Re: Help with 12 volt rocket igniter

In article <nb4zj.7250$6R.6969@trnddc04>,
ehsjr <ehsjr@xxxxxxxxxxxxxxxx> wrote:

/
+---[igniter]---o o---+---[330R]---[LED]---+
| SW1 | |
| | |
| +------[Piezo]-------+
[Batt] 6V | |
| | / |
| +--------o o--------+
| SW2 |
| |
+-------------------------------------------+

Use a piezo that draws 10 mA or less, such as CAT# SBZ-365
from AllElectronics, and the total draw for the LED and
piezo will be under 20 mA. You can go to a 12 volt battery
if you want, and change the resistor to 1K.

A slightly different, perhaps better, version:
/
+------o o--+-----+---+---[580R]---[LED-G]-+----------+
| SW1 | | | | |
| | | | / | |
| [580R] | +--------o o--------+ |
[Batt] 6V | | SW2 |
| or | [Piezo] [ignitor]
| 12V | | |
| [LED-R] | |
| | | |
+------------+-----+-----------------------------------+

SW1 should be a keyed switch which can only have the key removed when
off. The key should always be in hand when approaching the rocket.

The LEDs will light, albeit not very brightly, with 6V. In my
experience, 12V is more reliable for launching, and easier to find. If
doing a dedicated 6V version, go back to the 330 or 280 ohms.

In this version, LED-R (red) and the annoying noise both indicate that
the arming switch (SW1) is on, and that there is power. If the annoying
noise is on, don't approach rocket - that's an improvement (IMHO) over
Ed's version in terms of safety, if using a noisemaker. The current from
those does not pass through the ignitor.

LED-G (green) indicates a good connection of the ignitor wires (though
it can't tell a short from an ignitor, so be careful when connecting
wires at the rocket.) SW2 is the launch pushbutton.

Regardless of what circuit you use, remember not to approach the rocket
for at least a minute in the event of a launch failure. Sometimes they
smolder and go off.

If you like, you can replicate the right side of the circuit (beyond the
piezo) to make a multiple-rocket launcher (where you'd set up 2 or more
launch rods and rockets, and launch either at the same time, or in quick
succession). In practice I've found that this is not usually very
useful, as it increases the likelihood of losing the rockets, trying to
track more than one at a time.

--
Cats, coffee, chocolate...vices to live by
.