Re: Circuit Design Help

On Sat, 20 Jan 2007 02:57:26 -0500, buyem <buyem@xxxxxxxxxxx> wrote:

I haven't designed a circuit in more years then I care to mention so I
know I need help.
What I want to do is .. control a table saw and a shop vac.
When I turn the circuit ON...table saw and shop/vac on immediately
When I turn the circuit OFF... table saw off immediately and shop/vac to
run for approx. 5 seconds longer and then turn off.
If your able and/or willing to help I'll give you the specs for both
pieces of equipment.

Save yourself some trouble and buy a ready made "delay on off" time
delay relay?

Plan B would be a solid state relay with a large (~1,000 uf- 5,000ur)
cap holding up the "coil" voltage for 5 seconds. But that would
require a simple basic low voltage power supply to energize the relay.

Plan C use a low voltage control relay, power supply, and mosfet
transistor to switch the relay off when a cap on the gate discharges
below its threshold value (cap can be ~10 uf). Cap charges through a
diode and turns on relay immediately turning on the dust collector.
Cap discharges through a suitably large resistor across it after power
is removed (1-4.7 megohm). Downside is the LV supply has to stay on
24/7. The LV supply could be off and dust collector started manually
with a push button, or switched with the power to the saw if that's
convenient/desirable.
'-- '

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