5v Long Run
rapscaLLion
Posts: 75
Hey all,
Suppose I have a string of eight relays wired in parallel, connected by Cat 5 cable, spread out over 500 feet.
If I have a CMOS4050 sending a 5v signal down the line to activate the relays, will the signal make it to all the relays without too much line loss? They need 3.3v as a minimum to trigger.
Will this work? My calculations for 24AWG Cat5 says yes, but I don't have enough experience to be comfortable with my unverified calculations, and unfortunately I don't have 500' to test with.
If not, what would the simplest way to boost/repeat the signal be?
Looking for simplest possible solution here.
Many thanks!
Alex
Suppose I have a string of eight relays wired in parallel, connected by Cat 5 cable, spread out over 500 feet.
If I have a CMOS4050 sending a 5v signal down the line to activate the relays, will the signal make it to all the relays without too much line loss? They need 3.3v as a minimum to trigger.
Will this work? My calculations for 24AWG Cat5 says yes, but I don't have enough experience to be comfortable with my unverified calculations, and unfortunately I don't have 500' to test with.
If not, what would the simplest way to boost/repeat the signal be?
Looking for simplest possible solution here.
Many thanks!
Alex
Comments
e=i*r
5-3.3=i*30.2
i=0.056
so the math says as long as the relays total current is less then 56mA you are ok.
i think it unlikely you relays draw less then 7mA each. There are some ways to cheat this though. for example if the relays are only on for short pulses you can have a large cap beside each relay.
your best bet would be to use a higher line voltage or have a boost power supply at each one. using 24V would be a cheaper options requiring only a transister and second power supply.
24V would allow each relay to draw 86mA each.
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This might help a bit..
CMOS gates are not to great at putting out much power,
So you will need a driver of some kind.
MOSFETS are well suted to doing this kind of simple switching .. Just be sure to add a diode across the coil .
If it was me I would do this ( see attachment)
Cat5 has 8 wires you only need 3 this way ..
What Kind of Load are you switching ??
Peter
KG6LSE
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Post Edited (Peter KG6LSE) : 12/7/2009 12:53:16 AM GMT
So basically there are 8 units across the line, each with access to 24v off of which operate a small power supply for some LEDs. The relay switches them on an off rapidly as needed. The signal cable (Cat5) is independent of the power. However, since these units are existing it would be very difficult to add components into the box unless it is very simple. This is due to space and mostly time!
In terms of the CMOS chip, that is on a separate controller and would be easy to change. What if I just attached another relay to the controller and sent 12v or 24v down the line? Would that work better? I'm just trying to avoid having to modify the power supply boxes.
Would the MOSFETS still be a good idea?
Thanks a ton!
Alex
Post Edit -- X 8 = 14.4 mA.· You could do that from 1 Stamp pin.· The 500' thing is hinkey, but other than that -- eh.
Post Edited (PJ Allen) : 12/7/2009 1:10:39 AM GMT
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24 bit LCD Breakout Board now in. $21.99 has backlight driver and touch sensitive decoder.
Just out of curiosity, what would the practical and theoretical length limit be for the cat5?
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24 bit LCD Breakout Board now in. $21.99 has backlight driver and touch sensitive decoder.
also this is using only 1 pair. if you use all 4 pairs you can quadruple the length
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24 bit LCD Breakout Board now in. $21.99 has backlight driver and touch sensitive decoder.
Thanks a ton, that's really helpful. I can actually use all four pairs, would I tie them all to the CMOS4050, or would I put them each on a different output (with the same signal being sent)?
As it stands we don't have a 1000' cable run anyhow, in fact I think the max will be 600 or less.
It's difficult to work within constraints because I know there are probably more "ideal" ways to do this, but thanks for helping me make this work.
Alex
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24 bit LCD Breakout Board now in. $21.99 has backlight driver and touch sensitive decoder.