Suitable relay driver

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Edwaaaad
Posts: 5
Joined: Fri Mar 17, 2006 9:15 am
Location: Wellington, New Zealand

Suitable relay driver

Post by Edwaaaad »

Hey Everyone,

I need my Io warrior 40 to drive a series of very small relays (coil 5v d.c)
I was wondering if anyone had a suitable driving circuit that they had already tried and proven? This could save me a lot of trouble.
I want to be able to drive 10 - 16 of these relays per io warrior in the long term so I assume I am going to need to externally power them? In saying that each relay only draws something in the range of 40mA, but if i have more than one Io looped off a usb port I assume the p.c will only give me 500mA collectively, not per IO?
Guido Körber
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Post by Guido Körber »

You can use discrete transistors, you can have a look at the 74xxx TTL chip family, there are octal driver chips that should work, you can use ULN2803, but then you should put inverters in front of them to make sure the relays close on low output since the default state of the IO-Warrior pins is high.

What do you mean with "more than one Io looped off a usb port"?
Edwaaaad
Posts: 5
Joined: Fri Mar 17, 2006 9:15 am
Location: Wellington, New Zealand

Post by Edwaaaad »

Sorry, more than 1 IO Warrior looped off the usb, can you do this?
I assume you dont need a seperate usb port for each IOW used? Can I set up several IOW's as a compound device using a hub of some description? If so, with the highest current draw allowed being 500mA, in this situation is this per usb port, or per device?
Robert Marquardt
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Post by Robert Marquardt »

One device per port. USB is a bus so simply splitting the lines electrically is doomed from the start.
It is 100 mA or 500 mA to the device = IO-Warrior. So if you properly connect several IO-Warriors each one can get 500 mA.
If the device gets 500 mA or only 100 mA is negotiated with the hub via bus protocol. If the hub is self poweed then it can hand out 500 mA per port whereas if the hub is bus powered then it can only hand out 100 mA per port.
Edwaaaad
Posts: 5
Joined: Fri Mar 17, 2006 9:15 am
Location: Wellington, New Zealand

Post by Edwaaaad »

Thanks People, Good to know.
Regards
Edwaaaad
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