Re: receiver question 1b: interference [TANKS]

["Amir Tahvildaran" <adt22-at-drexel.edu>]

Uh-oh, educational content...

Thanks, I'll try to squeeze in as many more questions as I can before you go 
on vacation ;)

----- Original Message ----- 
From: "Frank Pittelli" <frank-at-rctankcombat.com>
To: <tanks-at-rctankcombat.com>
Sent: Wednesday, June 21, 2006 10:41 PM
Subject: Re: receiver question 1b: interference [TANKS]


> Amir Tahvildaran wrote:
>> I'm seeing some kind of interference from the trigger firing - I hooked 
>> up the second channel (1/2 channel) of the MRC to a door lock actuator 
>> (via a relay) and now when I fire and release it, the turret rotate jolts 
>> a little - the scorpion mini is somehow activated (it coincides with the 
>> relays clicking).  Right now I'm guessing I should have diodes somewhere 
>> in the mix, but again would appreciate any pointers.
>
> WARNING ---- Educational Content Follows ----  WARNING
>
> Whenever a coil is de-energized, the collapsing magnetic field generates a 
> voltage spike (sometimes quite high) that *travels in the opposite 
> direction* of the normal current flow that energized the coil.  Since 
> relays consist of a powerful coil, they generate a powerful spike.  The 
> voltage spike traveling down the wires in turn generates an RF signal that 
> can be picked up at quite a distance.
>
> In order to eliminate these effects, you need to hook a diode across the 
> coil wires *in the reverse direction*.  That is, you should connect the 
> diode so that it *does not* pass current when you want to activate the 
> coil.  Then, when the coil deactivates and spikes, the diode will allow 
> the reverse pulse to shunt to ground quickly, thereby limiting it's 
> effect.
>
> Basically, whenever you use a relay, you should use a diode on the control 
> lines.  Since the relay coil doesn't draw much current and the reverse 
> spike doesn't generate much current (although the voltage can be quite 
> high), a small capacity diode (e.g., 1 amp) should suffice.
>
> I use two LEDs on my trigger relay.  One that lights when the coil is 
> activated and the other that lights when it is deactivated.  It provides a 
> nice indication of what is happening.
>
> Frank P.
>
>
>
>