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Author Topic: 8 Channel Relay Board - Proofreading  (Read 11247 times)
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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?
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Hmmm.  Ok CrossRoads you lost me at Tx..  I feel retarded but what Tx are you talking about?
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Hmmm.  Ok CrossRoads you lost me at Tx..  I feel retarded but what Tx are you talking about?

Your node names, T1-T8.
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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

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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 (268.81 KB - downloaded 46 times.)
« Last Edit: April 14, 2013, 08:20:19 pm by codlink » Logged

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According to the datasheets:

4N37S has 100mA collector current
The relay needs 150mA
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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.
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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.
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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
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Ah, much better. No short circuit either.  smiley
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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.

Edited: Sorry, that was poorly worded. I meant notice how the collector on the ebay circuit is wired to 5 V and their emitter goes to the base of the driver transistor as opposed to the way your circuit is wired.

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So, for example R16 (T16) needs to be pulled high?

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.

Edited: Sorry, that was poorly worded. I meant notice how the collector on the ebay circuit is wired to 5 V and their emitter goes to the base of the driver transistor as opposed to the way your circuit is wired.

Ah, I understand now.  I attached a schematic of which I was basing mine off of.

Now my first sentence on this post would rectify the situation, pulling (T16 for example) high?  Since you can't see (lol), the wire going from the collector to the base of the relay transistor.


* avr-io-b-sch.gif (38.61 KB, 1624x1127 - viewed 64 times.)
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I see how you got confused. Notice they are biasing the phototransistor to switch faster rather than act more linearly. I don't know what the purpose of the Olimex circuit is. It's an optically coupled OR-gate that resets the processor for whatever reason I don't know. smiley
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I see how you got confused. Notice they are biasing the phototransistor to switch faster rather than act more linearly. I don't know what the purpose of the Olimex circuit is. It's an optically coupled OR-gate that resets the processor for whatever reason I don't know. smiley

Not quite. It's poorly drawn. Note that each opto collector has a I1, I2, I3, or I4 label. These wire over to digital input pins on the processor chip.
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How do you say it's poorly drawn?
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