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[OT]Wire length recommendations

 
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Kamal



Joined: 11 Feb 2006
Posts: 12

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[OT]Wire length recommendations
PostPosted: Sun Jan 07, 2007 1:58 pm     Reply with quote
Hi

I am using a PIC as a control unit to switch a few HBridges on and off according to an schedule algorithm.

The initiation of the schedule is triggered by pressing of 4 switches on a switch board which I have to keep atleast 4 meters from the control unit.

Will just extending 4 meter wires from the PIC pins (with a 10k pullup or pulldown) to the switch board work ?

I am worried about the long length of the wires playing havoc with the PIC Control unit.

Please advise.
newguy



Joined: 24 Jun 2004
Posts: 1911

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PostPosted: Sun Jan 07, 2007 2:16 pm     Reply with quote
If all you're using those 4 wires for is to ground the pic's inputs, it should be fine @ 4m. The only thing you have to worry about is those 4m wires picking up EMI (they're big antennae). With an appropriate RC low pass filter you should be fine. If the environment is particularly noisy, you may also have to install ferrite beads and some sort of diode clamping arrangement or zeners to ensure that the voltage at the pic's inputs doesn't exceed Vdd.
kender



Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley

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shielding against EMI
PostPosted: Sun Jan 07, 2007 3:24 pm     Reply with quote
newguy wrote:
The only thing you have to worry about is those 4m wires picking up EMI (they're big antennae). With an appropriate RC low pass filter you should be fine. If the environment is particularly noisy, you may also have to install ferrite beads and some sort of diode clamping arrangement or zeners to ensure that the voltage at the pic's inputs doesn't exceed Vdd.

I would also mention shieldng as a way of combatting EMI. Usually, the shield would be grounded to the chassis on one end only. If your have high frequency EMI, you would also ground the other end through a capacitor.
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