Photocell Bonus
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Re: Photocell Bonus
can someone tell me how to set up a photocell? I tried setting them up with a motor, but nothing's happening. Do need batteries or something?
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Re: Photocell Bonus
p-----------------X----Battery----X------------|rocketchicka wrote:can someone tell me how to set up a photocell? I tried setting them up with a motor, but nothing's happening. Do need batteries or something?
p-----------------X------------------------------|Motor
p= photocell
X= joint
-= wire?
|= motor
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Re: Photocell Bonus
Use the setup on the first page under the Wiki. It works perfectly on some motors. Some motors have way too much current and too little resistance to work with a photocell. We tried several motors until we found a couple that worked well under the amount of photoresistors we put in and the light source. None of them worked at full power because there was always some resistance still left in the photocells even under some very bright lights.
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Re: Photocell Bonus
I updated both the fist post in this thread and the wiki diagrams to be more clear about what design should be used (remove all references to that random resistor), reworded some stuff that has been made irrelevant because of the rules clarifications, and hopefully made it more obvious that a battery was required in the circuit.
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Re: Photocell Bonus
I was able to get the motor in this solar racer kit to spin with just the light from a common 2-cell mini-maglite.
[Click Photos to Enlarge]
These kits are pretty expensive (in my opinion), but it gives you some idea of the size of the motor. You could replace the photo-voltaic photocells with photo resistors connected in parallel and a battery as explained above. These tiny motors are often available from surplus liquidators. I have bought them from Radio Shack. They were being sold as replacement motors for the small re-chargeable radio-controlled cars.
Kits from Tamiya, such as the "Blue Eagle" and "Honda Dream", have motors that are about the same length and are about twice the diameter.
[Click Photo to Enlarge]
As a much less expensive source you might try googleing for somthing like "surplus pager motor"
[Click Photos to Enlarge]
These kits are pretty expensive (in my opinion), but it gives you some idea of the size of the motor. You could replace the photo-voltaic photocells with photo resistors connected in parallel and a battery as explained above. These tiny motors are often available from surplus liquidators. I have bought them from Radio Shack. They were being sold as replacement motors for the small re-chargeable radio-controlled cars.
Kits from Tamiya, such as the "Blue Eagle" and "Honda Dream", have motors that are about the same length and are about twice the diameter.
[Click Photo to Enlarge]
As a much less expensive source you might try googleing for somthing like "surplus pager motor"
Information expressed here is solely the opinion of the author. Any similarity to that of the management or any official instrument is purely coincidental! Doing Science Olympiad since 1987!
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Re: Photocell Bonus
Proving that solar cells could have worked. I don't know why they banned them - there is so little choice in this year's rules already.fleet130 wrote:I was able to get the motor in this solar racer kit to spin with just the light from a common 2-cell mini-maglite.
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Re: Photocell Bonus
I had two devices have working photocells at this past weekend's invitational. One was from my team, done the night before with one working test beforehand.
ELECTRONICS GOLDMINE sells a pack of tiny 3v cellphone vibrating motors for (I think) $2.50. We also got a dozen of the 75 cent photocells on sale. While we were at it, we got an assortment of gearhead motors; real powerful and nice and slow.
Photocells had a bright resistance of 24 ohms. This was low enough to be a problem! So, each photocell was wired in series with a 24 ohm resistor to bring the bright resistance UP to 50 ohms. This effectively increased the number of photocells needed to four, but it eliminated overheated photocells, which causes aggravating intermittent problems.
Hooked up to 9v (D cells-- we don't use those rectangular niners), there was plenty of voltage and power available to run the 3v cell pager motor, which hopped around on a precarious spot, fell about 50cm, reached the end of its wire, and tripped a really touchy snap switch.
ELECTRONICS GOLDMINE sells a pack of tiny 3v cellphone vibrating motors for (I think) $2.50. We also got a dozen of the 75 cent photocells on sale. While we were at it, we got an assortment of gearhead motors; real powerful and nice and slow.
Photocells had a bright resistance of 24 ohms. This was low enough to be a problem! So, each photocell was wired in series with a 24 ohm resistor to bring the bright resistance UP to 50 ohms. This effectively increased the number of photocells needed to four, but it eliminated overheated photocells, which causes aggravating intermittent problems.
Hooked up to 9v (D cells-- we don't use those rectangular niners), there was plenty of voltage and power available to run the 3v cell pager motor, which hopped around on a precarious spot, fell about 50cm, reached the end of its wire, and tripped a really touchy snap switch.
Uncle Fester, Maker & Fiction Science Writer
The Misadventures of the Electric Detention
The Revenge of the Electric Detention
The Curse of the Electric Detention
>> Three full-length adventures, 26 short stories and counting!
The Misadventures of the Electric Detention
The Revenge of the Electric Detention
The Curse of the Electric Detention
>> Three full-length adventures, 26 short stories and counting!
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Re: Photocell Bonus
Aha, that might explain some of the things we have been experiencing - the CDS cells seem inconsistent, which has been driving us nuts. I'll try the resistor.Uncle Fester wrote: Photocells had a bright resistance of 24 ohms. This was low enough to be a problem! So, each photocell was wired in series with a 24 ohm resistor to bring the bright resistance UP to 50 ohms. This effectively increased the number of photocells needed to four, but it eliminated overheated photocells, which causes aggravating intermittent problems.
BTW, what kind of light source are you using?
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Re: Photocell Bonus
One combo that seems to be working nicely-
9.6v battery from a portable drill. 12v lamp Home depot- landscaping light, oh, 1/14" diameter; seriously bright w/ 9.6v battery; photoresistor about 1/4" in front of the lamp in a little box. Photoresistor to a Radio Shack 5v relay, relay to a 12v computer cooling fan. Fan reaction time to when the light is tripped is almost instantaneous, and plenty wind from the fan to push a paddle on the top of a lever (pivoted at the bottom); lever falls.....leads to the next action....
9.6v battery from a portable drill. 12v lamp Home depot- landscaping light, oh, 1/14" diameter; seriously bright w/ 9.6v battery; photoresistor about 1/4" in front of the lamp in a little box. Photoresistor to a Radio Shack 5v relay, relay to a 12v computer cooling fan. Fan reaction time to when the light is tripped is almost instantaneous, and plenty wind from the fan to push a paddle on the top of a lever (pivoted at the bottom); lever falls.....leads to the next action....
Len Joeris
Fort Collins, CO
Fort Collins, CO
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Re: Photocell Bonus
Problem with the arrangement immediately above, the fan motor gets none of its electricity from/through the photocell(s). It gets it through a switch contact (relay).
Answer to the latest question addressed to me: the photocells were lit up by a $1.00 dollar-store 3-LED tap light, and the whole setup was enclosed in a bright shiny coffee can, with the lid sprayed with black spray-on "plasti-dip" that's used on tools and such for waterproofing. Kids chose that because itw as black and thick.
Answer to the latest question addressed to me: the photocells were lit up by a $1.00 dollar-store 3-LED tap light, and the whole setup was enclosed in a bright shiny coffee can, with the lid sprayed with black spray-on "plasti-dip" that's used on tools and such for waterproofing. Kids chose that because itw as black and thick.
Uncle Fester, Maker & Fiction Science Writer
The Misadventures of the Electric Detention
The Revenge of the Electric Detention
The Curse of the Electric Detention
>> Three full-length adventures, 26 short stories and counting!
The Misadventures of the Electric Detention
The Revenge of the Electric Detention
The Curse of the Electric Detention
>> Three full-length adventures, 26 short stories and counting!
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