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Hi Mike,
The 74HC14 is more effcient for this application than a 74AC14. This single Schmitt inverter cmos oscillator has an input voltage that always hovers near the input switching thresholds and as such is not as efficient as a two inverter oscillator with a large input swing. Also the dark "SE" uses simple diode connected between the slowly changing solar cell output voltage and the cmos input. As the cmos input voltage is near the trigger level the Vcc starts to increase and can quickly drain the storage capacitor.
Also keep in mind that a blue led requires about 3V to turn on. Since the LED pump at most doubles the voltage across the LED, the blue LED quickly fades out when the voltage on the cap (Vcc) drops to about 1.8V (check).
I tested this circuit with a red LED which needs about 1.6V and therefore the LED pump circuit can continue to operate until Vcc drops to about 0.9V.
There is a tripler version of this circuit which is more suitable for a blue LED.
Let us know what's on your wishlist and we can try to custom design something.
wilf
----- Original Message -----From: Mike ScharfSent: Friday, February 25, 2005 2:00 PMSubject: [beam] Pummer AC or HC Question about Wilf Circuit
Hi group!
I was tinkering around with one of wilf's pummer designs last night
and I have a question. First of all, the circuit I'm referring to is
now located in the files section as "LEDPUMP.png". Now, I think I
already know the answer, but, would this circuit be much different
depending on whether I used a HC or an AC type chip?
The circuit worked VERY nicely with a miniature blue led, however
even with a 1F cap (charged to 2 volts) it didn't look like it was
going to blink for very long. After like 20-30 minutes, the brightness
was obviously suffering. Wilf stated in his associated post that it
was blinking well even after 8 hours when he made it. I had to use a
74AC14 cause the only HC ones I have are SMD parts. I can use these
SMD pieces but, I can't breadboard with them. So I just wonder if the
performance would be greatly improved before I go and make a nice
brass frame and do all this building for a pummer.
BTW, I am REALLY excited about this pummer! It will be my first one!
Thanks All!
Mike Scharf :)
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