I need a relay.

[killivolt]

I was thinking I could pick one out myself but I should have known it would be more complicated.

I have a 5vdc 400ma supply from a status Pin on a parrellel port. I have a voltage I intend to pull to ground using Isolated relay contacts.

The relay's I have been looking at are bigger than the supply voltage I want to use.


Any suggestions.

kv

 

[duffy]

Digikey has HUNDREDS of different 5V relays in stock, with pictures and spec sheets. Type "relay" into their search bar, then click on "Power" or "Signal" (one's greater than 2A, one's less) and start narrowing it down. You will need to know the current you are switching, and the voltage.

 

[Willbe]

You will need to know the current you are switching, and the voltage.

And the load: resistive, inductive, tungsten, motor.

 

[Boncuk]

Hi killivolt,

that's a good opportunity to change the login-name at the forum. Connect a relay directly to any pin of the parallel interface and you will deserve the name "how-to-kill-an-UART".

In other words, you will most likely have to look for a new mainboard for your PC if you do that.

The UART can only drive small currents and the coil resistance of a reed-relay is not high enough to keep the current within safe limits.

This is the safe way to use the parallel interface: Use a buffer circuit (74HC125 or 74HC244) as shown in the attached sample circuit.

Boncuk

 

[killivolt]

Hi killivolt,

that's a good opportunity to change the login-name at the forum. Connect a relay directly to any pin of the parallel interface and you will deserve the name "how-to-kill-an-UART".

In other words, you will most likely have to look for a new mainboard for your PC if you do that.

The UART can only drive small currents and the coil resistance of a reed-relay is not high enough to keep the current within safe limits.

This is the safe way to use the parallel interface: Use a buffer circuit (74HC125 or 74HC244) as shown in the attached sample circuit.

Boncuk

I have a 12 volt dc supply but they are not on the same ground plane. How can I do this with a different 12 volt supply. How do I isolate it ?

kv

Edit: I meant to Thank you for your Help.

Thanks, Boncuk for the schematic.

 

[duffy]

Actually, there are dozens of relays that can run directly off a port pin. Look for one that uses less than 20ma of current. It will probably be a "reed relay". Don't forget to include a freewheeling diode (points up from ground across the coil) so you aren't relying on the body-drain diodes on the port pin to do the job.

 

[killivolt]

Actually, there are dozens of relays that can run directly off a port pin. Look for one that uses less than 20ma of current. It will probably be a "reed relay". Don't forget to include a freewheeling diode (points up from ground across the coil) so you aren't relying on the body-drain diodes on the port pin to do the job.

Thanks for the help duffy. My trouble is this isn't actually off a pc it's from a audio mixer we use at the University. My problem is I only have the 5v supply 400ma that is supplied by the manufacturer which is designed to run with relay's as per the operational instructions.

However, I do like the Idea of building a more usable safe circuit as suggested. But only if it were a pc I could pull the 12v off one of supply line rails.


kv

 

[Leftyretro]

Hi killivolt,

that's a good opportunity to change the login-name at the forum. Connect a relay directly to any pin of the parallel interface and you will deserve the name "how-to-kill-an-UART".

In other words, you will most likely have to look for a new mainboard for your PC if you do that.

The UART can only drive small currents and the coil resistance of a reed-relay is not high enough to keep the current within safe limits.

This is the safe way to use the parallel interface: Use a buffer circuit (74HC125 or 74HC244) as shown in the attached sample circuit.

Boncuk

Your advice is right on, however your use of the word UART is wrong as a UART (universal asynchronous receiver transmitter) is a hardware component associated with a serial port, not a parallel port. Parallel ports use rather standard TTL drivers and receivers, not a UART device.

Lefty

 

[killivolt]

Your advice is right on, however your use of the word UART is wrong as a UART (universal asynchronous receiver transmitter) is a hardware component associated with a serial port, not a parallel port. Parallel ports use rather standard TTL drivers and receivers, not a UART device.

Lefty

Lefty I just did a search on separating sources and ground planes and I came up with a circuit that used shot key diodes. Do you think I could implement them into my circuit ?

Edit: I think this won't work. However, I have been looking at maybe Dc to Dc transformers to isolate my sources or Is my ship sunk ?

 

[Leftyretro]

Lefty I just did a search on separating sources and ground planes and I came up with a circuit that used shot key diodes. Do you think I could implement them into my circuit ?

Edit: I think this won't work. However, I have been looking at maybe Dc to Dc transformers to isolate my sources or Is my ship sunk ?

KV;

I'm having a hard time figuring out exactly what (and how) you are trying to do. A drawing would really help.

Lefty

 

[killivolt]

KV;

I'm having a hard time figuring out exactly what (and how) you are trying to do. A drawing would really help.

Lefty

Right, limited time and family. Home computer is in the Kitchen.

I got a grandchild in my lap. I have been working none stop for so long I can't remember.

I put in about 48 hours no sleep. I'm just starting to catch up. Now I need this circuit to work.

My problems and not yours. But if it was so easy it would be done right now.

I may have to look for another solution.

Thanks for the reply. kv

Edit: When I said right, that is to say I do need to do that. My apology's.

 

[Boncuk]

Hi killivolt,

using different ground planes you might replace the transistor in my schematic with the diode of a low current optocoupler. Connect its transistor to the 12 power supply and its ground.

Normally optocouplers can't drive a relay directly, so use another transistor at the optocoupler output to drive the relay.

If the signal is inverted and the relay driven opposite its actuation cycle use an inverter right behind the buffer.

Boncuk

 

[killivolt]

Hi killivolt,

using different ground planes you might replace the transistor in my schematic with the diode of a low current optocoupler. Connect its transistor to the 12 power supply and its ground.

Normally optocouplers can't drive a relay directly, so use another transistor at the optocoupler output to drive the relay.

If the signal is inverted and the relay driven opposite its actuation cycle use an inverter right behind the buffer.

Boncuk

I was actually looking at the opto-couplers but I didn't understand how I could make it work. I'll try to draw out a circuit with what I'm trying to accomplish as soon as I'm able.

Thanks for the help. Bancuk,........... n (Lefty)

Cheers,

kv

 

[killivolt]

Maybe with a little luck.

Ok, found out that I have two 5 vdc 400ma pins on the unit.

If I take a parallel off vcc to the relay in the diagram and use a cc1124-nd Digikey reed relay ?

Both sharing the same ground plane. Will this relay be good or is there a better choice ?


kv

 

[duffy]

Looks good to me. It isn't a reed relay - it's better. It's a MOSFET.

Of course, if you are sharing a ground plane, you could save thirty bucks and just...

Nah - go ahead, grandpa! Get that solid state relay!

 

[killivolt]

Looks good to me. It isn't a reed relay - it's better. It's a MOSFET.

Of course, if you are sharing a ground plane, you could save thirty bucks and just...

Nah - go ahead, grandpa! Get that solid state relay!

ha,ha oh well as ................ I need a reed relay and ok.

So, better off on recommendations then I guess.

duff, Thank you.

kv

Edit: This stuff keeps getting better.

 

[duffy]

Actually, I was going to suggest "just use a MOSFET". That's pretty much all that's in that solid-state DC relay, and you can drive them direct off a port pin when you are sharing a ground like that.

I don't see where you said what the load on this thing was - ? A reed isn't good for a huge amount of current. MOSFET's and that solid state relay are, though.

 

[killivolt]

Actually, I was going to suggest "just use a MOSFET". That's pretty much all that's in that solid-state DC relay, and you can drive them direct off a port pin when you are sharing a ground like that.

I don't see where you said what the load on this thing was - ? A reed isn't good for a huge amount of current. MOSFET's and that solid state relay are, though.

I have a bigger relay involved I am trying to close a contact point for a trigger of 30vdc to ground. It's the base of a transistor on a circuit with a 30 volt relay 55 watts which is what I read on the spec sheet when it's fully powered.

It can power contact points of 120vac for a light I want to drive.

I am also told that the status pin will be sturdy. Actually built for things like this I think driving it directly is a possibility but I would still like this one from Bancuk.

I plan to get all the parts list and circuit diagram drawn as things permit.

Can I Employ the Mosfet into this Diagram ?

kv

 

[killivolt]

If I replace the relay with another maybe the mosfet or solid state ?

kv

Edit: I corrected the circuit diagram and now it shows the hole circuit including the contacts and pull down Transistor BC557.

 

[killivolt]

If I replace the relay with another maybe the mosfet or solid state ?

kv