Model Rocket Launcher Help

[manumenzella]

Hi. I am building a model rocket launcher with countdown, safe key, etc.
The firing fuse that lights up the motor (just a low resistance wire that heats up the engine) is conected to a logic level mosfet, or NPN transistor. My question is: as soon as the PIC powers up, for a very short time, can it put the ports to HIGH and fire the rocket before I want to???
I need it to be very safe so kids and other people can play with it.
Thanks a lot, and sorry for my english.
Manuel

[viewgsm]

Hi,
Just to be sure , use a PULL DOWN resistor (10K is fine ) to the GND

Good luck with ur project , sounds fun

[manumenzella]

Hi. Thanks for your answer!!!!
Sorry to bother you again, my english is not very good! The resistor to ground will keep the transistor off even if for a tiny lenght of time the pic pin is held high, right?????? (NPN transistor or N channel MOSFET)
Thanks for making it clear!!!!!!!!!!
Manuel

[T_J_W]

I would place a turn key safty switch in line to make sure.

Tim

[BobK]

Hi Manuel,

You should check the nuts & volts website as a model rocket launcher was a PIC project I believe early in 2006.

I was looking into building a couple for my grandsons that was fully automatic with an ISD chip providing the countdown over a loud speaker adding the various system checks. I thought of using a relay to prevent accidental ignition. Have it wired normally open until a specific point in the countdown then if the other safety checks were okay then the relay would be switched on enabling launch voltage ready for the count to reach zero.

I was heavy into rocketry as a kid myself! Have fun.

BobK

[Acetronics2]

Hi, Manu

It's a VERY common Pic issue : defining pin states at power up ...

so, it's easy but relatively unknown ...

1) Write your output intial state : PORTx = % 00110010 i.e.

2) Select input or output : TRISx = % 11000001 i.e.

yes ... so simple as this !!!

Alain

[viewgsm]

Hi

I agree with Acetronics
also this PULL-DOWN will not help if the pin went high for low time ,
this will help to keep your PIN pulled to the ground (NOT FLOOATING) in case the pin was setuped as input or AN .

good luck

[BigWumpus]

After any reset the Pins will be set as input - for you, they will be tristate!
So, add the pull-down-resistor an write a good programm !

[manumenzella]

Hi there. Thanks a lot for all your answers!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Its great to be able to ask for help and get it so quick!!!!
I will use the pull-down resistor and be sure to configure the port to output low.
Thanks a lot again! Great forum!
Manuel