputs on a single RPi

you can search the forum (I think it was discussed here too) for more details.
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boyoh
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Re: rasberry pi controlling 50 relays

Tue Apr 02, 2019 2:46 pm

There is the possibility of using Sequential logic for this project
Other than using power hungry relays, You could use Decade
Counters switching transistors to fire the Fireworks The counters
could be controlled by timed clock pulses The counter can be cascaded
or parcelled as many as you want. A pulse generator switching
logic gates will be very useful for this project

Regards BoyOh
BoyOh ( Selby, North Yorkshire.UK)
Some Times Right Some Times Wrong

boyoh
Posts: 1284
Joined: Fri Nov 23, 2012 3:30 pm
Location: Selby. North Yorkshire .UK

Re: rasberry pi controlling 50 relays

Tue Apr 02, 2019 2:47 pm

There is the possibility of using Sequential logic for this project
Other than using power hungry relays, You could use Decade
Counters switching transistors to fire the Fireworks The counters
could be controlled by timed clock pulses The counter can be cascaded
or parcelled as many as you want. A pulse generator switching
logic gates will be very useful for this project

Regards BoyOh
BoyOh ( Selby, North Yorkshire.UK)
Some Times Right Some Times Wrong

User avatar
NGC6543
Posts: 75
Joined: Thu Feb 28, 2019 7:30 pm
Location: Lancashire, UK

Re: rasberry pi controlling 50 relays

Tue Apr 02, 2019 3:41 pm

Yes, there are a few ways to tackle this. A bank of 74HC595 can be daisy chained. A possibly useful aspect of those is the Output Enable, to keep the outputs high impedance while the data is clocked in and then all fired together by setting the OE pin.

I would throw a MAX EPM7128AE CPLD (or similar) at the issue though, configured to do the whole logic job in a single 68-pin socketable PLCC chip. Cheap enough and easier to lay out a board for.

To fire the igniters I would probably go for a bank of stiff MOSFETs or darlingtons. I would also try to add into the system a manual disable/enable switch, easy to do with the CPLD or the 74HC595 solution, and a kill switch on the main power.

What's the resistance of the nichrome igniter? Usually 0.5Ω to a couple I think.

mblyman89
Posts: 3
Joined: Mon Apr 01, 2019 5:16 pm

Re: rasberry pi controlling 50 relays

Wed Apr 03, 2019 9:26 pm

Thank you for the responses! I have a picture of what i am trying to build, I am having a hard time understanding two things in the picture and am hoping one of you will be able to tell me what they are, and what they are for. Also, what is the yellow wire that goes from each relay for? Thank you for the help!
Attachments
project example pic.jpg
Thank you!
project example pic.jpg (67.28 KiB) Viewed 232 times

LTolledo
Posts: 1548
Joined: Sat Mar 17, 2018 7:29 am

Re: rasberry pi controlling 50 relays

Wed Apr 03, 2019 10:03 pm

Glass fuse on the right, simple over current protection

the white connector with yellow and white wires looks like AC common (connected to all relays)
the black connector could be the other side of the AC line.

One wrong move and you'll have a "shocking experience "

control circuits of that type are best installed inside an IP44 (or even IP55 for outdoor use) electrical enclosures
"Don't come to me with 'issues' for I don't know how to deal with those
Come to me with 'problems' and I'll help you find solutions"

Some people be like:
"Help me! Am drowning! But dont you dare touch me nor come near me!"

mblyman89
Posts: 3
Joined: Mon Apr 01, 2019 5:16 pm

Re: rasberry pi controlling 50 relays

Thu Apr 04, 2019 12:41 am

Thank you for the advise! I will make sure to include a safety enclosure as well as a key switch and a three way switch for arming and testing the device. Thank you again for the help.

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rpdom
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Location: Chelmsford, Essex, UK

Re: rasberry pi controlling 50 relays

Thu Apr 04, 2019 6:52 am

LTolledo wrote:
Wed Apr 03, 2019 10:03 pm
control circuits of that type are best installed inside an IP44 (or even IP55 for outdoor use) electrical enclosures
Also they would use circuit boards, not breadboards with fragile connections.

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