Help with MOSFET as switch.

Feb 18, 2005 3 Replies
M

Hi all



I'm looking to control some devices from my computer. I've decided to play around with the parallel port.



I've gotten this advice from somebody.



================================================================== Output multiplexer for parallel port:

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Initial condition, C0 and C1 high



1 put address of 373 on data bus (0 to 15)
2 toggle C1
3 put 373 data on bus
4 toggle C0 Three of these could be driven from one port by using C2 and C3 instead of C0 To drive your loads use (logic level mosfet)s (google) You will get hits like:
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==================================================================

I've very intersted in doing this, as I'm looking to control 100+ devices. For starters I'm just looking to switch some LED's on and off after the 373's. I'm not sure what mosfets to use and how exactly to tie them into the diagram mentioned above. In the end I'm wanting to switch 1 amp.



Eventually I'm going to also want to add in a continuity check (LED that operates on less than 50 milli amps) on each of the connections to the switching device after the 373. I'm probably going to be placing some sort of terminal block in there for easy connection.



Any advice is appreciated.


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D
2n7000 type do a google search

Also ST's VPN series logic level power mosfets

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Hi all

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R

If you want to control power and not just turn on a few LEDs, you *must* use an opto-isolated or relay isolated interface to your parallel port. Otherwise, sooner or later, your experiments will blow up the parallel port - and because so much is integrated within a single chip, this can take out the whole motherboard. You might want to just build the isolation bit in a nice sealed box, and then add your mosfets etc in a separate unit.

Roger

To get the isolation and minimise the risk you might want to buy a kit. Other

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F

1) Have a Look-see if someone has done it for you:

The "1-Wire Bus (tm)", "I2C" or the "CAN" protocol might have some cool devices associated with them, that *might* do "whatever" for you.

2) Always say *What* you want to achieve because that makes the question easier to answer:

If you want to switch some channels that are close together *and* want continuity check, but do not care much for speed, there are relay/lamp driver chips that can be clocked serially with a string of bits and then latched to "engage" the command. Maxim would be a good place to start.

If you want speed, maybe someone has done it for you in USB or CAN.

If you need to be clever and each switch is separated by some distance etc. then some control modules with protocols and all might be what you need. CAN, RS-485, ZigBee...

In any case, you need isolation because once you blow up the printer port, the motherboard is dead - all the peripherals sit in one chip!

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