8 Channel Relay Board - Proofreading

Projects & Topics Product Design
#1

I have drawn up an 8 channel relay board from a couple of different schematics and wanted another set of eyes to proofread it for me. It is an opto-isolated system that will be controlling 24V max.

I have never used a relay with an Arduino and I would rather design my own ckt than to just buy one. As I am aware, this should be an active-low layout. Are my assumptions correct?
The IN1-IN8 are the Arduino inputs and +5V will come from a Power supply. VCC will come from Arduino’s supply.

Any advice or constructive criticism is welcome.

Relay Board.sch (988 KB)

relay.png
relay.png1161×898 41.7 KB

#2

Design looks ok. Use a picture hosting side without so much spam. Or just attach the pictures to your post: Click "Additional Options", browse to your attachment.

#3

I guess I'm blind today.

#4

CrossRoads: Design looks ok. Use a picture hosting side without so much spam. Or just attach the pictures to your post: Click "Additional Options", browse to your attachment.

I apologize CrossRoads. I have been using postimg for years now and never had any spam on my screen. Of course, I use FireFox with around 5 anti-spam/pop-up/ads extensions. I am one person that hates ads and pop-ups. I turned off the blockers and reloaded the page and didn't see anything. But, I am sorry.

I don't like use the attachment feature when I need to upload large pics as I hate to scroll all over it to see it.

Also, thanks for the extra set of eyes. +1

[quote author=Papa G link=topic=160464.msg1201122#msg1201122 date=1365966117] I guess I'm blind today. [/quote]

Looking at what?

#5

How is scrolling all over an external website any different than scrolling all over in here? In both cases it's too big. Export the picture in eagle so that it comes out ~ 800 pixels wide. You can modify your post to remove the external pic, and attach the smaller schematic. I've gone back & "Modify"'d lots of my posts that came out a lot bigger than I thought.

#6

codlink: [quote author=Papa G link=topic=160464.msg1201122#msg1201122 date=1365966117] I guess I'm blind today.

Looking at what? [/quote]

It looks like the schematic is incomplete around the opto-isolator.

#7

I don't think so - just uses names on the nets vs drawing lines all over the place. Easy to follow. The IN and VCC/5V headers could have been drawn on the left side of the page to show signal flow a little better, is the only change I would have made.

#8

I hadn't thought about everyone having the same size screen as I.

Original post modified with updated schematic.

#9

That turned out well.

#10

Curious, what is pin 6 on the opto used for? Should I leave it floating?

#11

Leave it floating.

#12

codlink: Curious, what is pin 6 on the opto used for? Should I leave it floating?

You can use it to bias the BE junction by placing a resistor from the base to the emitter and reduce the sensitivity to low level LED light and hence produce a sharper switching action. Normally it is left unconnected.

#13

CrossRoads: I don't think so - just uses names on the nets vs drawing lines all over the place. Easy to follow. The IN and VCC/5V headers could have been drawn on the left side of the page to show signal flow a little better, is the only change I would have made.

It's not clear to me how any current ever flows in the collector of the phototransistor. It looks like there is a missing resistor.

#14

[quote author=Papa G link=topic=160464.msg1201490#msg1201490 date=1365986529]

CrossRoads: I don't think so - just uses names on the nets vs drawing lines all over the place. Easy to follow. The IN and VCC/5V headers could have been drawn on the left side of the page to show signal flow a little better, is the only change I would have made.

It's not clear to me how any current ever flows in the collector of the phototransistor. It looks like there is a missing resistor.

[/quote]

Yep, no current source to be seen for the opto collector to relay npn base connection. That dog won't bark.

Lefty

#15

retrolefty: [quote author=Papa G link=topic=160464.msg1201490#msg1201490 date=1365986529]

CrossRoads: I don't think so - just uses names on the nets vs drawing lines all over the place. Easy to follow. The IN and VCC/5V headers could have been drawn on the left side of the page to show signal flow a little better, is the only change I would have made.

It's not clear to me how any current ever flows in the collector of the phototransistor. It looks like there is a missing resistor.

Yep, no current source to be seen for the opto collector to relay npn base connection. That dog won't bark.

Lefty [/quote]

I was hoping OP would catch it. I gave a couple of hints. It's better when you figure it out for yourself, I think.

#16

Yes, resistors from Tx to +5 are needed. That would turn on relays all the time (to the NO position) until the INx signals go Low to turn on the Opto and turn off the NPNs. Can the Opto's drive the relay coils directly & skip the level of inversion?

#17

Hmmm. Ok CrossRoads you lost me at Tx… I feel retarded but what Tx are you talking about?

#18

codlink: Hmmm. Ok CrossRoads you lost me at Tx.. I feel retarded but what Tx are you talking about?

Your node names, T1-T8.

#19

CrossRoads: Yes, resistors from Tx to +5 are needed. That would turn on relays all the time (to the NO position) until the INx signals go Low to turn on the Opto and turn off the NPNs. Can the Opto's drive the relay coils directly & skip the level of inversion?

Probably not but datasheet would tell if collector is rated at or above coil current required.

The circuit really should be designed to default to all relays off when there is no opto input signal. Look towards the end of this e-bay listing for a typical schematic wiring design that should be used. http://www.ebay.com/itm/4-Channel-5V-Relay-Module-With-Optocoupler-For-Arduino-DSP-AVR-PIC-ARM-/221200546982?pt=LH_DefaultDomain_0&hash=item3380947ca6

Lefty

#20

Sorry, but I don’t see any difference in the Ebay ckt to mine. The only thing that I see is that I have a LED and a resistor for the LED on the relay.

Also I don’t see (nor have I ever seen) pull-up resisitors on the Inputs.

Not trying negative but I would like to understand.

I attached the opto I am using.

4N37S (Opto).pdf (269 KB)