8 Channel Relay Board - Proofreading

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.

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.

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

Original post modified with updated schematic.

That turned out well.

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

Leave it floating.

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.

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 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

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.

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?

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

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

Your node names, T1-T8.

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

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)

According to the datasheets:

4N37S has 100mA collector current The relay needs 150mA

codlink: 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.

The circuit is pretty hard to see for me and I think there is a mistake in it anyway. It looks like the wire shorting out the relay coil shouldn't be there. Notice where the collector of the phototransistor goes and notice that the emitter is not grounded.

The e-bay circuit has the opto collecto connected to +5, and the emitter driving the base of the NPN transistor. Opto LED on = current flowing into the NPN Base. Your design had Otpo LED on turning the NPN base off (low) with nothing to bring it high.

This listing has a clearer picture:

http://www.ebay.com/itm/8-Channel-DC-5V-Relay-Module-for-Arduino-PIC-ARM-DSP-AVR-MSP430-TTL-Logic-/271188081780?pt=LH_DefaultDomain_0&hash=item3f2411bc74

Lefty

retrolefty: This listing has a clearer picture:

http://www.ebay.com/itm/8-Channel-DC-5V-Relay-Module-for-Arduino-PIC-ARM-DSP-AVR-MSP430-TTL-Logic-/271188081780?pt=LH_DefaultDomain_0&hash=item3f2411bc74

Lefty

Ah, much better. No short circuit either. :)