Of Mice and HV (fwd)

["High Voltage list" <hvlist@xxxxxxxxxx>]

Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Tue, 11 Apr 2006 07:20:03 +0930
From: Matthew Smith <matt@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Of Mice and HV

Greetings All

CONTENT WARNING: If you are distressed by nasty things happening to
vermin (small furry creatures to those not infested with them), please
do not read any further.

They don't make 'em like they used to!  Our house, completed just over
two years ago (actually not completed, but that's another story!)
appears to have been built to accommodate rodents just as comfortably as
humans.

Snap traps have proved anything but reliable (bait gone, trap still set)
and when they do operate, frequently kill in an unclean manner.

So, I have decided to build an electric mousetrap.  Idea is simple:
mouse enters trap and has to pass through a narrow gap between two
aluminium plates arranged in a V.  (Mouse enters the larger part of the
V.)  One plate is fixed, the other against light spring tension so that
the subject has to push between the two plates to get to the bait.

Plates are connected to a charged capacitor.  Charging will be from a
PWM supply driven by a microcontroller which stops when capacitor
voltage reaches an upper threshold and starts again once it has
discharged (mostly through the feedback voltage divider) down to a
minimum voltage.  The idea being that this device is battery-operated
and tries to save power.

Does anyone have any idea what minimum voltage I would need to apply to
guarantee fatal fibrillation?

I had considered powering from a disposable camera supply (no
microcontroller - simply pulse the start button when the neon goes out)
but, whilst photoflash capacitors can give us a ghastly bite, is the
300V or so enough to take out a mouse in its insulating fur coat?  I've
serviced equipment before where mice have gone in a mains (240V) PSU and
have blown the fuses but am still unsure about the certainty of a clean
kill.

Once I've got this idea working, I want to motorise it so that the
defunct rodent can be cleared from the plates and the trap be readied
for another "client".

Cheers

M

-- 
Matthew Smith
IT Consultancy & Web Application Development
http://www.kbc.net.au