Alt-BEAM Archive
Message #02554
To: Salem Smith flamable@inetnebr.com
From: Steven Bolt sbolt@xs4all.nl
Date: Thu, 22 Apr 1999 16:50:46 +0200 (CEST)
Subject: [alt-beam] Re: SE help again
On Thu, 22 Apr 1999, Salem Smith wrote:
> Hey its me again. I have taken Steve's advice and tried to debug my FLED SE
> but its still doing the same thing. I have a 2N3904 and a 2N3906 that I am
> using now, but I have also used 2N2222A and 2N2907 combinations. Everything
> gives the same reaction. The 4.5 VDC 100mA converter with a 2.2K resistor
> charges the 2200uF cap (I have connected some caps to get up to 5500uF).
> Then the FLED fades in and starts to flash then.... "twitch" .....the motor
> kinda convulses and the whole process starts over.
Judging by the size of your storage cap, I suspect that your SE is
working as specified. 2200uF is not enough for a storage cap, if
you use a small recorder motor. And even 5500uF will provide much
less than a second of running time. If you want to see it run for a
few seconds, try the smallest super cap (47000uF).
It's not that the recorder motor lacks efficiency. Inertia is the
problem here. The fairly large diameter and mass of the rotor
demands a kick with some oomph; at less than 4700uF, the voltage
will drop too fast when the SE fires, so the rotor doesn't get
going properly. Your best combination of transistors is probably a
2N3906 and a 2N2222, as the latter is able to switch more of the
high initial current to the motor.
Some time ago I put an fled SE together using a BC559C, a BC337 and
a red fled. It sort of worked, triggering at about 2.1V, even when
the supply current at trigger level was limited to about 70uA - much
less than reported by others. In any sort of light a slowly rising
voltage would lock up the fled; black tape solved that. A more
persistent problem was oscillation. It happened after every trigger
pulse, no matter what kind of motor was used. At low simulated light
levels the oscillation damped out, but if the `sun' was bright enough,
it would persist and prevent recharge. Separating the latch and
driver stages is imho the best way to avoid such oscillations.
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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