# 8 channel relay board.



## Cole&Jacksdad (Jan 20, 2011)

Is this a good deal on a SSRB?
Amazon.com: SainSmart 8-Channel 5V Solid State Relay Module Board for Arduino ARM DSP PIC: [email protected]@[email protected]@http://ecx.images-amazon.com/images/I/[email protected]@[email protected]@51oeultoy8L


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## robp790 (Jan 8, 2008)

*good price*

I think it is. I ordered one to try with my Picaxe controller. Bad news is that it will take 8 pins to send the control signals to the relay board. But, if that is all my controller is doing it should not be a problem.


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## Atom058 (Sep 20, 2009)

And, if I am not mistaken, it will only control AC devices...


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## hedg12 (Jul 6, 2008)

Atom058 said:


> And, if I am not mistaken, it will only control AC devices...


Yup, AC only up to 2 amps. Most solid state relays (with a few exceptions) are AC only on the load side. Still a good deal.


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## alwomack (Feb 12, 2012)

robp790 said:


> I think it is. I ordered one to try with my Picaxe controller. Bad news is that it will take 8 pins to send the control signals to the relay board. But, if that is all my controller is doing it should not be a problem.


You should be able to use the 74HC595 shift register. You will need only 3 pins on the Picaxe.


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## robp790 (Jan 8, 2008)

Well, that looks cool. I was doing research on serial control of multiple picaxe boards. I will have to search for some applications using picaxe and the 74HC595 shift register. Have anyone here used this???


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## robp790 (Jan 8, 2008)

So I did more research, and if this works, apparently I can chain 1000 chips and have control over 8000 pins. Pins = outputs. I have ordered 3 chips from my local electronics store to arrive in 5 days. I will hook it up and see if I can get 3 pins from my picaxe to control all 12 relays. I have the board from the Amazon site and one from Mdfly.com that cost $12 for four relays, not solid state though.


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## pshort (May 6, 2008)

robp790 said:


> So I did more research, and if this works, apparently I can chain 1000 chips and have control over 8000 pins. Pins = outputs. I have ordered 3 chips from my local electronics store to arrive in 5 days. I will hook it up and see if I can get 3 pins from my picaxe to control all 12 relays. I have the board from the Amazon site and one from Mdfly.com that cost $12 for four relays, not solid state though.


You're not going to get anywhere 8000 channels without a lot of care and attention to low-level hardware details. There will be significant signal integrity issues with 1000 chips sitting on each of the bit clock and output latch signals of the 595 chip. 1000 chips implies a lot of capacitance due to both the wire length and to the number of IC inputs connected to the wire. I wouldn't go much beyond about 10 chips (if they're close together) without some sort of buffer or other signal regeneration scheme.


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## TheOneAndOnlyKelly (May 7, 2009)

Check out some of the rigs they have over at http://doityourselfchristmas.com/. They have set ups with 100s of channels.

One thing to note if you are going to be daisy chaining a lot of the control boards is you are going to get a lot of lag between initial instruction and hardware response, especially the further down the chain you are. That's a big issue especially if you are trying to sync lights or motion to sound or music.


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## robp790 (Jan 8, 2008)

There is always limitations to technology. I was only impressed with the _possibilities_ of a series of chips. I could not in the near future, use so many outputs. The possibilities of using 3 pins from a $12 picaxe to control my 12 relays with possibilities for more just makes me smile. This is why I enjoy this forum to learn from all of you.


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## pshort (May 6, 2008)

There is another thing to consider (although I don't think that it will cause you problems) - many of the 595 chips are spec'd for a maximum of 70 mA through the power and ground pins. Based on its input resistance, the input current for each SSR on that Sain board will take around 10 mA. If all 8 outputs are on at once, the current through the power pin of the 595 would be 80 mA or so, a little bit high for that part. That is beyond the spec for many 595 chips, although I don't think that you would encounter any problems in practice. The SSRs used over at doityourselfchristmas.com are usually designed for 6mA of input current for this very reason (and because other parts commonly used there have similar limitations).

In any case, I think that the 595 chips are a good part to use for this application.


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